Precise measurements of light from distant quasars suggest the value of the fine-structure constant may have changed over the history of the universe. If confirmed, this would have enormous significance for the foundations of physics. Measurements of light from quasars billions of years in the past can be used to determine the value of fundamental constants like the fine-structure constant at early times and test if they have remained constant.
The document discusses particle physics and the mysteries it aims to investigate, such as the nature of the universe immediately after the Big Bang and physics at extremely high temperatures not seen since shortly after the universe formed. It also summarizes efforts to detect the hypothesized Higgs boson and explore ideas like supersymmetry and the possibility of extra dimensions to help explain mysteries like why gravity is so much weaker than other forces. The document advocates continued investigation into these deep questions to advance understanding of fundamental aspects of nature.
The document summarizes a study that uses strong and weak gravitational lensing to analyze the mass distribution of 28 galaxy clusters. Key findings include:
- The concentration parameter cvir is found to steeply decrease with increasing mass, approximately following cvir ∝ Mvir-0.59±0.12, consistent with theoretical predictions for high-mass clusters but observationally inferred concentrations are higher for lower-mass clusters possibly due to baryon cooling effects.
- Stacking weak lensing shear profiles also supports a steep mass-concentration relation.
- Stacking weak lensing shear maps with position angle information from strong lensing indicates significant ellipticity of the mean mass distribution, with a best-fit ellipticity
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
This document discusses a proposed explanation for dark energy and the accelerated expansion of the universe involving antimatter hidden in cosmic voids. It suggests that general relativity extended to antimatter predicts a gravitational repulsion between matter and antimatter. Observational evidence of faster than expected void evacuation and structure formation in our local region could be explained by the antigravity field produced by antimatter masses equivalent to typical superclusters hidden in voids. This "dark repulsor" model could account for dark energy and various anomalies without needing an initial explosion or a cosmological constant.
A multiband study_of_hercules_a_ii_multifrequency_vlaSérgio Sacani
This document summarizes a multi-frequency study of the radio galaxy Hercules A using the VLA radio telescope. The observations revealed that the bright jets and prominent rings have a flatter spectrum than the surrounding lobes and bridge, suggesting they represent a recent outburst from the active nucleus. The magnetic field closely follows the edges of the lobes, jets, and rings. There is also an asymmetry in the spectral properties between the two lobes that can be explained by relativistic beaming and light travel delays.
1) Barnard 68 is considered a stable dense molecular cloud core, but observations indicate it should be gravitationally unstable and collapsing.
2) The authors argue Barnard 68 is experiencing a collision with another small core that will trigger its gravitational collapse within the next 200,000 years, forming a low-mass star.
3) Such core mergers may play an important role in triggering star formation and shaping properties of molecular cores and the stellar initial mass function.
Detection of visible light from the darkest worldSérgio Sacani
This document reports the detection of visible light from the exoplanet TrES-2b using Kepler photometry data. The analysis finds a day-night contrast amplitude of 6.5 ± 1.9 parts per million, representing the lowest amplitude orbital phase variation discovered. This signal is detected at a confidence level of 99.98% and persists across different models of the data, appearing robust. If interpreted as scattering, it corresponds to a geometric albedo of 0.0253±0.0072 for TrES-2b, making it the darkest exoplanet detected so far. However, models indicate significant day-side emission, implying an even lower true albedo.
This document summarizes observations of the debris disk around the subgiant star κ CrB using Herschel and Keck. Herschel spatially resolved images of the debris disk, the first such images of a disk around a subgiant star. Keck radial velocity monitoring provided evidence for a second planetary companion around κ CrB. Keck adaptive optics imaging placed an upper limit on the mass of this companion. Modeling of the Herschel images showed the dust is broadly distributed but could not distinguish between a single wide belt or two narrow belts. The observations are consistent with dynamical depletion or collisional erosion clearing the inner regions of the disk.
The document discusses particle physics and the mysteries it aims to investigate, such as the nature of the universe immediately after the Big Bang and physics at extremely high temperatures not seen since shortly after the universe formed. It also summarizes efforts to detect the hypothesized Higgs boson and explore ideas like supersymmetry and the possibility of extra dimensions to help explain mysteries like why gravity is so much weaker than other forces. The document advocates continued investigation into these deep questions to advance understanding of fundamental aspects of nature.
The document summarizes a study that uses strong and weak gravitational lensing to analyze the mass distribution of 28 galaxy clusters. Key findings include:
- The concentration parameter cvir is found to steeply decrease with increasing mass, approximately following cvir ∝ Mvir-0.59±0.12, consistent with theoretical predictions for high-mass clusters but observationally inferred concentrations are higher for lower-mass clusters possibly due to baryon cooling effects.
- Stacking weak lensing shear profiles also supports a steep mass-concentration relation.
- Stacking weak lensing shear maps with position angle information from strong lensing indicates significant ellipticity of the mean mass distribution, with a best-fit ellipticity
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
This document discusses a proposed explanation for dark energy and the accelerated expansion of the universe involving antimatter hidden in cosmic voids. It suggests that general relativity extended to antimatter predicts a gravitational repulsion between matter and antimatter. Observational evidence of faster than expected void evacuation and structure formation in our local region could be explained by the antigravity field produced by antimatter masses equivalent to typical superclusters hidden in voids. This "dark repulsor" model could account for dark energy and various anomalies without needing an initial explosion or a cosmological constant.
A multiband study_of_hercules_a_ii_multifrequency_vlaSérgio Sacani
This document summarizes a multi-frequency study of the radio galaxy Hercules A using the VLA radio telescope. The observations revealed that the bright jets and prominent rings have a flatter spectrum than the surrounding lobes and bridge, suggesting they represent a recent outburst from the active nucleus. The magnetic field closely follows the edges of the lobes, jets, and rings. There is also an asymmetry in the spectral properties between the two lobes that can be explained by relativistic beaming and light travel delays.
1) Barnard 68 is considered a stable dense molecular cloud core, but observations indicate it should be gravitationally unstable and collapsing.
2) The authors argue Barnard 68 is experiencing a collision with another small core that will trigger its gravitational collapse within the next 200,000 years, forming a low-mass star.
3) Such core mergers may play an important role in triggering star formation and shaping properties of molecular cores and the stellar initial mass function.
Detection of visible light from the darkest worldSérgio Sacani
This document reports the detection of visible light from the exoplanet TrES-2b using Kepler photometry data. The analysis finds a day-night contrast amplitude of 6.5 ± 1.9 parts per million, representing the lowest amplitude orbital phase variation discovered. This signal is detected at a confidence level of 99.98% and persists across different models of the data, appearing robust. If interpreted as scattering, it corresponds to a geometric albedo of 0.0253±0.0072 for TrES-2b, making it the darkest exoplanet detected so far. However, models indicate significant day-side emission, implying an even lower true albedo.
This document summarizes observations of the debris disk around the subgiant star κ CrB using Herschel and Keck. Herschel spatially resolved images of the debris disk, the first such images of a disk around a subgiant star. Keck radial velocity monitoring provided evidence for a second planetary companion around κ CrB. Keck adaptive optics imaging placed an upper limit on the mass of this companion. Modeling of the Herschel images showed the dust is broadly distributed but could not distinguish between a single wide belt or two narrow belts. The observations are consistent with dynamical depletion or collisional erosion clearing the inner regions of the disk.
1) The gamma-ray burst GRB 101225A is explained as being caused by the tidal disruption of a minor body (such as an asteroid or comet) falling onto an isolated neutron star.
2) The light curves and spectra observed across multiple wavelengths are consistent with the predictions of the tidal disruption model.
3) A minor body passing within 105-106 km of a neutron star would be disrupted by the star's tidal forces, with the debris falling back to form an accretion disk around the star and emitting radiation.
Three newly discovered_globular_clusters_in_ngc6822Sérgio Sacani
This document describes the discovery of three new globular clusters in the Local Group dwarf irregular galaxy NGC 6822. The authors present optical photometry of the clusters from archival CFHT/Megacam data. Two clusters are luminous and compact, while the third is a lower luminosity diffuse cluster. The positions of the new clusters are consistent with the linear alignment of previously known clusters in NGC 6822. Studying globular cluster systems in dwarf galaxies provides insights into the formation of larger galaxies through accretion and mergers.
Apartes de la Conferencia de la SJG del 14 y 21 de Enero de 2012: Neutrino ma...SOCIEDAD JULIO GARAVITO
This document discusses a novel method for determining neutrino mass spectra using gravitational waves and neutrinos from supernovae. It proposes that two bursts of gravitational waves could be generated during neutrino oscillations in supernovae: one from neutrinos converting from left-handed to right-handed states via interaction with the magnetic field of the expanding plasma, and another when some of these right-handed neutrinos flip back to left-handed flavors later due to a different interaction. Measuring the time delay between the arrival of neutrinos and gravitational waves could directly measure neutrino masses, since massive neutrinos would be delayed relative to massless gravitational waves. This could provide a new way to determine absolute neutrino masses that does not depend on mass-squared differences
A possible carbonrich_interior_in_superearth_55_cancrieSérgio Sacani
1) The document analyzes the possibility that the interior of the super-Earth exoplanet 55 Cancri e could be carbon-rich rather than oxygen-rich.
