The Gravity Probe B experiment tested two predictions of general relativity using gyroscopes in a satellite orbiting Earth. It measured the geodetic precession and frame-dragging precession predicted by Einstein to within 0.2% and 18.4% accuracy, respectively, confirming his theory of gravitation. Technical challenges arose from the gyroscopes not being perfectly spherical, leading to greater errors than anticipated. The experiment was a decades-long effort involving NASA, Stanford University, and collaboration with other institutions.
Unstable/Astatic Gravimeters and Marine Gravity SurveyRaianIslamEvan
This is a descriptive article on stable and unstable gravimeters. The article is mainly focused on LaCoste-Romberg and Worden gravimeters. Also, it includes marine gravity survey shortly.
Definition
Geophysics is the application of method of physics to the
study of the earth.
On the other sense, it is a subject of natural science
concerned with the physical processes and the physical
properties of the earth and its surrounding space
environment and the use of co-ordinate methods for the
analysis.
It involves the application of physical theories and
measurements to discover the properties and processes of the
earth.
Unstable/Astatic Gravimeters and Marine Gravity SurveyRaianIslamEvan
This is a descriptive article on stable and unstable gravimeters. The article is mainly focused on LaCoste-Romberg and Worden gravimeters. Also, it includes marine gravity survey shortly.
Definition
Geophysics is the application of method of physics to the
study of the earth.
On the other sense, it is a subject of natural science
concerned with the physical processes and the physical
properties of the earth and its surrounding space
environment and the use of co-ordinate methods for the
analysis.
It involves the application of physical theories and
measurements to discover the properties and processes of the
earth.
A Gravity survey is an indirect (surface) means of calculating the density pr...Shahid Hussain
A Gravity survey is an indirect (surface) means of calculating the density property of subsurface materials. The higher the gravity values, the denser the rock beneath.
First discovery of_a_magnetic_field_in_a_main_sequence_delta_scuti_star_the_k...Sérgio Sacani
Coralie Neiner do Laboratory for Space Studies and Astrophysics Instrumentation, LESIA (CNRS/Observatoire de Paris/UPMC/Université Paris Diderot) e Patricia Lampens (Royual OIbservatory of Belgium), descobriram a primeira estrela magnética do tipo delta Scuti, através de observações espectropolarimétricas, realizadas com o telescópio CFHT. As estrelas do tipo delta Scuti, são estrelas pulsantes, sendo que algumas delas mostram assinaturas atribuídas para um segundo tipo de pulsação. A descoberta mostra que isso é na verdade a assinatura de um campo magnético. Essa descoberta tem importantes implicações para o entendimento do interior das estrelas.
Dois tipos de estrelas pulsantes existem entre as estrelas com massa entre 1.5 e 2.5 vezes a massa do Sol: as estrelas do tipo delta Scuti e as estrelas do tipo gamma Dor. A teoria nos diz que as estrelas com temperatura entre 6900 e 7400 graus Kelvin podem ter ambos os tipos de pulsação. Essas são então chamadas de estrelas híbridas. Contudo, o satélite Kepler da NASA tem detectado um grande número de estrelas híbridas com temperaturas maiores ou menores do que esse limite pensado anteriormente. A existência dessas estrelas híbridas com temperaturas maiores é algo muito controverso, já que desafia o nosso entendimento sobre as estrelas pulsantes do tipo delta Scuti e gamma Dor.
IOSR Journal of Applied Physics (IOSR-JAP) is an open access international journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
Variability in a_young_lt_transition_planetary_mass_objectSérgio Sacani
Padrões climáticos num misterioso mundo além do nosso Sistema Solar tem sido revelado pela primeira vez, sugere um estudo.
Camadas de nuvens, feitas de poeira quente e gotículas de ferro derretido, foram detectadas num objeto parecido com um planeta descoberto a 75 anos-luz de distância da Terra, dizem os pesquisadores.
As descobertas poderiam melhorar a habilidade dos cientistas de descobrir se condições em planetas distantes seriam capazes de sustentar a vida.
