Gravitational and LIGO

§ Gravitational waves § Detection of GW’s § The LIGO project and its sister projects § Astrophysical sources "Colliding Black Holes" § LIGO search for GWs National Center for Supercomputing Applications (NCSA) § Conclusions

Alan Weinstein, Caltech

AJW, CERN, July 14, 2004 The of

Newton’s Theory “instantaneous

Gmn= 8pTmn

Einstein’s General Gravity is a local property of the

occupied by m1. 2 Information carried F = m1 a = G m1 m2 / r / / by gravitational at the AJW, CERN, July 14, 2004 of Gravitational Waves

Static gravitational fields are described in as a curvature or warpage of space-time, changing the distance between space-time events. Shortest straight-line path of a nearby test-mass is a ~Keplerian . If the source is moving (at close to c), eg, because it’s orbiting a companion, the “news” of the changing propagates outward as gravitational radiation – a of curvature

AJW, CERN, July 14, 2004 Einstein’s Theory of Gravitation experimental tests

bending of light Mercury’s orbit “Einstein Cross” As it passes in the vicinity perihelion shifts forward The bending of light rays of massive objects twice Post-Newton theory gravitational lensing

First observed during the solar Mercury's elliptical path around the image appears around the eclipse of 1919 by Sir Arthur shifts slightly with each orbit central glow formed by nearby Eddington, when the Sun was such that its closest point to the Sun galaxy. Such gravitational lensing silhouetted against the Hyades (or "perihelion") shifts forward images are used to detect a ‘dark cluster with each pass. ’ body as the central object

AJW, CERN, July 14, 2004 Strong-field

•Most tests of GR focus on small deviations from Newtonian dynamics (post-Newtonian weak-field approximation) •Space-time curvature is a tiny effect everywhere except: ØThe in the early moments of the ØNear/in the horizon of black holes •This is where GR gets non-linear and interesting! •We aren’t very close to any black holes But we can search for (weak-field) (fortunately!), and can’t see them with light gravitational waves as a signal of their presence and dynamics

AJW, CERN, July 14, 2004 Nature of Gravitational Radiation

General Relativity predicts that rapidly changing gravitational fields produce ripples of curvature in the fabric of h = DL / L spacetime •transverse space-time distortions, freely propagating at • mass of = 0 • Stretches and squeezes space between “test ” – strain h = DL/L • GW are tensor fields (EM: vector fields) two polarizations: plus (Å) and cross (Ä) (EM: two polarizations, x and y ) Contrast with EM dipole radiation: of graviton = 2 )) •Conservation laws: • cons of Þ no monopole radiation xˆ (( )) yˆ

• cons of Þ no dipole radiation )) • lowest multipole is wave (spin 2)

AJW, CERN, July 14, 2004 Sources of GWs

§ Accelerating charge Þ electromagnetic radiation (dipole) § Accelerating mass Þ gravitational radiation (quadrupole) § of the gravitational wave (dimensional analysis): 2G 4p 2GMR2 f 2 h = I&& Þ h » orb mn c4r mn c4 r § && = second derivative Imn of mass quadrupole moment (non-spherical part of – tumbling dumb-bell) § G is a small number! § Need huge mass, relativistic km velocities, nearby. § For a binary pair, 10m light-years away, solar masses moving at 15% of speed of light: Terrestrial sources TOO WEAK!

AJW, CERN, July 14, 2004 Contrast EM and GW information

E&M GW space as medium for field Space-time itself incoherent superpositions of , molecules coherent motions of huge masses (or energy)

small compared to sources - wavelength ~large compared to sources - images poor spatial resolution absorbed, scattered, dispersed by matter very small interaction; no shielding

106 Hz and up 103 Hz and down

measure amplitude (radio) or intensity (light) measure amplitude

detectors have small solid angle acceptance detectors have large solid angle acceptance

• Very different information, mostly mutually exclusive • Difficult to predict GW sources based on E&M observations • GW is a totally new and unique window on the universe AJW, CERN, July 14, 2004 Observing the Galaxy with Different Electromagnetic http://antwrp.gsfc.nasa.gov/apod/ image/SagSumMW_dp_big.gif l = 5 x 10 -7 m

http://antwrp.gsfc.nasa.gov/apod /image/xallsky_rosat_big.gif l = 5 x 10 -10 m http://antwrp.gsfc.nasa.gov/apod /image/comptel_allsky_1to3_big.gif l = 6 x 10 -13 m

http://www.gsfc.nasa.gov/astro/cobe l = 2 x 10 -6 m

http://cossc.gsfc.nasa.gov/cossc/ egret/ //rsd-www.nrl.navy.mil/7213/lazio/GC/ l = 1 x 10 -14 m l = 9 x 10 -1 m AJW, CERN, July 14, 2004 What will we see?