2) Models that assume an oxygen-rich interior with iron, silicates, and a water envelope cannot fully explain 55 Cancri e's mass and radius measurements. However, a carbon-rich interior containing iron, silicon carbide, and/or carbon could explain the observations without needing a volatile envelope.
3) A carbon-rich interior for 55 Cancri e is plausible given the reported carbon-rich composition of its host star, though more data is needed on the star's elemental abundances and the planet's atmosphere.
This document presents aluminum abundances for about 100 red giant stars in each of the Galactic globular clusters 47 Tuc and M 4. The abundances were derived from intermediate-resolution FLAMES/GIRAFFE spectra, focusing on the Al I doublet at 8772-8773 Å. Previous homogeneous abundances of O, Na, Mg, and Si were also analyzed to study multiple stellar populations in these clusters. The data confirm two stellar populations are visible in M 4, while 47 Tuc shows evidence of at least three distinct stellar groups based on the abundances of O, Na, Mg, Al, and N.
Non xrays from_the_very_nearby_typeia_sn_2014j_constraints_on_its_environmentSérgio Sacani
Deep X-ray observations of SN 2014J reveal no X-ray emission down to a luminosity limit of Lx < 7 × 1036 ergs−1, constraining the mass-loss rate of the progenitor system to be < 10−9 M☉/yr. Alternatively, the SN shock could be expanding into a uniform medium with density < 3 cm−3. These results rule out single-degenerate systems with steady mass transfer until explosion and constrain unstable hydrogen burning systems to have recurrence times < 300 years. Allowed progenitors include double white dwarf systems or systems where mass transfer ceased before explosion.
X ray emission-from_strongly_asymmetric_circumstellar_material_in_the_remnant...Sérgio Sacani
This document summarizes a study of X-ray emission from circumstellar material (CSM) in the remnant of Kepler's supernova. The researchers used a statistical technique to isolate X-ray emission from CSM versus ejecta based on spectral characteristics. They found that most CSM is distributed along the bright north rim, but substantial amounts are also projected against the center, indicating a disk-like distribution of CSM from the progenitor system before the supernova. Hydrodynamic simulations support an AGB star companion as the origin of the asymmetric CSM. Quantitative analysis of magnesium emission identifies CSM and requires Kepler to have originated from a close binary system.
The significance of_the_integrated_sachs_wolfe_effect_revisitedSérgio Sacani
The document discusses revisiting measurements of the integrated Sachs-Wolfe (ISW) effect in light of new data. It updates the data set used in a previous study to include the latest cosmic microwave background and large-scale structure data. Testing finds the updated results are consistent with previous measurements, with the combined ISW detection significance being 4.4 sigma. The paper also addresses criticisms raised about potential systematic errors, focusing on a rotation test of maps, but finds no evidence of additional contamination.
The document presents observations of the starburst galaxy NGC 253 using near-infrared imaging and spectroscopy as well as mid-infrared spectroscopy. The observations are used to derive physical properties of the starburst such as the star formation rate, stellar population, and evolutionary stage. Evolutionary synthesis modeling is applied to interpret the observations and show that the starburst in NGC 253 is in a late phase, has been ongoing for 20-30 million years, and is consistent with a modified Salpeter initial mass function.
This document summarizes a study analyzing far-infrared spectra of Saturn's rings obtained by the Cassini spacecraft. The authors modeled the spectra to estimate the size distribution of regolith grains on ring particles. They found that the spectra were best fit by a broad size distribution ranging from 1 micron to 1-10 cm, with a power law index of around 3. This suggests that the largest regolith grains are comparable in size to the smallest visible ring particles. The abundance of smaller grains was found to increase with decreasing solar phase angle, likely due to cooling effects in Saturn's shadow.
Modulations in the_radio_light_curve_of_the_typeiib_supernova_2001igSérgio Sacani
This document summarizes radio observations of the Type IIb supernova SN 2001ig made with the Australia Telescope Compact Array and Very Large Array over 700 days. The observations found periodic deviations from the standard model of radio light curves that are consistent with recurring density modulations in the circumstellar medium with a period of around 150 days. This provides evidence that the progenitor was a Wolf-Rayet star in a binary system with an eccentric 100 day orbit, causing regular build-up of circumstellar material. Such binary systems are thought to produce Type Ib/c supernovae through envelope stripping, linking these events to Type IIb supernovae.
This document summarizes a study that uses cosmological simulations to model the formation of stellar halos around galaxies via the tidal disruption of accreted dwarf galaxies. The simulations follow the dynamical evolution and disruption of satellites from high redshift in a fully cosmological setting. The simulations produce stellar halos with masses and density profiles consistent with observations of the Milky Way and M31. The stellar halos show complex structures composed of well-mixed components, tidal streams, shells, and other substructures rather than smooth distributions.
Plutino an accidental_quasi-satellite_of_plutoSérgio Sacani
Plutino 15810 (1994 JR1) is currently in a 1:1 mean motion resonance with Pluto, following a quasi-satellite path where its mean longitude circulates with a superimposed libration. N-body simulations show it will remain in this quasi-satellite state, where it moves around Pluto like a retrograde satellite but with a non-closed trajectory, for nearly 350,000 years. This makes 15810 the first known minor body in a 1:1 resonance with Pluto and the first quasi-satellite discovered in the trans-Neptunian region. The quasi-satellite behavior is triggered by the object's 2:3 mean motion resonance with Neptune.
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
The document discusses astrophysics concepts related to stars, including:
1. The main energy source of stars is hydrogen fusion, which occurs through either the proton-proton chain or CNO cycle depending on the star's core temperature.
2. A star's luminosity, temperature, radius, mass, chemical composition, and age can be used to characterize it. Its luminosity can be calculated using the Stefan-Boltzmann law.
3. A star's spectrum provides information about its surface temperature, chemical composition, and whether it is part of a binary system.
Fox m quantum_optics_an_introduction_photon antibunching1Gabriel O'Brien
This chapter discusses photon antibunching and the Hanbury Brown-Twiss experiments which helped develop modern quantum optics. It introduces the second-order correlation function g(2)(τ) which can be used to classify light as antibunched, coherent, or bunched. The chapter then discusses how the Hanbury Brown-Twiss experiments measured intensity fluctuations in light beams and how this led to defining g(2)(τ). It explores how g(2)(τ) can take different values for classical versus quantum light, with antibunched light only possible due to quantum effects.
FINAL 2014 Summer QuarkNet Research – LHCb PaperTheodore Baker
The document summarizes the author's 2014 summer research analyzing decay data from the LHCb detector. The author analyzed several decay channels including Λ c → Ξ− K+ π+, Ω b
−
→ Ω− J/ψ, and D s
+ → K− K+ π+. For the Λ c decay, the author found evidence of a Ξ0 resonance. For the Ω b decay, the author measured the mass but found the lifetime fit was off. For the D s decay, the author observed decays through φ(1020) and K*(892) resonances. The author was unable to find evidence of the hypothesized Ω cb
0 baryon due
Evidence for a black hole remnant in the type iil supernova 1979 cSérgio Sacani
1) The Type IIL supernova SN 1979C has exhibited a remarkably constant X-ray luminosity of (6.5 ± 0.1) × 1038 erg s−1 over 12 years of observations from 1995 to 2007.
2) This steady luminosity is inconsistent with models of a supernova powered by a magnetar or expanding into a dense circumstellar wind, as the luminosity would be expected to decrease over time in these models.
3) The authors propose that the steady X-ray emission provides evidence for accretion onto a stellar-mass (5-10 solar mass) black hole remnant at the center of SN 1979C. Spectral modeling of the X-ray data is consistent with emission from
A LUMINOUS Be+WHITE DWARF SUPERSOFT SOURCE IN THE WING OF THE SMC: MAXI J0158...Carlos Bella
This document summarizes a study of the X-ray source MAXI J0158-744, which was detected by the MAXI instrument in November 2011. It exhibited an unusually bright and brief X-ray flare with a luminosity exceeding 10^39 erg/s, approaching ultraluminous X-ray source levels. Follow-up observations with Swift and other instruments over subsequent months found the source had a very soft X-ray spectrum characteristic of a supersoft source. Optical spectra of the counterpart revealed emission and absorption features consistent with a B1/2IIIe spectral type star in the Small Magellanic Cloud. The authors propose MAXI J0158-744 is a luminous supersoft source associated with
EMU M.Sc. Thesis Presentation
Thesis Title: "Dark Matter; Modification of f(R) or WIMPS Miracle"
Student: Ali Övgün
Supervisor: Prof. Dr. Mustafa Halilsoy
This document summarizes an article that proposes an alternative explanation for dark energy and dark matter based on a modified theory of gravity. It begins by providing background on dark matter and dark energy in standard cosmology and the evidence that supports their existence. It then outlines the proposed alternative theory, which modifies Einstein's field equations by adding a function of the Ricci scalar. This introduces new curvature terms that could potentially drive accelerated expansion, providing an alternative to dark energy. The theory aims to match observations without requiring dark matter or energy, but reduces to general relativity in the solar system scale where it has been tightly tested.
