Gravitational wave astronomy

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Gravitational waveastronomy
Emanuele Berti, Washington University in Saint
Louis Ole Miss, October 10, 2006
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OutlineGravitational wavesExperimentsExpected
astrophysical sourcesPhysics with supermassive
black holes
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Gravitationalwaves
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The nature of gravity Newton and Einstein

• Newton
• Action at a distance
• Newtons Law describes effect of gravity but
  does not explain it
• Einstein
• Gravity is spacetime curvature
• Spacetime tells matter how to move, and matter
  tells spacetime how to curve

• Any mass-energy bends spacetime near it freely
  falling objects follow the local background
  curvature

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What are gravitational waves?
Any moving mass generates ripples in spacetime
curvature propagating at the speed of light away
from the source gravitational waves Unique
probes of spacetime curvature

• Gravitational waves stretch and squeeze
  alternately.
• The effect is opposite in perpendicular
  directions.
• Two independent polarization states (plus and
  cross)

• Never significantly absorbed or scattered
• Hard to detect
• Complementary observations of strong gravity
  regions not trasparent to EM waves
• We detect wave amplitudes h1/r, not energy
  fluxes Fh2(1/r)2
• Enhancement by a factor 2 in detector
  sensitivity increases visible volume by 8

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The gravitational wave spectrum

(Sathyaprakash)
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How strong are gravitational waves?
Leading-order approximation (quadrupole
formula)
Can we generate detectable gravitational waves on
Earth?
frot1 kHz h(2.6 x 10-33 m)/r rdistance from
detector gt ?? 3x105 m h lt 9 x 10-39
Astrophysical sources in relativistic
motion M1033 g, vc3 x 1010 cm/s, r15
Mpc5x1025 cm, h10-21 Experimental task
measure distance deviations of order DLhL10-21
(105 cm) 10-16 cm
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Experiments
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Testing gravity
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Indirect detection the Hulse-Taylor pulsar
1993 Nobel Prize to Hulse and Taylor discovery
of the binary pulsar 191316 Observations
consistent with predicted loss of energy due to
gravitational radiation
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A worldwide network of detectors
Also spherical detectors Sfera (Frascati),
MiniGRAIL (Leiden), Mario Schenberg (São Paulo)
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The early years resonant-mass detectors

• Present
• Five cryogenic bars taking data
• ALLEGRO (US),
• AURIGA (Italy),
• EXPLORER (CERN),
• NAUTILUS (Italy),
• NIOBE (Australia)

First gravitational wave detector Joseph Webers
aluminum bar (room temperature!)

• Still relatively narrow bandwidths, less
  sensitive than interferometers
• Collaboration to search for coincident bursts
• Spherical detectors (eg. MiniGRAIL) peak
  sensitivity 3kHz

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Interferometric detectors
Interferometers ideal for the quadrupolar nature
of gravitational waves send laser beams in
perpendicular directions and combine them on
return to construct interference patterns.
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A worldwide network of detectors
Various Earth-based interferometers are already
operational or in the commissioning phase

• LIGO (Livingston and Hanford, USA)two 4km and
  one 2km detector
• GEO (near Hannover, Germany/UK) 0.6km, LIGO
  partner
• Virgo (near Pisa, Italy/France) 3km
• AIGO (near Perth, Australia) 80m
• TAMA (near Tokyo, Japan) 0.3km

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Some impressive progress
Seismic noise
Advanced LIGO 2013, real GW astronomy!
Photon shot noise
From the LIGO Annual Review Report by the NSF
(Nov 9-11, 2005)All three instruments have
achieved, and slightly surpassed, the design
requirement ..LIGO is now ready for, and in
fact has just started, an extended observing run
with the goal of obtaining a full years worth
of coincident data at design sensitivity
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The future LISA
The Laser Interferometer Space Antenna is a joint
ESA-NASA spaceborne GW observatoryLaunch
planned around 2016 (?) 3 spacecraft in
heliocentric trajectory trailing 20 behind the
Earth Equilateral triangle, armlength L5x106
kml sensitive to 10-4 Hz lt f lt 1 Hz More
massive, stronger astrophysical sources Orbital
modulation allows determination of the source
position in the sky
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Digging out signals matched filtering
Looking for a needle in a haystack
(Plot from a LIGO seminar by P. Shawhan) Need
theory and/or numerical relativity simulations to
provide accurate templates
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Expected astrophysicalsources
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Low- and high-f binary coalescence

