Gravitational and LIGO

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

Alan Weinstein, Caltech

AJW, CERN, August 4, 2005 The of

Newton’s Theory “instantaneous

Gmn= 8pTmn

Einstein’s General Gravity is a local property of the occupied by m 1 , curved by the source mass m 2 . Information about changing gravitational 2 F = m/ 1 a = G m/ 1 m2 / r field is carried by gravitational AJW, CERN, August 4, 2005at the 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, August 4, 2005 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, August 4, 2005 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 (fortunately!), and can’t see them with light But we can search for (weak-field) gravitational waves as a signal of their presence and dynamics

AJW, CERN, August 4, 2005 Nature of Gravitational Radiation

General Relativity predicts that rapidly changing gravitational fields produce ripples of curvature h = DL / L in the fabric of 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) Contrast with EM dipole radiation:

(EM: two polarizations, x and y ) )) of graviton = 2 xˆ (( )) yˆ

• Conservation laws: ))

• cons of Þ no monopole radiation • cons of Þ no dipole radiation AJW, CERN, August 4, 2005 • lowest multipole is wave (spin 2) 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!


The history of : new bands of the EM spectrum opened ® major discoveries! GWs aren’t just a new band, they’re a new spectrum, with very different and complementary properties to EM waves. • Vibrations of space-time, not in space-time • Emitted by coherent motion of huge masses moving at near light-speed; not vibrations of in • Can’t be absorbed, scattered, or shielded. GW astronomy is a totally new, unique window on the universe

AJW, CERN, August 4, 2005 What will we see?

GWs from the most energetic processes in the universe!

• black holes orbiting each other and then merging together • , GRBs • rapidly spinning neutron • Vibrations from the Big Bang

A NEW WINDOW ON THE UNIVERSE Analog from cosmic WILL OPEN UP FOR EXPLORATION. background -- WMAP 2003 BE THERE! AJW, CERN, August 4, 2005 GWs from coalescing compact binaries (NS/NS, BH/BH, NS/BH)

Compact binary mergers

AJW, CERN, August 4, 2005 Hulse-Taylor binary

Neutron Binary System PSR 1913 + 16 -- Timing of

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, August 4, 2005 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, August 4, 2005 Chirp signal from Binary Inspiral

determine •distance from the r •masses of the two bodies •orbital eccentricity e and orbital inclination I •Over-constrained parameters: TEST GR AJW, CERN, August 4, 2005 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, August 4, 2005 Astrophysical sources: Thorne diagrams

LIGO I (2002-2005)

LIGO II (2007- )

Advanced LIGO

AJW, CERN, August 4, 2005 Estimated detection rates for compact binary inspiral events



V. Kalogera (population synthesis)

AJW, CERN, August 4, 2005 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, August 4, 2005 Gravitational Waves from Supernova collapse

Non axisymmetric ‘burst’ waveforms core collapse (Type II supernovae)

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

Zwerger & Muller, 1997 & 2003 AJW, CERN, August 4, 2005simulations of axi-symmetric SN core collapse 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, August 4, 2005 Gravitational waves from Big Bang

13.7 billion 380,000 YEARS YEARS

cosmic microwave background -- WMAP 2003

AJW, CERN, August 4, 2005 LIGO limits and expectations on WGW

LIGO S1 data 2 Cryo Bars S1 result: WGW < 23 0 S2 result: W < 0.02 -2 GW S3 result: W < 8´10-4 -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, August 4, 2005 -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, August 4, 2005 Ultimate Goals for the Observation of GWs

§ Tests of Relativity – speed (delays in arrival time of bursts) – Spin character of the radiation field ( 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, August 4, 2005 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, earth-based detectors. Soon: space-based (LISA).

AJW, CERN, August 4, 2005 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, August 4, 2005 Resonant Bar detectors around the world

International Gravitational (IGEC)

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

AJW, CERN, August 4, 2005 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, August 4, 2005 LIGO – the first Km- class GW detector

L - DL L + DL

AJW, CERN, August 4, 2005 International network

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

§ verify light speed propagation

§ decompose the polarization of gravitational waves

AIGO §Open up a new field of ! AJW, CERN, August 4, 2005 LIGO, VIRGO, GEO, TAMA …


LLO TAMA 4K 300 VIRGO 3000

AJW, CERN, August 4, 2005 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, August 4, 2005 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, August 4, 2005 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, August 4, 2005 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, August 4, 2005 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, August 4, 2005 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 & splitter amplitude Thermal fluctuations (Brownian) photodiode AJW, CERN, August 4, 2005 Noise Despite a few difficulties, runs started in 2002.

AJW, CERN, August 4, 2005 Science Runs A Measure of Progress VirgoAndromeda Cluster NN Binary Inspiral Range

4/02: E8 ~ 5 kpc

10/02: S1 ~ 100 kpc

4/03: S2 ~ 0.9Mpc

11:03: S3 ~ 3 Mpc

Design~ 18 Mpc

AJW, CERN, August 4, 2005 Best Performance to Date ….

Current: all three detectors are within a factor of 2 of design sensitivity from ~ 50 Hz up!

AJW, CERN, August 4, 2005 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) 2003-4 LIGO I data runs (S1, S2, S3, S4) 2005+ LIGO I data run (one year integrated data at h ~ 10-21)

2004 Advanced LIGO approved by the NSB 2007… Begin Advanced LIGO upgrade installation 2010… Begin Advanced LIGO observations…

AJW, CERN, August 4, 2005 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, August 4, 2005 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, August 4, 2005