1) The gamma-ray burst GRB 101225A is explained as being caused by the tidal disruption of a minor body (such as an asteroid or comet) falling onto an isolated neutron star.
2) The light curves and spectra observed across multiple wavelengths are consistent with the predictions of the tidal disruption model.
3) A minor body passing within 105-106 km of a neutron star would be disrupted by the star's tidal forces, with the debris falling back to form an accretion disk around the star and emitting radiation.
Three newly discovered_globular_clusters_in_ngc6822Sérgio Sacani
This document describes the discovery of three new globular clusters in the Local Group dwarf irregular galaxy NGC 6822. The authors present optical photometry of the clusters from archival CFHT/Megacam data. Two clusters are luminous and compact, while the third is a lower luminosity diffuse cluster. The positions of the new clusters are consistent with the linear alignment of previously known clusters in NGC 6822. Studying globular cluster systems in dwarf galaxies provides insights into the formation of larger galaxies through accretion and mergers.
Apartes de la Conferencia de la SJG del 14 y 21 de Enero de 2012: Neutrino ma...SOCIEDAD JULIO GARAVITO
This document discusses a novel method for determining neutrino mass spectra using gravitational waves and neutrinos from supernovae. It proposes that two bursts of gravitational waves could be generated during neutrino oscillations in supernovae: one from neutrinos converting from left-handed to right-handed states via interaction with the magnetic field of the expanding plasma, and another when some of these right-handed neutrinos flip back to left-handed flavors later due to a different interaction. Measuring the time delay between the arrival of neutrinos and gravitational waves could directly measure neutrino masses, since massive neutrinos would be delayed relative to massless gravitational waves. This could provide a new way to determine absolute neutrino masses that does not depend on mass-squared differences
A possible carbonrich_interior_in_superearth_55_cancrieSérgio Sacani
1) The document analyzes the possibility that the interior of the super-Earth exoplanet 55 Cancri e could be carbon-rich rather than oxygen-rich.
2) Models that assume an oxygen-rich interior with iron, silicates, and a water envelope cannot fully explain 55 Cancri e's mass and radius measurements. However, a carbon-rich interior containing iron, silicon carbide, and/or carbon could explain the observations without needing a volatile envelope.
3) A carbon-rich interior for 55 Cancri e is plausible given the reported carbon-rich composition of its host star, though more data is needed on the star's elemental abundances and the planet's atmosphere.
This document presents aluminum abundances for about 100 red giant stars in each of the Galactic globular clusters 47 Tuc and M 4. The abundances were derived from intermediate-resolution FLAMES/GIRAFFE spectra, focusing on the Al I doublet at 8772-8773 Å. Previous homogeneous abundances of O, Na, Mg, and Si were also analyzed to study multiple stellar populations in these clusters. The data confirm two stellar populations are visible in M 4, while 47 Tuc shows evidence of at least three distinct stellar groups based on the abundances of O, Na, Mg, Al, and N.
Non xrays from_the_very_nearby_typeia_sn_2014j_constraints_on_its_environmentSérgio Sacani
Deep X-ray observations of SN 2014J reveal no X-ray emission down to a luminosity limit of Lx < 7 × 1036 ergs−1, constraining the mass-loss rate of the progenitor system to be < 10−9 M☉/yr. Alternatively, the SN shock could be expanding into a uniform medium with density < 3 cm−3. These results rule out single-degenerate systems with steady mass transfer until explosion and constrain unstable hydrogen burning systems to have recurrence times < 300 years. Allowed progenitors include double white dwarf systems or systems where mass transfer ceased before explosion.
X ray emission-from_strongly_asymmetric_circumstellar_material_in_the_remnant...Sérgio Sacani
This document summarizes a study of X-ray emission from circumstellar material (CSM) in the remnant of Kepler's supernova. The researchers used a statistical technique to isolate X-ray emission from CSM versus ejecta based on spectral characteristics. They found that most CSM is distributed along the bright north rim, but substantial amounts are also projected against the center, indicating a disk-like distribution of CSM from the progenitor system before the supernova. Hydrodynamic simulations support an AGB star companion as the origin of the asymmetric CSM. Quantitative analysis of magnesium emission identifies CSM and requires Kepler to have originated from a close binary system.
The significance of_the_integrated_sachs_wolfe_effect_revisitedSérgio Sacani
The document discusses revisiting measurements of the integrated Sachs-Wolfe (ISW) effect in light of new data. It updates the data set used in a previous study to include the latest cosmic microwave background and large-scale structure data. Testing finds the updated results are consistent with previous measurements, with the combined ISW detection significance being 4.4 sigma. The paper also addresses criticisms raised about potential systematic errors, focusing on a rotation test of maps, but finds no evidence of additional contamination.
The document presents observations of the starburst galaxy NGC 253 using near-infrared imaging and spectroscopy as well as mid-infrared spectroscopy. The observations are used to derive physical properties of the starburst such as the star formation rate, stellar population, and evolutionary stage. Evolutionary synthesis modeling is applied to interpret the observations and show that the starburst in NGC 253 is in a late phase, has been ongoing for 20-30 million years, and is consistent with a modified Salpeter initial mass function.
This document summarizes a study analyzing far-infrared spectra of Saturn's rings obtained by the Cassini spacecraft. The authors modeled the spectra to estimate the size distribution of regolith grains on ring particles. They found that the spectra were best fit by a broad size distribution ranging from 1 micron to 1-10 cm, with a power law index of around 3. This suggests that the largest regolith grains are comparable in size to the smallest visible ring particles. The abundance of smaller grains was found to increase with decreasing solar phase angle, likely due to cooling effects in Saturn's shadow.
Modulations in the_radio_light_curve_of_the_typeiib_supernova_2001igSérgio Sacani
This document summarizes radio observations of the Type IIb supernova SN 2001ig made with the Australia Telescope Compact Array and Very Large Array over 700 days. The observations found periodic deviations from the standard model of radio light curves that are consistent with recurring density modulations in the circumstellar medium with a period of around 150 days. This provides evidence that the progenitor was a Wolf-Rayet star in a binary system with an eccentric 100 day orbit, causing regular build-up of circumstellar material. Such binary systems are thought to produce Type Ib/c supernovae through envelope stripping, linking these events to Type IIb supernovae.
This document summarizes a study that uses cosmological simulations to model the formation of stellar halos around galaxies via the tidal disruption of accreted dwarf galaxies. The simulations follow the dynamical evolution and disruption of satellites from high redshift in a fully cosmological setting. The simulations produce stellar halos with masses and density profiles consistent with observations of the Milky Way and M31. The stellar halos show complex structures composed of well-mixed components, tidal streams, shells, and other substructures rather than smooth distributions.
Plutino an accidental_quasi-satellite_of_plutoSérgio Sacani
Plutino 15810 (1994 JR1) is currently in a 1:1 mean motion resonance with Pluto, following a quasi-satellite path where its mean longitude circulates with a superimposed libration. N-body simulations show it will remain in this quasi-satellite state, where it moves around Pluto like a retrograde satellite but with a non-closed trajectory, for nearly 350,000 years. This makes 15810 the first known minor body in a 1:1 resonance with Pluto and the first quasi-satellite discovered in the trans-Neptunian region. The quasi-satellite behavior is triggered by the object's 2:3 mean motion resonance with Neptune.
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
The document discusses astrophysics concepts related to stars, including:
1. The main energy source of stars is hydrogen fusion, which occurs through either the proton-proton chain or CNO cycle depending on the star's core temperature.
2. A star's luminosity, temperature, radius, mass, chemical composition, and age can be used to characterize it. Its luminosity can be calculated using the Stefan-Boltzmann law.
3. A star's spectrum provides information about its surface temperature, chemical composition, and whether it is part of a binary system.