• Inspiral Post-Newtonian theory Phase of the
  wave known up to order O(v7)
• Merger Numerical relativity Last year
  breakthrough!
• Many groups can now evolve the last orbits of
• binary black holes
• throughout merger
• Ringdown Black hole perturbation
  theory Superposition of exponentially decaying
  sinusoids (quasinormal modes)

(Kip Thorne)
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High-f sources neutron stars
Supernova Accretion-induced WD collapse Bar
instability
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Low- and high-frequency sources
(Schutz)
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High-frequency sources (LIGO)

• NS/BH binaries
• BH-BH
• NS-NS
• NS-BH
• Spinning NSs
• NS Birth
• Supernovae
• AIC
• Stochastic
• Big Bang
• Early Universe

(Cutler Thorne 2002)
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Low-frequency sources (LISA)

• Galactic binaries
• Resolved (calibration)
• Unresolved (noise)
• EMRIs/IMRIs
• 100,000 cyclesin last year map the
  spacetimeof a rotating BH
• SMBH binaries
• Cosmological
• Standard inflation signal too weak
• Cosmic strings? (Damour Vilenkin) - Phase
  transitions? (Randall Servant)

(Larson, 33rd SLAC Summer School, 2005)
Waves from an Extreme Mass Ratio Inspiral
(Animation by Jonathan Gair)
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Physics with supermassive black holes
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The SMBH at the center of our Galaxy
(Movie courtesy of Reinhard Genzel and Steve
Drasco)
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LISA SNR for inspiral and ringdown
10000 _at_ z0.54
300 _at_ z10
(EB, Cardoso Will 06)
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SMBH merger history Msource(z), Jsource(z)
LISA only measures redshifted combinations of
masses and spins of the form M(1z)Msource
J(1z)2Jsource Measuring luminosity distance
DL(z,cosmology) and assuming cosmology is known,
find z(DL) and remove degeneracy
Luminosity distance Angular resolution
(steradians) Reduced mass Chirp mass
(EB, Buonanno Will 05)
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Testing alternative theories graviton mass
Solar system bound (Yukawa-type deviations from
Keplers third law) lg3x1012 km
DL3 Gpc (z0.5)
(EB, Buonanno Will 05)
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GR tests from ringdown waves

• One-mode detection
• Measure of black holes mass and angular
  momentum
• (Echeverria 89, Finn 92)

• Multi-mode detection
• First mode yields (M,j)
• In GR, quasinormal frequencies depend only on M
  and j
• second mode yields test that we are observing
  a rotating black hole
• Under reasonable assumptions, the test requires
  SNR10-100
• (EB, Cardoso Will 06)
• Test similar in nature to multipolar mapping
  with EMRIs

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Further reading

• Introduction at popular/undergraduate level
• K.S. Thorne, Black Holes and Time Warps
  Einsteins outrageous legacy
• J.B. Hartle, Gravity An Introduction to
  Einsteins General Relativity
• Gravitational wave sources and data analysis,
  introduction to LISA science
• C. Cutler K. S. Thorne, An Overview of
  Gravitational Wave Sources, gr-qc/0204090
• L.P. Grishchuk et al., Gravitational Wave
  Astronomy, gr-qc/0008481
• S. Larson, LISA A Modern Astrophysical
  Observatory, SLAC 2005
• Observational evidence for astrophysical black
  holes
• R. Narayan, Black Holes in Astrophysics,
  gr-qc/0506078
• Status of experimental tests of general
  relativity
• C.M. Will, The Confrontation between General
  Relativity and Experiment,
• http//relativity.livingreviews.org/