AJW, CERN, July 14, 2004 Gravitational wave detectors

• Bar detectors • Invented and pursued by Joe Weber in the 60’s • Essentially, a large “bell”, set ringing (at ~ 900 Hz) by GW • Only discuss briefly, here – See EXPLORER at CERN! • Michelson interferometers • At least 4 independent discovery of method: • Pirani `56, Gerstenshtein and Pustovoit, Weber, Weiss `72 • Pioneering by Weber and Robert Forward, in 60’s • Now: large, -based detectors. Soon: space-based (LISA).

AJW, CERN, July 14, 2004 Resonant bar detectors

§ AURIGA bar near Padova, (typical of some ~5 around the world – Maryland, LSU, Rome, CERN, UWA) § 2.3 tons of Aluminum, 3m long; § Cooled to 0.1K with dilution fridge in LiHe cryostat § Q = 4´106 at < 1K § Fundamental resonant mode at ~900 Hz; narrow bandwidth § Ultra-low-noise capacitive transducer and electronics (SQUID)

AJW, CERN, July 14, 2004 Resonant Bar detectors around the world

International Gravitational (IGEC)

Baton Rouge, Legarno, CERN, Frascati, Perth, LA USA Italy Suisse Italy Australia

AJW, CERN, July 14, 2004 Interferometric detection of GWs

GW acts on freely mirrors falling masses: laser

Beam For fixed ability to splitter Dark port measure DL, make L photodiode P = P sin2 (2kDL) as big as possible! out in

Antenna pattern: (not very directional!)

AJW, CERN, July 14, 2004 LIGO – the first Km- class GW detector

L - DL L + DL

AJW, CERN, July 14, 2004 International network

Simultaneously detect signal (within msec) GEO Virgo § detection LIGO TAMAconfidence § locate the sources

§ verify light speed propagation

§ decompose the of gravitational waves

AIGO §Open up a new field of ! AJW, CERN, July 14, 2004 LIGO, VIRGO, GEO, TAMA …


LLO TAMA 4K 300 VIRGO 3000

AJW, CERN, July 14, 2004 Event Localization With An Array of GW Interferometers


LIGO Hanford LIGO Livingston


cosq = dt / (c D12) Dq ~ 0.5 deg t/c d L = D q 1 D 2 AJW, CERN, July 14, 2004 The Laser Interferometer Space Antenna LISA

Three spacecraft in orbit The center of the triangle formation about the sun, will be in the ecliptic plane with 5 million km baseline 1 AU from the Sun and 20 degrees behind the Earth.

LISA (NASA/JPL, ESA) may fly in the 10 years! AJW, CERN, July 14, 2004 Sensitivity bandwidth

§ EM waves are studied over ~20 orders of magnitude » (ULF radio -> HE g rays)

§ Gravitational Waves over ~10 orders of magnitude » (terrestrial + space)

AJW, CERN, July 14, 2004 LIGO Observatories

Hanford (LHO) : 4 km (H1) two interferometers in same + 2 km (H2) envelope

4 km L1 Both sites are relatively Livingston (LLO): seismically quiet, one interferometer low human noise AJW, CERN, July 14, 2004 Interferometer Concept

§ Laser used to measure § Arms in LIGO are 4km relative lengths of two § Measure difference in length to orthogonal arms one part in 1021 or 10-18 meters

Power recycling mirror sends…causing reflected the light back in,interference coherently, to be reused As a wave pattern to change Suspendedpasses, the at the photodiode armMasses lengths change in different ways….