Fox m quantum_optics_an_introduction_photon antibunching1Gabriel O'Brien
This chapter discusses photon antibunching and the Hanbury Brown-Twiss experiments which helped develop modern quantum optics. It introduces the second-order correlation function g(2)(τ) which can be used to classify light as antibunched, coherent, or bunched. The chapter then discusses how the Hanbury Brown-Twiss experiments measured intensity fluctuations in light beams and how this led to defining g(2)(τ). It explores how g(2)(τ) can take different values for classical versus quantum light, with antibunched light only possible due to quantum effects.
FINAL 2014 Summer QuarkNet Research – LHCb PaperTheodore Baker
The document summarizes the author's 2014 summer research analyzing decay data from the LHCb detector. The author analyzed several decay channels including Λ c → Ξ− K+ π+, Ω b
−
→ Ω− J/ψ, and D s
+ → K− K+ π+. For the Λ c decay, the author found evidence of a Ξ0 resonance. For the Ω b decay, the author measured the mass but found the lifetime fit was off. For the D s decay, the author observed decays through φ(1020) and K*(892) resonances. The author was unable to find evidence of the hypothesized Ω cb
0 baryon due
Evidence for a black hole remnant in the type iil supernova 1979 cSérgio Sacani
1) The Type IIL supernova SN 1979C has exhibited a remarkably constant X-ray luminosity of (6.5 ± 0.1) × 1038 erg s−1 over 12 years of observations from 1995 to 2007.
2) This steady luminosity is inconsistent with models of a supernova powered by a magnetar or expanding into a dense circumstellar wind, as the luminosity would be expected to decrease over time in these models.
3) The authors propose that the steady X-ray emission provides evidence for accretion onto a stellar-mass (5-10 solar mass) black hole remnant at the center of SN 1979C. Spectral modeling of the X-ray data is consistent with emission from
A LUMINOUS Be+WHITE DWARF SUPERSOFT SOURCE IN THE WING OF THE SMC: MAXI J0158...Carlos Bella
This document summarizes a study of the X-ray source MAXI J0158-744, which was detected by the MAXI instrument in November 2011. It exhibited an unusually bright and brief X-ray flare with a luminosity exceeding 10^39 erg/s, approaching ultraluminous X-ray source levels. Follow-up observations with Swift and other instruments over subsequent months found the source had a very soft X-ray spectrum characteristic of a supersoft source. Optical spectra of the counterpart revealed emission and absorption features consistent with a B1/2IIIe spectral type star in the Small Magellanic Cloud. The authors propose MAXI J0158-744 is a luminous supersoft source associated with
EMU M.Sc. Thesis Presentation
Thesis Title: "Dark Matter; Modification of f(R) or WIMPS Miracle"
Student: Ali Övgün
Supervisor: Prof. Dr. Mustafa Halilsoy
This document summarizes an article that proposes an alternative explanation for dark energy and dark matter based on a modified theory of gravity. It begins by providing background on dark matter and dark energy in standard cosmology and the evidence that supports their existence. It then outlines the proposed alternative theory, which modifies Einstein's field equations by adding a function of the Ricci scalar. This introduces new curvature terms that could potentially drive accelerated expansion, providing an alternative to dark energy. The theory aims to match observations without requiring dark matter or energy, but reduces to general relativity in the solar system scale where it has been tightly tested.
This document summarizes a study that uses distance measurements in the nearby universe to test theories of modified gravity. The study compares distance measurements from cepheid variable stars, tip of the red giant branch stars, and water masers in different galaxies. These distance indicators operate in gravitational fields of different strengths, enabling tests of scalar-tensor gravity theories where fifth forces are screened to different extents depending on the local gravitational potential. The study finds no evidence for the enhanced gravitational forces predicted by chameleon and symmetron screening scenarios, constraining the parameter space of these theories.
Direct detection of ultralight dark matter bound to the Sun with space quantu...Sérgio Sacani
Recent advances in quantum sensors, including atomic clocks, enable searches for a broad range of dark matter candidates. The question of the dark matter distribution in the Solar system critically affects the reach of dark matter direct detection experiments. Partly motivated by the NASA Deep Space Atomic Clock and the Parker Solar Probe, we show that space quantum sensors present new opportunities for ultralight dark matter searches, especially for dark matter states bound to the Sun. We show that space quantum sensors can probe unexplored parameter space of ultralight dark matter, covering theoretical relaxion targets motivated by naturalness and Higgs mixing. If a two-clock system were able to make measurements on the interior of the solar system, it could probe this highly sensitive region directly and set very strong constraints on the existence of such a bound-state halo in our solar system. We present sensitivity projections for space-based probes of ultralight dark matter, which couples to electron, photon and gluon fields, based on current and future atomic, molecular and nuclear clocks
The document discusses dark matter and provides evidence for its existence from various astronomical observations. It notes that while ordinary matter makes up only about 4% of the universe, dark matter accounts for about 23%. Various properties of dark matter are described, including that it interacts gravitationally but does not emit or absorb light. Possible candidates for dark matter are discussed, including WIMPs (Weakly Interacting Massive Particles), which are favored from both astronomical data and particle physics models. The document outlines how WIMPs could have been thermally produced in the early universe to account for the observed dark matter abundance.
The document discusses the debate around defining what constitutes a galaxy versus a star cluster. It focuses on "ultra compact dwarf" (UCD) objects and ultra-faint dwarf spheroidal galaxies, which have properties intermediate between traditional galaxies and globular clusters. The document considers possible criteria to distinguish galaxies from clusters, such as minimum size, relaxation time, presence of dark matter or satellite systems. It aims to promote discussion on developing an accepted definition of a galaxy and invites readers to vote on their preferred definition.
A structure in_the_early_universe_at_z_1_3_that_exceeds_the_homogeneity_scale...Sérgio Sacani
This document summarizes the discovery of an exceptionally large quasar group (LQG) in the Sloan Digital Sky Survey (SDSS) DR7 quasar catalog, designated U1.27. The LQG, termed the "Huge-LQG", contains 73 quasars within a redshift range of 1.1742 to 1.3713, and has a characteristic size of approximately 500 megaparsecs (Mpc), making it the largest LQG found to date. Its size suggests incompatibility with the expected homogeneity scale in the standard cosmological model and challenges the cosmological principle.
This document introduces an alternative theoretical framework to Einstein's theory of special relativity called Realitivistic Relativity 2.0. It proposes that star systems and atomic systems are fundamentally similar, with stars behaving like protons and planets like electrons. The author derived mathematical relationships between celestial objects and their quantum counterparts with high accuracy. This work maps objects in star systems to particles in atoms and vice versa, challenging existing interpretations of physics. It aims to simplify and unite physics through reexamining data from first principles without preconceived theories.
This document introduces an alternative theoretical framework to Einstein's theory of special relativity. It proposes that star systems and atomic systems are equivalent, with stars behaving as celestial atoms moving at different velocities. Celestial objects like planets are proposed to mathematically map to their quantum counterparts. The hypothesis suggests gas giant planets may represent celestial electrons, rock planets the atomic nucleus, and stars protons. The work aims to develop a simplified unified model of physics through reexamining relationships between phenomena.
Overview of GTR and Introduction to CosmologyPratik Tarafdar
This document provides an overview of general relativity and an introduction to cosmology. It discusses key concepts such as:
- General relativity builds on Einstein's theory that gravity curves spacetime.
- The principle of equivalence states that inertial and gravitational mass are equivalent.
- Einstein's field equations relate the curvature of spacetime to the energy and momentum within it.
- Tests of general relativity include observations of orbiting bodies like Mercury, gravitational lensing, and the detection of gravitational waves.
- The cosmological principle states that the universe is homogeneous and isotropic on large scales.
The objective of this paper is to propose an approach to the unification of physics by attempting
to construct a physical worldview which can be used as the context for a unified physical theory.
The underlying principle is that we have to construct a clear description of the physical world
before we can build a unified physical theory.
The present state of physics is such that there are many theories which all differ in the descriptive
context in which they operate. The theories of general relativity, quantum theory, quantum
electrodynamics, string theory and the standard model of particle physics are based on differing
concepts of the nature of the physical world.
The document discusses the speed of light and why it appears as a constant in monotheism books. It explains that the speed of light is the same for all forces including light and electromagnetic waves like ultraviolet, infrared, radio, and TV. It is the upper limit speed in the universe and cannot be reached by matter due to the infinite energy needed. It then describes how analyzing the moon's motion in an isolated earth-moon system can be used to define the speed of light based on the moon's perfectly circular orbit and other orbital parameters in this system. Making these calculations precisely, the author determines that the speed of light defined from the isolated earth-moon system equations is 299,792.458 km/s, which matches
String theory proposes that fundamental particles are not point-like but are tiny vibrating strings. It aims to unify quantum mechanics and general relativity by incorporating gravity into a theory of everything at very small scales. String theory predicts that spacetime has 10 dimensions rather than the observed 4 dimensions, with the extra 6 dimensions being curled up too small to detect directly. While strings have never been observed, string theory remains a promising area of research as the only known way to reconcile quantum mechanics and general relativity.