Uma equipe de pesquisadores liderada pela Universidade de Edimburgo, usou um telescópio no Chile para estudar o sistema climático de um mundo distante, conhecido como PSO J318.5-22, que estima-se tenha cerca de 20 milhões de anos de vida.
Os pesquisadores capturaram centenas de imagens infravermelhas do objeto enquanto ele rotacionava em torno do seu próprio eixo num período de 5 horas. Comparando o brilho do PSO J318.5-22, com corpos vizinhos, a equipe descobriu que ele era coberto por múltiplas camadas de nuvens finas e espessas. Essas nuvens causaram as mudanças no brilho do mundo distante enquanto ele executava o seu movimento de rotação, dizem os cientistas.
PROBING THE SOLAR INTERIOR WITH LENSED GRAVITATIONAL WAVES FROM KNOWN PULSARSSérgio Sacani
When gravitational waves (GWs) from a spinning neutron star arrive from behind the Sun, they are
subjected to gravitational lensing that imprints a frequency-dependent modulation on the waveform.
This modulation traces the projected solar density and gravitational potential along the path as
the Sun passes in front of the neutron star. We calculate how accurately the solar density prole
can be extracted from the lensed GWs using a Fisher analysis. For this purpose, we selected three
promising candidates (the highly spinning pulsars J1022+1001, J1730-2304, and J1745-23) from the
pulsar catalog of the Australia Telescope National Facility. The lensing signature can be measured
with 3 condence when the signal-to-noise ratio (SNR) of the GW detection reaches 100 (f=300Hz)1
over a one-year observation period (where f is the GW frequency). The solar density prole can be
plotted as a function of radius when the SNR improves to & 104.
A Gravity survey is an indirect (surface) means of calculating the density pr...Shahid Hussain
A Gravity survey is an indirect (surface) means of calculating the density property of subsurface materials. The higher the gravity values, the denser the rock beneath.
First discovery of_a_magnetic_field_in_a_main_sequence_delta_scuti_star_the_k...Sérgio Sacani
Coralie Neiner do Laboratory for Space Studies and Astrophysics Instrumentation, LESIA (CNRS/Observatoire de Paris/UPMC/Université Paris Diderot) e Patricia Lampens (Royual OIbservatory of Belgium), descobriram a primeira estrela magnética do tipo delta Scuti, através de observações espectropolarimétricas, realizadas com o telescópio CFHT. As estrelas do tipo delta Scuti, são estrelas pulsantes, sendo que algumas delas mostram assinaturas atribuídas para um segundo tipo de pulsação. A descoberta mostra que isso é na verdade a assinatura de um campo magnético. Essa descoberta tem importantes implicações para o entendimento do interior das estrelas.
Dois tipos de estrelas pulsantes existem entre as estrelas com massa entre 1.5 e 2.5 vezes a massa do Sol: as estrelas do tipo delta Scuti e as estrelas do tipo gamma Dor. A teoria nos diz que as estrelas com temperatura entre 6900 e 7400 graus Kelvin podem ter ambos os tipos de pulsação. Essas são então chamadas de estrelas híbridas. Contudo, o satélite Kepler da NASA tem detectado um grande número de estrelas híbridas com temperaturas maiores ou menores do que esse limite pensado anteriormente. A existência dessas estrelas híbridas com temperaturas maiores é algo muito controverso, já que desafia o nosso entendimento sobre as estrelas pulsantes do tipo delta Scuti e gamma Dor.
IOSR Journal of Applied Physics (IOSR-JAP) is an open access international journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
Variability in a_young_lt_transition_planetary_mass_objectSérgio Sacani
Padrões climáticos num misterioso mundo além do nosso Sistema Solar tem sido revelado pela primeira vez, sugere um estudo.
Camadas de nuvens, feitas de poeira quente e gotículas de ferro derretido, foram detectadas num objeto parecido com um planeta descoberto a 75 anos-luz de distância da Terra, dizem os pesquisadores.
As descobertas poderiam melhorar a habilidade dos cientistas de descobrir se condições em planetas distantes seriam capazes de sustentar a vida.
Uma equipe de pesquisadores liderada pela Universidade de Edimburgo, usou um telescópio no Chile para estudar o sistema climático de um mundo distante, conhecido como PSO J318.5-22, que estima-se tenha cerca de 20 milhões de anos de vida.
