Searching for lumbering giants slides

Searching for Nanohertz Gravitational Waves
with a Galactic-Scale Detector
Jeffrey S. Hazboun,
University of Washington Bothell
Funded under NSF Award 1430284
Jeffrey Hazboun (North City) The Search for Lumbering Giants 3 May 2021 1 / 47

The Cosmos as we know it.
Light has been our
messenger!
Cyg- A
Bullet Cluster
Sun SN 1987 A
Carina Nebula
Arp 78 Moon

Photons as Messengers
A myriad of instruments exist to
detect photons, but photons are
limited by the fact that they
interact readily with matter and
only astrophysical mechanisms
that emit light can be seen.

Gravity as Messenger
Don’t look with light, look with gravity.
Gravitational Waves are complementary to photons.
Photons are made by atoms.
Gravitational waves are made by the dynamic motion of matter.

General Relativity
Can not reconcile Special
Relativity with Newtonian
gravity.
Special Relativity: Nothing can
travel faster than light.
Gravity cannot travel faster
than light!
The curvature of spacetime is
gravity...

Particles follow curved lines when spacetime is curved

Of Course It’s Only an Analogy

General Relativity & the Einstein Field Equation
Spacetime = Matter & Energy
Curvature Content
Matter tells spacetime
how to curve.
Spacetime tells matter
how to move.

Any Questions??

Gravitational Waves are Dynamic Curvature

How do we detect Gravitational Waves?
- If you want to detect a physical phenomenon, you ask yourself
“What does is do to a physical system?”
- Gravitational waves change the proper spacetime distance between points.
1 2
3 4
1 2
3 4
1 2
3 4

Sounds of the Cosmos: Circular vs. Eccentric

How Strong are Gravitational Waves?
h =
∆L
L
- Couple Dancing h ∼ 2×10−54

h =
∆L
L
- Battleships Colliding
h ∼ 5×10−46

h =
∆L
L
h ∼ 5×10−46
- Io Orbiting Jupiter h ∼ 3×10−25

h =
∆L
L
h ∼ 5×10−46
- NS Binary at Galactic Center
h ∼ 2×10−19

h =
∆L
L
h ∼ 5×10−46
- NS Binary at Galactic Center
h ∼ 2×10−19
- SMBH Binary at Cosmological
Distance h ∼ 1×10−15

Help!
Water Speed
Speed of Sound

How to detect this motion? Interferometers!

LIGO
LIGO – Hanford, WA
LIGO – Livingston, LA

LIGO Detected the first signal from a Black Hole Binary
On September 14th, 2015 (∼ 30M⊙)

LIGO Detected the first signal from a Neutron Star Binary in 2017

LASER Interferometric Space Antenna
◦ 5 Million km Arms
◦ LISA Pathfinder has
vastly outperformed
its goals.

Inside LISA Pathfinder

Any Questions??

Searching for Lumbering Giants
◦ It’s been a good few years for
people interested in black holes.
◦ Binary black holes are the
bread & butter signals for LIGO.
◦ The 2020 Nobel Prize in Physics was
given for work on black holes.
◦ The silhouette of the SMBH at the
center of M87 was captured by
the Event Horizon Telescope.
◦ Mass calculated from this image is
6.5 billion M⊙.
◦ Most galaxies have a black hole at their
center.
◦ Need a much bigger detector to see
supermassive binary black holes.

Image Credit: Event Horizon Telescope Collaboration
◦ It’s been a good few years for
people interested in black holes.
◦ Binary black holes are the
bread & butter signals for LIGO.
◦ The 2020 Nobel Prize in Physics was
given for work on black holes.
◦ The silhouette of the SMBH at the
center of M87 was captured by
the Event Horizon Telescope.
◦ Mass calculated from this image is
6.5 billion M⊙.
◦ Most galaxies have a black hole at their
center.
◦ Need a much bigger detector to see

Pulsar Timing Arrays
- Millisecond Pulsars are the remnants of stars, ∼ 20km
across, spinning a thousand times per second.
- They are neutron stars that are inclined such that we can see
emission.
- Very stable clocks. Spin period of PSR J0437-4715:
P = 0.00575745193671259±0.000000000000000002s!
- Period of pulsar known to 1/1015

PTA: Galactic Scale Gravitational Wave Detector
Image Credit: Tonia Klein

PTA: Galactic Scale Gravitational Wave Detector
Image Credit: Tonia Klein Image Credit: David Nice

GW Interferometry vs Pulsar Timing Arrays
Similarities Differences
- Use light to measure the passage of GWs
- Sensitive to changes in distance proportional
to their respective “nuclei”
- Astronomy of Compact Objects
- Tests of Gravity/GR
- Seismic noise
- Shot noise / jitter
- Glitches
- Measure ∆L/L vs. ∆ν/ν
- Strongest source: CBCs vs. Stochastic
Background
- Evenly sampled data vs. Uneven PSR
observing cadence
- 9 orders of magnitude in frequency
- 8 orders of magnitude in strain
- (Knowledge of) Physics of light source

Continuous, Burst and Stochastic Signals
Continuous Wave Signal:
- Low to medium strength signal.
- Long lived.
- Few frequencies.
Burst Signal:
- Strong to medium strength signal.
- Short lived
- Many frequencies.