The document discusses the development of quantum mechanics and wave-particle duality, including de Broglie's hypothesis that all matter has an associated wave nature. It covers key concepts like the wave function, wave packets, Heisenberg's uncertainty principle, and the Schrödinger equation governing the motion of quantum particles. Experimental evidence for matter waves is also discussed, showing that even large molecules can exhibit wave-like behavior.
Relativity is a magnificent equality principle of nature at creating the universe.
However, it has many counter-intuitive, mind-blogging concepts, and many of us may have a hard time at understanding it.
How could light propagate in vacuum without a media?
How could the speed of light remain constant for all observers?
Why there are time dilation, length contraction, and loss of simultaneity?
Why the laws of nature remain the same for all moving frames?
How could space and time be bent by mass and energy?
Are our brains wired in such a way so that it is always difficult to understand relativity in a natural way?
Or there may exist a new knowledge framework, and a new representation so that relativity become easier to be understood.
This video offers a mechanical approach for the first time to explain relativity.
It attempts to make relativity easier for the general public to understand.
This document discusses the nature of gravity and its relationship to other forces and fields. It provides evidence that gravity is an emergent phenomenon that arises from an underlying non-gravitational theory. Specifically:
1) Gravity behaves differently than other forces in that it curves spacetime itself rather than being mediated by particle exchanges. However, quantum gravity theories propose gravitons as force-carrying particles.
2) Holographic duality theories from the 1990s demonstrated that gravitational theories in higher dimensions are equivalent to non-gravitational theories in lower dimensions.
3) Modern developments like string theory and the AdS/CFT correspondence provide concrete examples of holography and establish gravity as an emer
Gravitational Wave Astronomy is a fascinating discovery made a few years ago that changed the notions of modern physics. This presentation won the 3rd Prize in the SPIE student chapter's Oral Presetation in my college.
This document discusses physics and metaphysics, specifically laws governing gravity. It summarizes Newton's laws of motion and universal law of gravitation. It also summarizes Einstein's theories of special and general relativity. The document notes some limitations and fallacies in Newton's theory, and suggests gravity may be the result of an equilibrium between positive and negative forces maintaining a constant ratio. It proposes revising our understanding of gravitational laws from first principles.
A high-mass X-ray binary descended from an ultra-stripped supernovaSérgio Sacani
Ultra-stripped supernovae are diferent from other terminal explosions of massive
stars, as they show little or no ejecta from the actual supernova event1,2
. They are
thought to occur in massive binary systems after the exploding star has lost its surface
through interactions with its companion2
. Such supernovae produce little to no kick,
leading to the formation of a neutron star without loss of the binary companion,
which itself may also evolve into another neutron star2
. Here we show that a recently
discovered high-mass X-ray binary, CPD −29 2176 (CD −29 5159; SGR 0755-2933)3–6
, has
an evolutionary history that shows the neutron star component formed during an
ultra-stripped supernova. The binary has orbital elements that are similar both in
period and in eccentricity to 1 of 14 Be X-ray binaries that have known orbital periods
and eccentricities7
. The identifcation of the progenitors systems for ultra-stripped
supernovae is necessary as their evolution pathways lead to the formation of binary
neutron star systems. Binary neutron stars, such as the system that produced the
kilonova GW170817 that was observed with both electromagnetic and gravitational
energy8
, are known to produce a large quantity of heavy elements
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...Sérgio Sacani
Magmatic iron-meteorite parent bodies are the earliest planetesimals in the Solar System,and they preserve information about conditions and planet-forming processes in thesolar nebula. In this study, we include comprehensive elemental compositions andfractional-crystallization modeling for iron meteorites from the cores of five differenti-ated asteroids from the inner Solar System. Together with previous results of metalliccores from the outer Solar System, we conclude that asteroidal cores from the outerSolar System have smaller sizes, elevated siderophile-element abundances, and simplercrystallization processes than those from the inner Solar System. These differences arerelated to the formation locations of the parent asteroids because the solar protoplane-tary disk varied in redox conditions, elemental distributions, and dynamics at differentheliocentric distances. Using highly siderophile-element data from iron meteorites, wereconstruct the distribution of calcium-aluminum-rich inclusions (CAIs) across theprotoplanetary disk within the first million years of Solar-System history. CAIs, the firstsolids to condense in the Solar System, formed close to the Sun. They were, however,concentrated within the outer disk and depleted within the inner disk. Future modelsof the structure and evolution of the protoplanetary disk should account for this dis-tribution pattern of CAIs.
Signatures of wave erosion in Titan’s coastsSérgio Sacani
The shorelines of Titan’s hydrocarbon seas trace flooded erosional landforms such as river valleys; however, it isunclear whether coastal erosion has subsequently altered these shorelines. Spacecraft observations and theo-retical models suggest that wind may cause waves to form on Titan’s seas, potentially driving coastal erosion,but the observational evidence of waves is indirect, and the processes affecting shoreline evolution on Titanremain unknown. No widely accepted framework exists for using shoreline morphology to quantitatively dis-cern coastal erosion mechanisms, even on Earth, where the dominant mechanisms are known. We combinelandscape evolution models with measurements of shoreline shape on Earth to characterize how differentcoastal erosion mechanisms affect shoreline morphology. Applying this framework to Titan, we find that theshorelines of Titan’s seas are most consistent with flooded landscapes that subsequently have been eroded bywaves, rather than a uniform erosional process or no coastal erosion, particularly if wave growth saturates atfetch lengths of tens of kilometers.
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Climate extremes likely to drive land mammal extinction during next supercont...
Pwapr03webb
1. Precise measurements on the light from distant quasars suggest that the value
of the fine-structure constant may have changed over the history of the universe.
If confirmed, the results will be of enormous significance for the foundations of physics
Are the laws of nature
changing with time?
John Webb
WHAT do we mean by “the laws of na- What is the fine-structure constant?
NASA
ture”? The phrase evokes a set of divine Have the laws of nature remained the
and unchanging rules that transcend the same since the Big Bang some 13.5 bil-
“here and now” to apply everywhere lion years ago? Paul Dirac first posed
and at all times in the universe. The re- this question in 1937, and he was still
ality is not so grand. When we refer to interested in this idea when he visited
the laws of nature, what we are really the University of New South Wales
talking about is a particular set of ideas (UNSW) in Sydney in 1975 – where I
that are striking in their simplicity, that am now based. Dirac attempted to link
appear to be universal and have been the strength of gravity, which describes
verified by experiment. It is thus human the large-scale properties of the uni-
beings who declare that a scientific verse, with the various constants and
thory is a law of nature – and human numbers that characterize the small-
beings are quite often wrong. scale properties of the universe. In
The development of a scientific the- doing so, he claimed that one of the
ory has always followed the need to constants of nature, the strength of
understand an observation for which Are the fundamental constants changing? gravity, should change with time.
no satisfactory explanation previously Observations of light from distant quasars suggest Although observations subsequently
existed. When developing new theories, that they might be. ruled out Dirac’s ideas, advances in
physicists tend to assume that funda- many areas of physics and astronomy
mental quantities such as the strength of gravity, the speed have resulted in a whole new set of opportunities for us to
of light in a vacuum or the charge on the electron are all search for any hint that the constants of nature might vary.
constant. And when these theories are found to predict the The particular question that I have been vigorously pursuing
results of new observations, our belief that these quantities with colleagues at UNSW and elsewhere can be stated as
are actually fundamental constants becomes even stronger. follows: is the fine-structure constant really constant, or has
Moreover, despite the rapid changes in technology in re- its value changed over the history of the universe?
cent decades, the timescale on which fundamental new dis- The fine-structure constant, α, is a measure of the strength
coveries in physics are made is typically comparable to a of the electromagnetic interaction, and it quantifies the
human lifespan. This means that theories developed decades strength with which electrons bind within atoms and mole-
ago can appear as if they have been carved in granite. cules. It is defined as α ≡ e 2/hc ≈ 1/137, where e is the charge
The end result is a natural reluctance to change our under- on the electron, h is Planck’s constant divided by 2π, and c is
standing of the world. But it is vital to remember the limita- the speed of light in a vacuum. The fine-structure constant is
tions that have been involved in testing these assumptions. of particular interest because it is a dimensionless number.
