GRAVITATIONAL WAVES

Eanna E. FlanaganCornell University

Presentation to CAA, 30 April 2003 [Some slides provided by Kip Thorne]

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Summary of talk

l Review of observational upper limits and current and planned detectors.

l What are the science goals and opportunities of gravitational wave astronomy?

» Ground based / space based» Near term / long term

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Summary of Science Goals

l Probe gravity» Number of polarizations» Speed of waves» Mass of graviton» Frame dragging, tails …» Bound scalar couplings

l Neutron star physics» Nuclear equation of state» Formation dynamics» Measure ellipticity» Crust/core coupling

l Probe of black holes» Population studies: M,a» Map geometry» Nonlinear dynamics of gravity

l Cosmology» Measure energy scale of

inflation / disprove inflation» Probe dark energy?» Probe structure formation» Detect early Universe phase

transitions, cosmic strings, Goldstone modes…l Other

» Identify γ-ray burst sources?» Discover unexpected sources

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Physical Nature of Gravitational Waves

l Ripples of curvature in the fabric of spacetime

∆L / L = h

l Notation: ( )220

2

3crit 10100)ln(1

−

≈=Ω h

Hzf

xdfddE

ρ

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Overview of High Frequency Sources

l Neutron Star & Black Hole Binaries» inspiral» merger

l Spinning NS’s» LMXBs» known pulsars» previously unknown

l NS Birth (SN, AIC)» tumbling» convection

l Stochastic background» big bang» early universe

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Neutron Star / Neutron Star Inspiral(our most reliably understood source)

l 1.4 Msun / 1.4 MsunNS/NS Binaries

l Event rates » V. Kalogera et al,

astro-ph/0012038300 Mpc

l Advanced IFOs -» Range: 300Mpc » 1 / yr to 2 / day

~10 min

~3 sec

~10,000 cycles

20 Mpc

l Initial IFOs» Range: 20 Mpc» 1 / 3000 yrs to 1 / 3yrs

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l Relativistic effects are very strong -- e.g.» Frame dragging by spins ⇒ precession ⇒ modulation

» Measure wave tails, limit Branse-Dicke coupling, graviton mass

l Information carried:» Masses (a few %), Spins (?few%?), Distance [not redshift!] (~10%),

Location on sky (~1 degree)

– Mchirp = µ3/5 M2/5 to ~10-3

l Search for EM counterpart, e.g. γ-burst. If found: » Learn the nature of the trigger for that γ-burst

» deduce relative speed of light and gw’s to ~ 1 sec / 3x109 yrs ~ 10-17

Science From Observed Inspirals: NS/NS, NS/BH, BH/BH

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Neutron Star / Black Hole Inspiraland NS Tidal Disruption

l 1.4Msun / 10 MsunNS/BH Binaries

l Event rates » Population Synthesis

[Kalogera]650 Mpc

l Advanced IFOs» Range: 650 Mpc» 1 / yr to 4 / day<~

43 Mpc inspiralNS

disrupt

l Initial IFOs» Range: 43 Mpc» 1 / 2500 yrs to 1 / 2yrs<~

140 Mpc

Initial estimates suggestNS Radius measurable

to 15%; infer eqn of state

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Black Hole / Black Hole Inspiraland Merger

l 10Msun / 10 MsunBH/BH Binaries

l Event rates » Based on population

synthesis

z=0.4 inspiral

mergerl Advanced IFOs -

» Range: z=0.4 » 2 / month to ~10 / day<~

100 Mpc inspiral

merger

l Initial IFOs» Range: 100 Mpc» 1 / 300yrs to ~1 / yr<~

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BH/BH Mergers: Exploring the Dynamics of Spacetime Warpage

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Spinning NS’s: Pulsars

l Unknown NS’s - All sky search:» Sensitivity ~5 to 15

worse

l NS Ellipticity:» Crust strength ε

ε < 10-6; possibly 10-5

Crab SpindownUpper Limit

l Known Pulsars:» First Interferometers:

ε 3x10-6 (1000Hz/f)x (distance/10kpc)

» Narrowband Advanced

ε 2x10-8 (1000Hz/f)2

x (distance/10kpc)

>~

>~

ε = 10

-7 , 10kp

c

ε = 10

-6 , 10k

pc

ε = 10

-5 , 10kp

c

~

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Spinning Neutron Stars:Low-Mass X-Ray Binaries

Signal strengths for 20 days of integration

Sco X-1

l If so, and steady state: X-ray luminosity ⇒ GW strength

l Combined GW & EM

obs’s ⇒ information about:» crust strength & structure

l Rotation rates ~250 to 700 revolutions / sec» Why not faster?» Bildsten: Spin-up torque

balanced by GW emission torque

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Neutron Star Births: Tumbling Bar; Convection

l Born in:» Supernovae » Accretion-Induced Collapse of White Dwarf

l If slow spin:» Convection in first ~1 sec.» Advanced IFOs: Detectable only in our Galaxy

(~1/30yrs) » GW / neutrino correlations!

l If very fast spin:» Centrifugal hangup» Tumbling bar - episodic? (for a few sec or min)» If modeling gives enough waveform information,

detectable to:– Initial IFOs: ~5Mpc (M81 group, ~1 supernova/3yr)– Advanced IFOs: ~100Mpc (~500 supernovae/yr)

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Low Frequency Sources

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Waves from Very Early Universe

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Waves from Very Early Universe

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Early Universe Waves

l Sources» Parametric amplification:

inflation, bounce cosmologies» Preheating» Phase transitions» Cosmic strings» Kibble mechanism» Extra dimensions, branes..

l Observational Handles» Energy spectrum» Detection of bursts» Non-Gaussianity» Non-stationarity» Non-isotropy

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Sensitivity to Dark Energy?

l Require recent (z<=1-2) GW sources

l Coalescing binaries are standard candles:» LISA can measure luminosity distance to SMBH binaries to 1%» Combine with electromagnetic measurement of redshift» Subject to systemic errors due to lensing.

l Alternative method: time variation of redshifts» Loeb (1998) showed dz/dt encodes cosmological information» Sato et. Al. (2001) suggested LISA follow on mission could measure

dz/dt for many NS/NS binaries» Analog of lensing noise reduced by (v/c)^2.

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Conclusion: Science Goals

l Probe gravity» Number of polarizations» Speed of waves» Mass of graviton» Frame dragging, tails …» Bound scalar couplings

l Neutron star physics» Nuclear equation of state» Formation dynamics» Measure ellipticity» Crust/core coupling

l Probe of black holes» Population studies: M,a» Map geometry» Nonlinear dynamics of gravity

l Cosmology» Measure energy scale of

inflation / disprove inflation» Probe dark energy?» Probe structure formation» Detect early Universe phase

transitions, cosmic strings, Goldstone modes…l Other

» Identify γ-ray burst sources?» Discover unexpected sources