Os pesquisadores capturaram centenas de imagens infravermelhas do objeto enquanto ele rotacionava em torno do seu próprio eixo num período de 5 horas. Comparando o brilho do PSO J318.5-22, com corpos vizinhos, a equipe descobriu que ele era coberto por múltiplas camadas de nuvens finas e espessas. Essas nuvens causaram as mudanças no brilho do mundo distante enquanto ele executava o seu movimento de rotação, dizem os cientistas.
PROBING THE SOLAR INTERIOR WITH LENSED GRAVITATIONAL WAVES FROM KNOWN PULSARSSérgio Sacani
When gravitational waves (GWs) from a spinning neutron star arrive from behind the Sun, they are
subjected to gravitational lensing that imprints a frequency-dependent modulation on the waveform.
This modulation traces the projected solar density and gravitational potential along the path as
the Sun passes in front of the neutron star. We calculate how accurately the solar density prole
can be extracted from the lensed GWs using a Fisher analysis. For this purpose, we selected three
promising candidates (the highly spinning pulsars J1022+1001, J1730-2304, and J1745-23) from the
pulsar catalog of the Australia Telescope National Facility. The lensing signature can be measured
with 3 condence when the signal-to-noise ratio (SNR) of the GW detection reaches 100 (f=300Hz)1
over a one-year observation period (where f is the GW frequency). The solar density prole can be
plotted as a function of radius when the SNR improves to & 104.
O centro da nossa Via Láctea é um lugar misterioso. Não somente está a milhares de anos-luz de distância, mas está também escondido sob grande quantidade de poeira de modo que a maior parte das estrelas em seu interior são invisíveis. Pesquisadores de Harvard, estão propondo uma nova maneira de limpar a neblina e registrar as estrelas ali escondidas. Eles sugerem observar os comprimentos de onda de rádio provenientes das estrelas supersônicas.
“Existem muitas, nós não sabemos sobre o centro galáctico, e nós queremos aprender muito”, disse o principal autor do estudo Idan Ginsburg do Harvard-Smithsonian Center for Astrophysics (CfA). “Usando essa técnica, nós podemos encontrar estrelas que ninguém observou antes”.
A grande trajetória do centro da nossa galáxia para a Terra é repleta de tanta poeira que até mesmo dos trilhões de fótons de luz visível que veem em nossa direção, somente um fóton atingirá nossos telescópios. Ondas de rádio, de uma diferente parte do espectro eletromagnético, possui energia mais baixa e comprimentos de onda maiores. Elas podem passar pela poeira de forma ilesa.
A new universal formula for atoms, planets, and galaxiesIOSR Journals
In this paper a new universal formula about the rotation velocity distribution of atoms, planets, and galaxies is presented. It is based on a new general formula based on the relativistic Schwarzschild/Minkowski metric, where it has been possible to obtain expressions for the rotation velocity - and mass distribution versus the distance to the atomic nucleus, planet system centre, and galactic centre. A mathematical proof of this new formula is also given. This formula is divided into a Keplerian(general relativity)-and a relativistic(special relativity) part. For the atomic-and planet systems the Keplerian distribution is followed, which is also in accordance with observations.
According to the rotation velocity distribution of the galaxies the rotation velocity increases very rapidly from the centre and reaches a plateau which is constant out to a great distance from the centre. This is in accordance with observations and is also in accordance with the main structure of rotation velocity versus distance from different galaxy measurements.
Computer simulations were also performed to establish and verify the rotation velocity distributions in the atomic – planetary- and galaxy system, according to this paper. These computer simulations are in accordance with observations in two and three dimensions. It was also possible to study the matching percentage in these calculations showing a much higher matching percentage between theoretical and observational values by this new formula.