Many of the experiments we carry out to test theories are This makes it even more fundamental than other constants
restricted to the here and now – to Earth-bound research labs such as the strength of gravity, the speed of light or the charge
or to the small part of the universe that we can observe with on the electron (see box on page 34).
telescopes. If we could somehow do our experiments in a dif- There are theoretical reasons why α and other dimension-
ferent place or at a different time, we might well find that the less constants might vary with time. The holy grail of theoret-
results are different. Indeed, that is what appears to happen ical physics is to find a single unified theory that describes the
when we measure something called the fine-structure con- four fundamental forces: gravity, electromagnetism, and the
stant in the very distant past. strong and weak nuclear forces. Although the strengths of
PHYSICS WORLD APRIL 2003 physicsweb.org 33
2. 1 Simulated quasar absorption spectrum Constants with and without dimensions
Nature presents us with various constants. Some of these
galaxy
quasar
constants, such as the fine-structure constant, are dimensionless
to Earth and are not expressed in terms of units. However, other constants,
such as the velocity of light or the mass of the proton, are
hydrogen absorption emission lines from the quasar dimensional and their numerical values depend entirely on the units
due to galaxy heavy-element absorption in which they are expressed. The laws of nature do not, of course,
signal (arbitrary units)
due to galaxy
depend on a man-made system of units.
To put this another way, if we want to measure a dimensional
constant, we need a “yardstick” to make the measurement. But if we
obtained one value when we measured the speed of light on a
Monday, say, and a different value when we measured it on a Friday,
how would we know that our yardstick had not shrunk or expanded?
We would not. Moreover, if we were to interpret our observations as
3500 4000 4500 5000 5500 6000 a change in the length of the yardstick, how could we verify it without
observed wavelength (Å) reference to a second yardstick? Again, we could not. And so on.
Quasars are highly luminous objects that emit light over a wide range of However, dimensionless constants are fundamental absolute
wavelengths (red line), with peaks at several wavelengths due to emission by
elements such as hydrogen, nitrogen, silicon, carbon and iron in the gas
numbers, measured without reference to anything else. Therefore, if
around the quasar. When light from the quasar passes near a galaxy on its we want to investigate if the laws of nature are changing we must
way to Earth, the gas around the galaxy causes a distinct pattern of measure dimensionless quantities such as the fine-structure
absorption lines in the quasar spectrum (green line). By measuring the constant or the ratio of the electron and proton masses.
wavelengths of the absorption lines due to heavy elements (on the right of
the figure) we can determine both the redshift of the gas and the value of the
fine-structure constant, α, at the time when the light from the quasar was
absorbed. Such observations suggest that the value of α was slightly smaller There are several ways to measure possible changes in α
billions of years ago. The plethora of absorption features at the shorter
wavelengths on the left are due to hydrogen at different redshifts.
with time. We can measure the absorption spectra of quasars
at different redshifts, as we have done at UNSW. We can com-
pare the “ticking rates” of atomic clocks made of different
these four forces differ, as do the distances over which they elements (see box on page 36). We can also study the cosmic
operate, most physicists believe that a unified theory will be microwave background or the creation of the elements in the
discovered. If such a theory is not found, a great deal of the early universe. However, one of the first methods used to
elegance and beauty of fundamental physics will be lost. probe how α might have changed over the past two billion
Einstein’s theory of gravity – the general theory of relativity years relies on what must be one of the most unusual proces-
– only requires three spatial dimensions. However, the lead- ses ever studied by physicists – the so-called natural nuclear
ing contender for a unified theory requires extra dimensions reactor at Oklo in Central Africa.
beyond our familiar three. We do not know if these unified
theories are correct, but if extra dimensions do exist, they The strange story of the Oklo reactor
must be tiny compared with our ordinary spatial dimensions. Natural uranium contains two isotopes. Uranium-235, the
The concept of attributing a “size” to a dimension may isotope that is useful for nuclear energy, is relatively rare and
seem strange but it is important. The current size of the uni- accounts for just 0.7% of all natural uranium. Its less-radioact-
verse is determined by the distance that light has travelled ive sibling, uranium-238, makes up the other 99.3%. In 1972
since the Big Bang (i.e. about 13.5 billion light-years) and by scientists from the French atomic energy commission noticed
the amount by which it has expanded since then. This means something mysterious in soil samples taken from a uranium
that the actual size of the universe is about 40 billion light- mine in Gabon in Central Africa: the relative abundance of
years and rising. uranium-235 was a factor of two lower than expected.
Are the extra dimensions predicted by unified theories also One possibility was that a band of hi-tech terrorists had
expanding at the same rate as the universe? The answer to been stealing and stockpiling the missing uranium for pur-
this question is no. If the tiny extra dimensions were expand- poses even more evil than blowing up innocent atolls. How-
ing at this rate, then the strength of gravity would also be ever, isotopes of various other elements also appeared to be
changing very rapidly, and there is no evidence for this. How- depleted in a pattern that was strikingly similar to that ob-
ever, it may be possible to infer the presence of these extra served among the waste products from modern nuclear re-
dimensions – if they exist – by detecting small changes in the actors. The most plausible explanation is that there must once
strength of gravity or the other three forces. have been a “natural” nuclear reactor at Oklo. Although nat-
It has been predicted, for instance, that “large” extra dimen- ural nuclear reactors were predicted by Paul Kuroda of the
sions might cause small deviations in the inverse-square law University of Arkansas as long ago as 1956, Oklo is the only
of gravity over distances of less than 1 mm. However, recent known example (see photograph opposite).
measurements by John Price and co-workers at the Univer- What appears to have happened is that oxygenated water
sity of Colorado at Boulder have failed to find any evidence slowly dissolved the uranium-235 that was stored in surface
for this over distances of about 100 µm ( J C Long et al. 2003 rock about two billion years ago. Back then the natural con-
Nature 421 922). This is just one of many experiments that centration of uranium-235 would have been about 3% – it
have been set up to perform high-precision tests on constants, is much lower now because uranium-235 decays about six
forces and fundamental symmetries in recent years. times faster than uranium-238. Over time the uranium-235
34 physicsweb.org PHYSICS WORLD APRIL 2003
3. ANDREAS MITTLER
Natural wonder – measurements obtained at the natural nuclear reactor at Oklo in Central Africa can place limits on any possible change in the value of the
fine-structure constant over the past two billion years.
would have become concentrated in nearby algae mats, as it was just over eight minutes ago because that is how long
which acted as filters, and eventually enough of it would have it takes the light from the Sun to reach the Earth. Similarly,
collected to reach criticality and form a natural nuclear re- some quasars are so far away that we see them as they were
actor. This reactor would have “burned” the uranium-235, billions of years ago. Indeed, by observing quasars we can
thus explaining the low levels of the isotope found at Oklo. build up a continuous “universal history” that starts when the
But what has this got to do with α? In 1976, four years after universe was only about one billion years old and continues
the Oklo reactor was discovered, Alexander Shlyakhter of up to the present day.
the Leningrad Nuclear Physics Institute made the connec- However, we cannot study α with any reasonable precision
tion. Samples from Oklo revealed a relative abundance of using the quasars themselves. Rather, we must examine what
samarium-149 that was a factor of 45 lower than other ter- happens when the radiation from a quasar passes through a
restrial samples and Shlyakhter showed that ambient neut- galaxy that lies between the Earth and the quasar. The quasar
rons could convert samarium-149 into samarium-150 if they emits light over a broad range of wavelengths (figure 1). How-
had exactly the right energy. ever, when this light passes through the gas around the galaxy,
This resonance was due to a delicate balance between the a characteristic pattern of absorption lines will be super-
strong nuclear force and the repulsive electromagnetic force imposed on it.
in samarium. Moreover, the resonance energy depended on The presence of an absorption line at a particular wave-
α, so if the value of α was different two billion years ago, then length reveals that a specific element is present in the gas
the depletion of samarium-149 would also have been differ- cloud, and the width of each line shows the quantity of the
ent. The details of the calculation are complicated, but they element that is present. In addition to hydrogen, which is
show that any fractional change in the value of α since the ubiquitous in the universe, these “bar codes” reveal that the
time that Oklo was active cannot be greater than 10–7 (see gas clouds contain a range of other elements, including mag-
Olive et al. in further reading). nesium, iron, zinc, silicon, aluminium and chromium.
Very recently a new geological measurement technique Moreover, the bar code reveals what was happening when
known as “rhenium dating” has produced potentially even the light passed through the cloud, which could have hap-
more stringent results. The ages of iron meteorites obtained pened as long ago as just one billion years after the Big Bang.
using rhenium dating are consistent with those found by Although the gas cloud would have evolved into something
other methods. From this we can show that the beta-decay quite different by today, its bar code provides us with a perma-
lifetime of rhenium cannot have changed by more than 0.5% nent imprint of its state in the distant past – including infor-
over the age of the solar system. This translates to an upper mation about the value of α at that time.
limit on any fractional change in the value of α of the order Therefore, if we compare the bar codes that we find in
10–7 over about 4.6 billion years. quasar absorption spectra with the bar codes we measure for
While 4.6 billion years is a long time, the universe itself is the same atoms and ions in the laboratory, we can find out if
about 13.5 billion years old. Is it possible to test for changes the physics that is responsible for the absorption of radiation
in the value of α even earlier in the history of the universe? by atoms has changed over the history of the universe. In
The answer is yes – with the help of quasars. other words, we can find out if α has changed.