Continuous, Burst and Stochastic Signals
Stochastic Background:
- Individual sources weak,
but the sum is detectable.
- Long lived.
- Many frequencies.
Often following a power-law,
or turnover power spectral
model.
- Gerhard Mantz, Rough Seas

Stochastic Gravitational Wave Backgrounds
◦ Single gravitational wave sources are seen as
“rotating hourglasses”.
◦ Individual pulsars see sinusoidal signals in the
times-of-arrival of pulses.
◦ Single sources can be searched for using a
deterministic “matched-filter” analysis.
◦ Many individual sources add up to a stochastic
gravitational wave background (GWB).
◦ The characteristic strain from the GWB follows
a power law dependent on the population of
hc
¡
f
¢
= AGWB
µ
f
fyr
¶− 2
3

Spatial Correlations
0 20 40 60 80 100 120 140 160 180
Degrees of Separation on the Sky
−0.1
0.0
0.1
0.2
0.3
0.4
0.5
Correlation
The sky positions of our pulsars translate to a
correlation factor in the
correlation matrix of our analyses.
⋆ ◦ +
⋆
◦
+
−1.00
−0.75
−0.50
−0.25
0.00
0.25
0.50
0.75
1.00
Cartoon Correlation Matrix

⋆ ◦ +
⋆
◦
+
−1.00
−0.75
−0.50
−0.25
0.00
0.25
0.50
0.75
1.00
◦ Correlating data across
realistic pulsar data sets is
a bit messier.
◦ It takes looking at a lot of
pulsar pairs to average
out the noise.

Any Questions??

Super Massive Binary Black Hole Astrophysics
Black Hole / Host Galaxy Relationships Directed Searches (3C66B), Caitlin Witt
Middleton, et al., 2020. Massive black hole binary systems and the NANOGrav 12.5 year results
Aggarwal, et al., [Vigeland] 2019. Massive black hole binary systems and the NANOGrav 12.5 year results
Simon and Burke-Spolaor, 2016, Constraints on black hole/host galaxy co-evolution and binary stalling using pulsar
timing arrays

Multimessenger Astrophysics
Targeted Searches for Candidates SMBBH Candidates with LSST
“after 5 years of LSST observations, tens of true
binaries will be detectable”
Arzoumanian, et al., [Charisi] 2021 The NANOGrav 11yr Data Set: Limits on Supermassive Black Hole Binaries in
Galaxies within 500Mpc
Kelley, et al., 2019 Massive BH binaries as periodically variable AGN

Alternative Polarizations Nima Laal will be releasing new NANOGrav results very soon!
Neil Cornish, Logan O’Beirne, Steve Taylor, Sarah Vigeland
Cornish, et al., 2018, Constraining alternative theories of gravity using pulsar timing arrays
O’Beirne, et al., 2019, Constraining alternative polarization states of gravitational waves from individual black hole
binaries using pulsar timing arrays

Cosmic Strings
◦ Metastable cosmic strings from inflation
and cosmological phase transitions form a
stochastic GWB
◦ The colored blue (green) region accounts
for successful inflation, baryogenesis and
dark matter for the maximal (minimal)
allowed value of Gµ. The dashed red line
shows the spectrum for stable cosmic
strings for the best-fit value Gµ = 10−10
.
Buchmuller, Domcke and Schmitz, 2020. From NANOGrav to LIGO with metastable cosmic strings.
Blanco-Pillado, Olum, and Siemens, 2018. New limits on cosmic strings from gravitational wave observation.

Ultralight Scalar Field (Fuzzy) Dark Matter
◦ Hu, Barkana and Gruzinov, 2000 proposed
an ultralight scalar as an alternative to
standard CDM
◦ Oscillations in the Newtonian potential
change the frequency of millisecond
pulsations.
◦ Brendan Drachler & Michael Lam at RIT
working on dual signal recovery.
Porayko, et al., 2018. Parkes Pulsar Timing Array constraints on ultralight scalar-field dark matter.

Any Signal in the nanohertz band
◦ QCD matter confinement phase transition GWB
◦ Clumps of Dark Matter (Shapiro Delay, Doppler
Shifts)
◦ Primordial Black Holes
◦ Limits on mass of graviton
◦ The Astrophysics of Nanohertz Gravitational Waves,
arxiv:1811.08826
◦ Physics Beyond the Standard Model With Pulsar
Timing Arrays, arxiv:1907.04960

NANOGrav 12.5-Year Data Set: Common “Red” Process
Spectral analysis shows strong evidence for power at lowest frequencies.
Arzoumanian, et al., [Simon] 2021. The NANOGrav 12.5 yr Data Set: Search for an Isotropic Stochastic
Gravitational-wave Background

NANOGrav 12.5-Year Data Set: Spatial Correlations
◦ NG12.5 yr spatial correlations
◦ Note that, while the fit to the
Hellings-Downs curve is getting better, fits
to other curves are also reasonable.
◦ As individual pulsar become more
sensitive at lower frequencies we will get
more information about the spatial
correlations.
Arzoumanian, et al., [Simon] 2021. The NANOGrav 12.5 yr Data Set: Search for an Isotropic Stochastic
Gravitational-wave Background

NANOGrav Members at the Green Bank Telescope, WVa. Image Credit: Tonia Klein

Detection Prospects
Image Credit: C. M. F. Mingarelli, Underlying figure from Taylor, et al. 2016
Detection
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2026
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2021
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Very strong GWB; McWilliams et al. (2014)
Moderate GWB; Sesana (2013)
Stalled GWB; Ryu et al. (2018)
Less massive SMBHs; Sesana et al. (2016)
Minimum GWB; Bonetti et al. (2018)
GWB Floor
Burke-Spolaor, et al., 2019. The astrophysics of nanohertz gravitational waves.
The Astronomy and Astrophysics Review. arXiv:1811.08826

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