Probing the innermost_regions_of_agn_jets_and_their_magnetic_fields_with_radi...Sérgio Sacani
Desde 1974, observações feitas com o chamado Long Baseline Interferometry, ou VLBI, combinaram sinais de um objeto cósmico recebidos em diferentes rádio telescópios espalhados pelo globo para criar uma antena com o tamanho equivalente à maior separação entre elas. Isso fez com que fosse possível fazer imagens com uma nitidez sem precedentes, com uma resolução 1000 vezes melhor do que Hubble consegue na luz visível. Agora, uma equipe internacional de astrônomos quebrou todos os recordes combinando 15 rádio telescópios na Terra e a antena de rádio da missão RadioAstron, da agência espacial russa, na órbita da Terra. O trabalho, liderado pelo Instituto de Astrofísica de Andalucía, o IAA-CSIC, forneceu novas ideias sobre a natureza das galáxias ativas, onde um buraco negro extremamente massivo engole a matéria ao redor enquanto simultaneamente emite um par de jatos de partículas de alta energia e campos magnéticos a velocidades próximas da velocidade da luz.
Observações feitas no comprimento de onda das micro-ondas são essenciais para explorar esses jatos, já que os elétrons de alta energia se movendo em campos magnéticos são mais proficientes em produzir micro-ondas. Mas a maioria das galáxias ativas com jatos brilhantes estão a bilhões de anos-luz de distância da Terra, de modo que esses jatos são minúsculos no céu. Desse modo a alta resolução é essencial para observar esses jatos em ação e então revelar fenômenos como as ondas de choque e a turbulência que controla o quanto de luz é produzida num dado tempo. “Combinando pela primeira vez rádio telescópios na Terra com rádio telescópios no espaço, operando na máxima resolução, tem permitido que a nossa equipe crie uma antena que tem um tamanho equivalente a 8 vezes o diâmetro da Terra, correspondendo a 20 micro arcos de segundo”, disse José L; Gómez, o líder da equipe no Instituto de Astrofísica de Andalucía, IAA-CSIC.
The Population of the Galactic Center Filaments: Position Angle Distribution ...Sérgio Sacani
We have examined the distribution of the position angle (PA) of the Galactic center filaments with lengths L > 66″ and
<66″ as well as their length distribution as a function of PA. We find bimodal PA distributions of the filaments, and
long and short populations of radio filaments. Our PA study shows the evidence for a distinct population of short
filaments with PA close to the Galactic plane. Mainly thermal, short-radio filaments (<66″) have PAs concentrated
close to the Galactic plane within 60° < PA < 120°. Remarkably, the short filament PAs are radial with respect to the
Galactic center at l < 0° and extend in the direction toward Sgr A*
. On a smaller scale, the prominent Sgr E H II
complex G358.7-0.0 provides a vivid example of the nearly radial distribution of short filaments. The bimodal PA
distribution suggests a different origin for two distinct filament populations. We argue that the alignment of the shortfilament population results from the ram pressure of a degree-scale outflow from Sgr A* that exceeds the internal
filament pressure, and aligns them along the Galactic plane. The ram pressure is estimated to be 2 × 106 cm−3 K at a
distance of 300 pc, requiring biconical mass outflow rate 10−4 Me yr−1 with an opening angle of ∼40°. This outflow
aligns not only the magnetized filaments along the Galactic plane but also accelerates thermal material associated with
embedded or partially embedded clouds. This places an estimate of ∼6 Myr as the age of the outflow.
1. Gravity Probe B and Relativistic Precession
Presentation by Reece Boston
Oct 19, 2012
2. Introduction to Experiment
The Gravity Probe B Relativity Mission, fifty-year-long effort of
Stanford University, collaboration with NASA and Marshall
Space Flight Center
Experimental preparation started in1960 with Schiff and
Fairbank, spacecraft launched in Aug, 2004, data collection
finished Aug, 2005, data published 2011
Gyroscopes in drag-free satellite pointed at distant star HR8703
Tests two predictions of GR:
Geodetic Precession : Related to curvature of spacetime due
only to mass of earth. Two sources, “Gravitoelectric” just from
potential, and another due to space curvature.
Frame-Dragging : Related to the curvature due to mass-current
of spinning earth. Called “Gravitomagnetic”
Both effects very minute, even in conditions of experiment; order
of arcsecond/year.
This necessitates very accurate measuring devices.
3. Whence Precession?
Result of “fictitious torques” due to curvature of spacetime.