Using quasars to look at the fine-structure constant Back to the laboratory
Quasars are compact but highly luminous objects. Indeed, Back in 1998 I began collaborating with my colleagues Victor
they are so luminous that they can be studied in intricate Flambaum and Vladimir Dzuba at UNSW and John Bar-
detail using ground-based telescopes despite being vast dis- row, now at Cambridge University in the UK. Although both
tances away from us. We think that quasars contain black Victor and I worked in the same department, neither of us
holes at their centres and that the immense gravitational force had been aware of a common interest until he discovered that
exerted by the black hole is extremely efficient at converting I was looking for a student to help me in my efforts to use
matter in its vicinity into light. quasars to explore whether α had been different in the past.
Nature kindly co-operates by scattering quasars throughout The advantage of pooling his theoretical expertise with my
the universe. Since quasars are seen in all directions in the sky, experimental work quickly became apparent as we realized
they provide a powerful way of charting almost the entire that we could improve the precision of the measurements of
universe. And, like any astronomical object, whenever we α by an order of magnitude by analysing existing astrophy-
look at a quasar we see it as it was in the past. We see the Sun sical data in a new way.
PHYSICS WORLD APRIL 2003 physicsweb.org 35
4. Searching for changes in the fine-structure constant using atomic clocks
John Harrison would not have believed the corresponding increase in the precision of the clock.
precision of the latest atomic clocks. Despite his But what has this got to do with the fine-structure
mechanical genius, a clock made out of atoms – constant, α? It is not surprising to find that the
rather than cogs and springs – would surely resonance frequency relies on α. Moreover, if α is
surprise him. The H4 clock with which Harrison changing with time, clocks made from different
eventually won the £20 000 prize offered by the elements will “tick” at slightly different rates.
Board of Longitude in 1714 for a solution to the Therefore, by comparing the stability of two clocks
problem of finding longitude at sea was accurate to made of different elements it should be possible to
39 seconds over 47 days, or 1 part in 105. place an upper limit on any variation of α with time.
However, the latest atomic clocks are accurate to Unlike the quasar and Oklo results, experiments
one second in 50 million years, or 1 part in 1015. with atomic clocks probe the stability of α as it is
This level of accuracy makes it possible to search today rather than billions of years ago.
for any variations in the fine-structure constant A recent experiment by Harold Marion and co-
over timescales of years. workers at the Observatoire de Paris and the Ecole
The world’s most precise atomic clocks are now Normale Supérieure (ENS) compared the rates of
made from “atomic fountains”. A gas of atoms cesium and rubidium fountain clocks over a five-
within a vacuum chamber is trapped by a set of year period. If α is changing, the rate of change,
intersecting laser beams and cooled to a 1/α (dα/dt), must be less than –0.4 ± 16 × 10–16
temperature close to absolute zero. The ball of per year (see further reading). This is not in conflict
atoms is then tossed vertically into the air by with the Oklo or quasar results.
changing the frequency of the lasers and it passes The European Space Agency has plans to fly an
through a microwave cavity on its way up and also atomic-clock experiment – called the Atomic Clock
on its way down as it falls under gravity. The whole Ensemble in Space (ACES) – on the International
process is then repeated. Space Station. In addition to various tests of
Another laser beam is used to make the atoms general relativity, ACES will be 100 times more
fluoresce, and the amount of fluorescence is sensitive to changes in α than terrestrial
measured as a function of the microwave experiments. ACES will comprise two atomic clocks:
frequency to plot a “resonance curve”. An a cesium clock called PHARAO (see photograph)
ultra-precise measurement of time can be made built by a team led by Christophe Salomon of the
by measuring the frequency of the peak in this ENS and Andre Clairon of the Observatoire de Paris,
resonance curve (see “Atomic clocks” by and a hydrogen maser built by Alain Jornod of the
Pierre Lemonde in Physics World January 2001 Observatoire Cantonal de Neuchâtel in Switzerland.
pp39–44). The ACES experiment is particularly exciting for
It turns out that the width of the resonance curve my colleagues and me because it might be able to
is inversely proportional to the time that it takes for detect a drift in the value of α, which would confirm
the atoms to pass through the microwave cavity, so our quasar results. On the other hand, ACES may
the curve becomes narrower as the atoms spend find no change. However, this will not show that the
longer in the cavity. This allows the position of the quasar results are wrong because the two
peak to be determined more precisely, which experiments probe vastly different times and α
means that the clock becomes more accurate. could be changing at very different rates in these
This is why physicists are keen to place an atomic different epochs. Moreover, the rate of change
fountain in space: “micro-gravity” conditions will may also depend on other factors, such as the
extend the time by a factor of 10, with a local gravitational potential.
Prior to our work, α had been measured by looking at shift of the gas: λobs = (1 + z)λ, where z is the redshift and λ is
“alkali doublet” lines in systems such as singly ionized mag- the original wavelength.
nesium (Mg II). This ion has a single electron in its outer shell The change in the absorption spectrum caused by the red-
and its first excited energy level is split into a doublet as a shift and that caused by any change in α are different and
result of interactions between the orbital and spin angular can be separated out. Whereas the effect of the redshift is to
momenta of the electron. The energy difference between the multiply the wavelength of every line in the spectrum by the
two states in the doublet is proportional to α2. Indeed, “fine name number, 1 + z, any variation in α only changes the rel-
structure” is defined as the splitting of energy levels due to ative separation between the lines in the doublet.
interactions between the orbital and spin angular momenta. However, the alkali-doublet approach fails to take advant-
This fine-structure splitting means that Mg II absorbs light age of one crucial physical aspect. When an atom or ion is in
at two slightly different frequencies when it is excited from its its ground state, the electrons spend a lot more time close to
ground state to the first excited state. In the laboratory these the nucleus than they do when the atom is in an excited state.
wavelengths are 2796 Å and 2803 Å. The expansion of the Since α essentially defines the strength of the interaction be-
universe means that the wavelengths observed in quasar tween the nucleus and the electrons, any change in α will have
spectra, λobs, are longer by a factor that depends on the red- a greater impact on the atom or ion when in its ground state.
36 physicsweb.org PHYSICS WORLD APRIL 2003
5. 2 How spectral lines shift What could produce a spurious signal in the data?
AIII SiII We have spent a great deal of time and effort trying to answer this
SiII FeII NiII AI III Zn II Cr II Fe II Fe II Mg II Mg I question and make sure that the results we have seen are due to a
0
change in the value of α and not something else. We have even
written an entire paper summarising all the possible sources of error
and quantifying them one by one (see Murphy et al. in further
reading). After an exhaustive study we came up with only two possible
experimental effects that could significantly influence the results.
∆α/α
–0.5 One concerned the dispersion of light from the quasar as it
passed through the Earth’s atmosphere. Light at each end of the
optical spectrum is dispersed by a different amount, since the
refractive index of any medium depends on frequency.
A sophisticated application of what is high-school physics allows us
to compute the importance of this effect, with the conclusion that it
1.0
is unable to explain the results we find.
1500 2000 2500 3000 A second and more subtle effect concerns the relative amounts of
rest wavelength (Å) different isotopes of the same elements in the quasar spectra and
To check if the value of the fine-structure constant, α, has changed over the the laboratory spectra. Terrestrial samples of magnesium, for
history of the universe it is necessary to compare the wavelength of various
absorption lines in quasar spectra, after redshift effects have been removed, example, contain 79% magnesium-24, 10% magnesium-25 and
with the corresponding wavelengths as measured in the laboratory. The top 11% of magnesium-26. What if the gas clouds contain different
(green) line in this figure shows the position of various absorption lines in relative abundances of these isotopes? Again, we have looked at
atoms and ions of silicon (Si), iron (Fe), aluminium (Al), zinc (Zn), chromium this effect in detail and it is unable to explain the quasar results. In
(Cr) and magnesium (Mg) as measured in the laboratory. Mg I is neutral
magnesium, Mg II is singly ionized magnesium (i.e. a Mg+ ion) and so on. The fact, averaged over the whole quasar sample, we find that any
wavelengths of these lines depend on α in different ways, and the coloured attempt to include these effects in our interpretation of the quasar
lines show where the absorption lines would be if α was smaller in the past data is likely to make the results even more statistically significant.
than it is today. The red line corresponds to a value of α that is 90% of the
current value (i.e. ∆α/α = –0.1), green corresponds to 80%, and so on. Notice
how some atoms hardly change as α varies (e.g. silicon), whereas others shift
towards longer wavelengths (e.g. iron) or shorter wavelengths (zinc). This laboratory experiments to re-measure the wavelengths of all
observation is important because it means that it would be hard for effects the absorption lines seen in the quasar spectra. Much of this
other than a variation in α to mimic this pattern.