Seismic Isolation AJW, CERN, July 14, 2004 Stacks Interferometer Noise Limits

Seismic Noise test mass (mirror) At present, noise in the LIGO detectors is dominated by “technical” sources, Residual gas associated with as-yet-imperfect implementation of the design

Quantum Noise

Residual gas scattering Radiation pressure "Shot" noise

LASER Beam Wavelength & splitter amplitude Thermal fluctuations (Brownian) photodiode AJW, CERN, July 14, 2004 Noise Commissioning and the First Runs

1999 2000 2001 2002 2003 2004 3Q 4Q 1Q 2Q 3Q 4Q 1Q 2Q 3Q 4Q 1Q 2Q 3Q 4Q 1Q 2Q 3Q 4Q 1Q 2Q 3Q

Inauguration First Lock Full Lock all IFO's Now strain noise density @ 200 Hz [Hz-1/2] 10-17 10-18 10-19 10-20 10-21 10-22

E1 E2 E3 E4 E5 E6 E7 E8 E9 E10 Engineering Runs S1 S2 S3 Science S4® First Science Data

AJW, CERN, July 14, 2004 Sensitivity in 3 Science Runs

S1 1st Science Run end Sept. 2002 17 days

S2 2nd Science Run end Apr. 2003 59 days LIGO Target Sensitivity

S3 3rd Science Run end Jan. 2004 64 days AJW, CERN, July 14, 2004 LIGO schedule

1995 NSF funding secured ($360M) 1996 Construction Underway (mostly civil) 1997 Facility Construction (vacuum system) 1998 Interferometer Construction (complete facilities) 1999 Construction Complete (interferometers in vacuum) 2000 Detector Installation (commissioning subsystems) 2001 Commission Interferometers (first coincidences) 2002 Sensitivity studies (initiate LIGO I Science Run) 2003+ LIGO I data run (one year integrated data at h ~ 10-21)

2007… Begin Advanced LIGO upgrade installation 2008… Begin Advanced LIGO observations…

AJW, CERN, July 14, 2004 Improvement of reach with Advanced LIGO

Improve amplitude sensitivity by a factor of 10x, and… Þ Number of sources goes up 1000x! Virgo cluster


AJW, CERN, July 14, 2004 Astrophysical Sources of Gravitational Waves

§ Compact binary systems » Black holes and neutron » Inspiral ® merger ® ringdown » Probe internal structure, nuclear eqn of state of NS crust, populations, and spacetime geometry § Spinning neutron stars » known & unknown » LMXBs » Probe internal structure and populations § Neutron star birth » core collapse » Instabilities: tumbling, convection » Correlations with EM observations Analog from cosmic § Stochastic background » Big bang & other early universe background -- » Background of GW bursts AJW, CERN, July 14, 2004 WMAP 2003 GWs from coalescing compact binaries (NS/NS, BH/BH, NS/BH)

Compact binary mergers

AJW, CERN, July 14, 2004 Binary Orbit

§ A binary system in a close orbit has a time-varying quadrupole moment è emits gravitational waves

fGW = 2 forbit Gravitational waves carry away energy and dE/dt µ -f 10 / 3 è increases, orbit shrinks df /dt µ f 11/3 dr/dt µ -f 2 Objects spiral in until they finally coalesce Additional relativistic effects kick in as (Gm/rc2) grows away from zero AJW, CERN, July 14, 2004 Hulse-Taylor binary

Neutron Binary System PSR 1913 + 16 -- Timing of pulsars

17 / sec · • A rapidly spinning pulsar (neutron star beaming EM radiation at us 17 x / sec) • orbiting around an ordinary star with 8 hour period • Only 7 kpc away · • discovered in 1975, orbital parameters ~ 8 hr measured • continuously measured over 25 years!

AJW, CERN, July 14, 2004 GWs from Hulse-Taylor binary

emission of gravitational waves by compact binary system

§ Only 7 kpc away § period speeds up 14 sec from 1975-94 § measured to ~50 msec accuracy § deviation grows quadratically with time § Merger in about 300M years § (<< age of universe!) § shortening of period Ü orbital energy loss § Compact system: § negligible loss from friction, material flow § beautiful agreement with GR prediction § Apparently, loss is due to GWs! § Nobel Prize, 1993

AJW, CERN, July 14, 2004 Chirp signal from Binary Inspiral

determine •distance from the earth r •masses of the two bodies •orbital eccentricity e and orbital inclination I •Over-constrained parameters: TEST GR AJW, CERN, July 14, 2004 The sound of a chirp

BH-BH collision, no noise

The sound of a BH-BH collision, Fourier transformed over 5 one-second intervals (red, blue, magenta, green, purple) along with expected IFO noise (black)

AJW, CERN, July 14, 2004 Astrophysical sources: Thorne diagrams

LIGO I (2002-2005)