Consider familiar frustration of derivatives in 2D polar
coordinates.
Divergence in Cartesian components is
· F(r) =
∂
∂x
,
∂
∂y
· (Fx , Fy ) =
∂Fx
∂x
+
∂Fy
∂y
.
EASY!
So in polar components, with = ( ∂
∂r , 1
r
∂
∂φ )
· F(r) =
∂
∂r
,
1
r
∂
∂φ
· (Fr , Fφ) =
∂Fr
∂r
+
1
r
∂Fφ
∂φ
.
EASY! but WRONG!
Vectors can only be compared at the same point. Derivative
compares vectors at different points.
4. Whence Precession?
In taking divergence, we have terms of form
lim
→0
ˆn(r + u ) · F(r + u) − ˆn(r) · F(r)
= lim
→0
ˆn(r + u) − ˆn(r)
· F + ˆn ·
F(r + u ) − F(r)
.
To do the subtraction, we need to properly move the vector
F(r + u ) from its home at r + u , and put it at r.
This is called Parallel Transport: vector maintains same
orientation relative to u.
Because unit vectors will change, the components will change.
To first order in , change is linear
F(r + u )|| transport to r = F(r + u )at r + ˆeαΓα
βγFβ
uγ
The Γα
βγ are given by
Γα
βγ =
1
2
gαδ ∂gβδ
∂xγ
+
∂gγδ
∂xβ
−
∂gβγ
∂xδ
.
5. Whence Precession?
Consider particle on trajectory r = w(λ), with velocity u = ˙w.
How does v(r) change?
Directional derivative uv(r) =
v(r+udλ)||−v(r)
dλ .
Parallel transported v(r + udλ)|| = v(r + λu)at r + ˆeαΓα
βγvβuγ .
Hence, change in vector along trajectory is
uν
νvµ
=
∂vµ
∂xν
uν
+ Γµ
αβvα
uβ
.
If v = u, then uu = a and Γα
βγuβuγ is effective force.
Since Γα
βγ = 1
2gαδ ∂gβδ
∂xγ +
∂gγδ
∂xβ −
∂gβγ
∂xδ , metric coefficients are
effective potentials.
If uv = 0, then v is parallel-transported along trajectory w(λ).
A “geodesic” defines local inertial frame, follows trajectory
uu = 0.
6. Whence Precession?
So if a gyro is spinning with initial spin four-vector s = (0, s),
and moving on geodesic, uu = 0, then in its own rest frame s
remains space-like, u · s = 0.
Hence, s is parallel transported along trajectory defined by
four-velocity u, us = 0.
Gives gyroscopic equation
dsα
dτ
+ Γα
βγuγ
sβ
= 0.
Changed by effective “torques” from Christoffel symbols, in
analogy to ds
dt = Ω × s from classical mechanics.
These “torques” come from Γα
βγ, hence from gµν, hence related
to the curvature of spacetime.
Let’s find the precession terms!
7. Gravitoelectromagnetism
We now split metric tensor gαβ in to three parts
gravitoelectric scalar potential Φ = −c2
2 (g00 + 1)
gravitomagnetic vector potential γ = g0j ˆej
space curvature tensor gjk
We can define gravitoelectric field g = − Φ
We can define gravitomagnetic field H = × γ.
We can even define “Maxwell Equations” for these [c.f.
Braginsky, Caves, Thorne 1977]
· g = −4πGρ × g = 0
· H = 0 × H = 4[−4πGρv/c + (1/c)(∂g/∂t)]
From analogy to EM then, for spinning, spherical earth
g = −
GM
r2
ˆr and H =
2G
c
L − 3(L · ˆr)ˆr
r3
H will cause frame-dragging, g and gjk will cause geodesic
effect.
8. Frame-Dragging Precession
Gryoscope has spin s; this is a spinning clump of mass, or a
gravitomagnetic dipole, moment µ = 1
2s.
Magnetic dipole-dipole interaction experiences torque µ × B.
Earth-Gyroscope interaction is dipole-dipole, so s experiences
torque ds
dt = s
2 × H
c . [Thorne, 1988]
So precession due to gravitomagnetic effect is
ΩGM = −
1
2c
H =
G
c2
3(ˆr · L)ˆr − L
r3
.