experimental work was carried out by Anne Thorne and
Juliet Pickering at Imperial College in London and the data
But the alkali-doublet method uses just a single atomic spe- are now so accurate that there is no longer a significant error
cies, so it measures change relative to the same ground state due to laboratory measurements in the quasar results.
and so misses out on this advantage. The observations have been carried out by many astron-
For these reasons, Victor, Vladimir Dzuba and I developed omers, including Chris Churchill of Penn State University,
a method to use different sets of atomic absorption lines and Jason Prochaska and Michael Rauch of the Carnegie Ob-
compare wavelengths relative to different ground states. After servatories in Pasadena, Art Wolfe of the University of Ca-
we realized that comparing laboratory and quasar observa- lifornia at San Diego, and Tom Barlow, Rob Simcoe and Wal
tions in this way would provide a huge increase in sensitivity, Sargent at the California Institute of Technology, while John
the challenge was to compute to a reasonable precision how Barrow at Cambridge has also been very active in the the-
the energy of an electron in its ground state changed for a oretical interpretation of the results. A great deal of work has
given change in α. Once we had that information, we could been done by Michael Murphy, who recently completed his
then translate any differences between the laboratory and PhD with me at UNSW and is now at Cambridge. Stephen
quasar measurements into a value for, or a upper limit on, any Curran and, very recently, Panayiotis Tzanivaris have also
possible change in the value of α. joined the project at UNSW.
A further advantage of this “many-multiplet” approach is Since the project started in 1998 we have measured 75
that light elements, such as magnesium, do not react strongly quasars at distances out to 13 billion light-years with the
to a change in α, whereas heavier elements such as iron do. 10 metre Keck 1 telescope on Hawaii. The results from the
This means that the light elements can be used as “anchors” Keck 1 data are astonishing. There is statistically significant
against which we can measure changes in heavier elements evidence that α may have been very slightly smaller in the
(figure 2). past, but only by about 1 part in 105 (see figure 3). We have ex-
However, when we first tried to apply the many-multiplet plored many different possible sources of errors but they can-
approach to real astrophysical data we got a big shock. The not explain what we find (see box on page 37).
high-resolution spectrographs on the world’s largest tele- We are aware, however, that all our data come from the
scopes were able to measure wavelengths in quasar spectra same instrument, the HIRES spectrograph on Keck 1, and
more accurately than they had ever been measured in the we are therefore keen to analyse data from other instruments
laboratory. In other words, we knew more about the fine and telescopes, such as the European Southern Observatory’s
structure of atoms 12 billion years ago than we did today, and magnificent Very Large Telescope (VLT). New quasar data
our efforts to look for changes in α were immediately limited are beginning to flow from the VLT – a set of four 8 metre
by the old experimental data. telescopes in Chile – and we should soon be able to tell whe-
It was therefore necessary to begin a series of brand new ther the same signal appears in those data.
PHYSICS WORLD APRIL 2003 physicsweb.org 37
6. 3 Results from quasar spectra What does it all mean?
It should be noted that the present status of all these ex-
periments is one of consistency. For example, the geological
0 results do not conflict with the quasar results or the atomic-
clock experiments because they probe very different epochs
∆α/α
–1
in the history of the universe. It is possible that the value of α
was changing relatively rapidly (by 1 part in 105) in the first
few billion years after the Big Bang, and that the fractional
–2 change has been 100 times smaller since the time of the Oklo
0 1 2 3
redshift reactor about two billion years ago. We cannot repeat the
When the fractional change in the fine-structure constant, ∆α/α, is plotted Oklo “experiment” but the results from the quasar observa-
as a function of redshift, we find that the value of α appears to have been tions and the atomic-clock experiments will become increas-
slightly smaller (by about 1 part in 105) in the past than it is now. Each of
the green data points in the figure corresponds to an average of about
ingly accurate over the next few years.
10 independent quasar measurements, and the redshifts range from z = 0.55 Confirmation that α is changing would have profound im-
(about 5.6 billion years ago) to z = 3 (about 12.6 billion years ago). If α was not plications for physics. For instance, the equivalence principle –
changing over the history of the universe then the data points would be one of the cornerstones of relativity – states that in freely fal-
scattered about the horizontal dashed line (see Webb et al. in further reading).
ling reference frames, the outcome of any non-gravitational
experiment is independent of when and where it is carried out.
Other groups are also joining the hunt. John Bahcall of the Changes in the value of α would constitute a violation of
Institute for Advanced Studies in Princeton and colleagues the equivalence principle. However, this is not necessarily bad
have just completed an exceptionally thorough analysis based news because many of the theories that seek to unify the four
on a new approach in which they studied oxygen emission lines fundamental forces of nature also violate the equivalence prin-
from distant galaxies. Although Bahcall and co-workers took ciple. The varying speed of light (VSL) theories, first proposed
enormous care to select only the highest quality data for their by John Moffat of the University of Toronto and developed in
analysis, the precision they finally reach is about an order of recent years by João Magueijo of Imperial College, John Bar-
magnitude less than we obtained using the many-multiplet row and others as an alternative to inflationary models in cos-
methods on quasar absorption spectra. This means that they mology, could also lead to changes in the value of α in the early
have not yet been able to provide a test of our results (see universe. Inflation and VSL theories are both attempts to ex-
further reading). plain various features of the universe – such as its apparent flat-
If the new data do not confirm the results so far, the com- ness – that cannot be explained by the Big Bang theory alone.
bined data from Keck 1 and the VLT will nevertheless place If the quasar results are eventually confirmed, our concepts
the most stringent constraints so far on the form that new uni- of space and time are sure to undergo radical transforma-
fied theories of the fundamental forces must take. And if the tions. Who knows how this will change our fundamental un-
new data support a changing α, we may eventually have to re- derstanding of the universe?
write significant portions of modern physics.
Further reading
The early universe J N Bahcall, C L Steinhardt and D Schlegel 2003 Does the fine-structure
We can also search for variations in α at even earlier times constant vary with cosmological epoch? arXiv.org/abs/astro-ph/0301507
in the history of the universe. If we change α, we change the J Barrow 2002 The Constants of Nature (Jonathan Cape, London)
temperature at which electrons and protons recombined in J D Bekenstein 2003 Fine-structure constant variability: surprises for
the early universe to form neutral hydrogen atoms: this is the laboratory atomic spectroscopy and cosmological evolution of quasar spectra
process that defines the formation of the cosmic microwave arXiv.org/abs/astro-ph/0301566
background about 380 000 years after the Big Bang (see L Bergström, S Iguri and H Rubinstein 1999 Constraints on the variation of the
“The cosmic microwave background” by Pedro G Ferreira fine-structure constant from big bang nucleosynthesis Phys. Rev. D 60 045005
on page 27 and Martins et al. in further reading). A change in C J A P Martins et al. 2003 WMAP constraints on varying α and the promise of
α would change the time at which recombination occurred, reionization arXiv.org/abs/astro-ph/0302295
and this could be detected by satellite measurements of the H Marion et al. 2003 A search for variations of fundamental constants using
cosmic background. atomic fountain clocks arXiv.org/abs/physics/0212112
The formation of light elements such as helium, deuterium M T Murphy et al. 2002 Does the fine-structure constant vary? A detailed
and lithium in the first few minutes after the Big Bang would investigation into systematic effects arXiv.org/abs/astro-ph/0210532
also be affected if α was changing over time. The equations K A Olive et al. 2002 Constraints on the variations of the fundamental
that define the rate at which the light elements are formed are couplings arXiv.org/abs/hep-ph/0205269
modified in different ways if α varies over time. This means J-P Uzan 2002 The fundamental constants and their variation: observational
that accurate measurements of the relative abundances of status and theoretical motivations arXiv.org/abs/hep-ph/0205340
these elements can also be used to constrain any change in α J K Webb et al. 2001 Further evidence for cosmological evolution of the
over almost the entire history of the universe – from the first fine-structure constant Phys. Rev. Lett. 87 091301
few minutes after the Big Bang until today (see Bergström et al. J K Webb et al. 2002 Does the fine-structure constant vary? A third quasar
in further reading). absorption sample consistent with varying alpha arXiv.org/abs/
Both of these methods are not yet very accurate. Neverthe- astro-ph/0210531
less they provide important complementary constraints on
any variations of α and show that it cannot have changed by John Webb is in the School of Physics, University of New South Wales, Sydney,
much more than 10% in either case. NSW 2052, Australia, e-mail jkw@bat.phys.unsw.edu.au
38 physicsweb.org PHYSICS WORLD APRIL 2003