LIGO II (2007- )

Advanced LIGO

AJW, CERN, July 14, 2004 Estimated detection rates for compact binary inspiral events



V. Kalogera (population synthesis)

AJW, CERN, July 14, 2004 Supernova collapse sequence

§ Within about 0.1 second, the core collapses and gravitational waves Gravitational waves are emitted. § After about 0.5 second, the collapsing envelope interacts with the outward shock. are emitted. § Within 2 hours, the envelope of the star is explosively ejected. When the reach the surface of the star, it brightens by a factor of 100 million. § Over a period of months, the expanding remnant emits X-rays, visible light and radio waves in a decreasing fashion.

AJW, CERN, July 14, 2004 Gravitational Waves from Supernova collapse

Non axisymmetric collapse ‘burst’ signal

Rate 1/50 yr - our galaxy 3/yr - Virgo cluster

AJW, CERN, July 14, 2004 Zwerger-Müller SN waveforms

§ astrophysically-motivated waveforms, computed from of axi-symmetric SN core collapses. § Almost all waveforms have duration < 0.2 sec § A “menagerie”, revealing only crude systematic regularities. Inappropriate for matched filtering or other model-dependent approaches. » Their main utility is to provide a set of signals that one could use to compare the efficacy of different filtering techniques. § Absolute normalization/distance scale.

AJW, CERN, July 14, 2004 Pulsars and continuous wave sources

§ Pulsars in our galaxy »non axisymmetric: 10-4 < e < 10-6 »science: neutron star precession; interiors »“R-mode” instabilities »narrow band searches best

AJW, CERN, July 14, 2004 Gravitational waves from Big Bang

Cosmic microwave background

AJW, CERN, July 14, 2004 GWs probe the universe at earliest times after the Big Bang

AJW, CERN, July 14, 2004 LIGO limits and expectations on WGW

LIGO S1 data 2 Cryo Bars S1 result: WGW < 23 0 S2 prelim: W < 0.02 -2 GW S3 expect: W <~ 10-3 -4 GW Cosmic strings LIGO, 1 yr data ]

gw -6 LIGO design, 1 year:

W Pulsar [ W <~ 10-5 - 10-6 10 GW -8

Log Adv. LIGO, 1 yr Advanced LIGO, 1 year:

-10 LISA -9 CMBR String WGW <~ 10 phase transition -12

-14 Challenge is to slow-roll limit identify and -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 eliminate noise Log [ f (Hz) ] 10 correlations between H1 and H2! AJW, CERN, July 14, 2004 Frequency-Time Characteristics of GW Sources • Bursts are short duration, broadband events time • Chirps explore the greatest time- frequency area

Ringdowns • BH Ringdowns expected to be associated with chirps Broadband Background • CW sources have FM characteristics which depend on

Bursts position on the sky (and source

frequency CW (quasi-periodic) parameters) • Stochastic background is stationary and broadband Chirps

• For each source, the optimal signal to noise ratio is obtained Earth’s orbit by integrating signal along the Earth’s rotation trajectory df •If SNR >> 1, kernel µ |signal|^2 » 2.6 ´10-4 df •If SNR < 1, kernel µ f » 4 ´10 -6 |template* signal| or |signal* signal | frequency f j k

frequency •Optimal filter: time kernel µ 1/(noise ) time AJW, CERN, July 14, 2004 Ultimate Goals for the Observation of GWs

§ Tests of Relativity – speed (delays in arrival time of bursts) – Spin character of the radiation field (polarization of radiation from CW sources) – Detailed tests of GR in P-P-N approximation (chirp waveforms) – Black holes & strong-field gravity (merger, ringdown of excited BH) § Gravitational Wave Astronomy (observation, populations, properties): – Compact binary inspirals – Gravitational waves and burst associations – formation – Supernovae in our galaxy – Newly formed neutron stars - spin down in the first year – Pulsars and rapidly rotating neutron stars – LMXBs – Stochastic background

AJW, CERN, July 14, 2004 Einstein’s Symphony

§ Space-time of the universe is (presumably!) filled with vibrations: Einstein’s Symphony § LIGO will soon ‘listen’ for Einstein’s Symphony with gravitational waves, permitting » Basic tests of General Relativity » A new field of astronomy and astrophysics § A new window on the universe!

AJW, CERN, July 14, 2004