9. Gravitoelectric Precession
Gravitomagnetic dipole experiences no torque from a stationary
gravitoelectric field , but an orbiting dipole sees an orbiting
Earth.
In electrodynamics, this produces induced magnetic field
Binduced = −v
c × E.
So we have induced gravitomagnetic field Hinduced = −v
c × g.
As above, this results in torque s × Hinduced
2c and precession
ΩGE = −
1
2c
Hinduced =
GM
2c2r2
ˆr × v.
10. Space Curvature Precession
So far all these effects have direct parallels in EM; however, the
3-tensor term gjk has no parallel.
gjk contains information on how space is curved due to the mass
monopole M – not spacetime curvature, but space curvature.
Can be visualized with example of vector on cone [c.f. Thorne]
Turns out to be ΩSC = 2ΩGE .
So total precession Ω = 3GM
2c2r2 ˆr × v + G
c2
3(ˆr·L)ˆr−L
r3 .
11. Experimental Set-Up
William Fairbank said:
“No mission could be simpler than GP-B: It’s just a star, a
telescope, and a spinning sphere.”
The Star:
Named HR8703, or IM Pegasi, optical and radio-star
Chosen for its brightness, its location near equator, highly
determinable proper motion [Buchman, et al., 2000]
Uncertainties in proper motion of star directly related to
experimental uncertainty [Mester, et al.,2004]
Motion of HR8703 is determinable because it is radio-star, able to
use Very-Long-Baseline Interferometry [Shapiro, et al., 2012]
Harvard Smithsonian Astronomical Observatory in separate
experiment established 0.1 marcsec/yr proper motion
uncertainties.
The Telescope:
The Spinning Sphere:
12. Experimental Set-Up
William Fairbank said:
“No mission could be simpler than GP-B: It’s just a star, a
telescope, and a spinning sphere.”
The Star:
The Telescope:
Set to track HR8703; provides “inertial” direction for comparison
to spin direction of gyroscope
Housed in atmosphere-drag-free satellite system; essentially an
exterior case that absorbs all shocks from collisions and
rebalances with very precise thrusters.
Makes realistic approximate local inertial frame. [c.f. Hartle,
2003]
[Hartle, Gravity, 2003 pg. 181]
The Spinning Sphere:
13. Experimental Set-Up
William Fairbank said:
“No mission could be simpler than GP-B: It’s just a star, a
telescope, and a spinning sphere.”
The Star:
The Telescope:
[Hartle, Gravity, 2003 pg. 181]
The Spinning Sphere:
14. Experimental Set-Up
William Fairbank said:
“No mission could be simpler than GP-B: It’s just a star, a
telescope, and a spinning sphere.”
The Star:
The Telescope:
The Spinning Sphere:
Have won Guinness World Record for most-perfectly spherical
objects ever.[Blau 2011]
Peak-to-valley asphericity of 25 nm, compared to 1.9 cm radius;
about 1 part per million asphericity.[Mester 2004]
Spin axes of gyros needs to be perfectly aligned with principal
axes of rotation
Made of fused quartz, coated in niobium for superconduction,
kept at 1.8K
Electrostatically suspended and positioned inside quartz housing
Coupled to SQUID magnetometer, which reads magnetic moment
of sphere
15. Experimental Set-Up
William Fairbank said:
“No mission could be simpler than GP-B: It’s just a star, a
telescope, and a spinning sphere.”
The Star:
The Telescope:
The Spinning Sphere:
17. How’d They Do?
Einstein predicts Geodetic Precession 6.606 arcec/year,
Framedragging Precession 0.0392 arcsec/year. [Everitt 2011]
Results show Geodetic Precession 6.602 ± 0.018 and
Frame-dragging Precession 0.0372 ± 0.0072 [Blau 2011]
Experiment confirms Geodetic to 0.2% and Frame-dragging to
18.4%; were hoping for 0.01% and 1%.
Gyros were not perfect spheres, so spin axis and principal axis
did not align perfectly. Caused more error than anticipated.
Tests still confirm Einstein’s predictions.