Gravitational Waves and LIGO

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Gravitational Waves and LIGO Alan Weinstein,Caltech LIGO-G000167-00-R What is a gravitational wave? Where do they come from? What can we learn from them? How can we detect them? LIGO and its sister projects 2 bservatory O ravitational-Wave The LIGO Project Project LIGO AJW, Caltech, G nterferometer nterferometer I aser L » them to run laboratory ...and » LSC) Collaboration, Scientific » (LIGO Funded by the US National Science Foundation (NSF) US project to build observatories for gravitational waves (GWs) to enable an initial detection, then an astronomy of GWs collaboration by MIT, Caltech; other institutions participating Two sites separated by 3000 km each site carries 4km vacuum system, infrastructure interferometersof multiple (IFOs)capable each site establishment of a network with other interferometers of a variety GW searches for A facility lifetime of >20 years goal: best technology, to achieve fundamental noise limits for terrestrial IFOs LIGO-G000167-00-R LIGO: Observatory characteristics Evolution of interferometers in LIGO 3 in which “instantaneously” , law of gravitation

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Newtonian Gravity and ) static, unchanging arena F=ma are the time acts over large distances and laws of motion ( sun LIGO-G000167-00-R » comets of orbits eccentric » variations their of tides and cause » earth’s axis the of precession the » the of gravity by moon of the of the motion perturbation the »unified. Kepler and Copernicus Galileo, of Work the dynamics of planetary motion (and all other motion) do their thing Space Three (centripetal force) disparate phenomena Solved most known problems of astronomy and terrestrial physics are Gravitational fields static (or slowly changing), the force 4 )

E = mc geometry 2 (or

2 2

c Project LIGO AJW, Caltech,

−

2 Einstein and relativity

-(pc)

+dz 2 2 4D space-time 4D space-time

+dy = E

2 ⇒ 2 )

c = dx 0

ds (m LIGO-G000167-00-R • space+time •Distances in space and time change between in space and time •Distances observers moving relative to one another, but the invariant: interval remains space-time • between change also momentum and energy observers moving relative to one another, but the does not mass changeinvariant (rest) Special (1906): Relativity Enter Einstein! Enter • 5

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Space-time geometry Discards concept of absolute motion; instead treats only relative motion between systems space and time no longer viewed as separate; rather as four dimensional space-time gravity described as a warpage (curving) of space-time, not a force acting at a distance LIGO-G000167-00-R Relativity and space-time geometry: 6 2 r / 2 m 1 Gm = a 1 m space that the “test mass” occupies, occupies, “test mass” the that space = F time: Einstein’s

AJW, Caltech, LIGO Project LIGO AJW, Caltech, General Relativity (1916) Warped space- theory of gravity theory

geometric LIGO-G000167-00-R for gravity (as opposed to all other forces), motion (acceleration) depends only on location, not mass gravitational acceleration depends only on the geometry of the of the geometry the on only depends acceleration gravitational A Imagine space as a stretched rubber sheet. sheet. rubber stretched a as space Imagine a deformation. will cause surface the mass on A mass. will that toward roll sheet the onto dropped mass (“test”) Another are they because not masses, larger toward travel masses smaller that theorized Einstein the largerthe object. not any properties of the test mass itself mass test the of properties any not ½ travel objects smaller the because but distance, a across acts that a force by "attracted" is space through that by warped ½ 7 “Einstein Cross”

gravitational lensing central glow formed by nearby nearby by central glow formed images are used to detect a ‘dark a ‘dark detect to used are images The bending of light rays matter’ body as the central object matter’ body galaxy. Such gravitationalgalaxy. lensing Quasar image appears around the appears Quasar image with pass. each Mercury’s orbit experimental tests shifts slightly withshifts slightly each orbit twice Newton’s theory (or "perihelion") shifts forward perihelion shifts forward

AJW, Caltech, LIGO Project LIGO AJW, Caltech, such that its closest point to the Sun point closest its such that Mercury's elliptical path around the Sun Mercury's Einstein’s Theory of Gravitation cluster LIGO-G000167-00-R bending of light

of massive objects eclipse Sir of 1919 by Arthur Eddington, when the Sun was First observed during the solar First observed

As it passes in the vicinity silhouetted against the Hyades star 8 QFD theory QCD QED GR…? ) ) 0 ) G g γ , Z - , W + W Gluons ( Photon ( Graviton( Carried by (massive) (massless) (massless) (massless) “flavor” charge Color Electric charge Charge Mass Quarks, leptons Acts on Quarks Charged particles All particles

AJW, Caltech, LIGO Project LIGO AJW, Caltech, -2 -13 -40 Strength 10 10 10 10 Strength of gravitational force LIGO-G000167-00-R Gravitational force is very weak… Gravitational force is very it dominates! universe) stars, galaxies, scales (planets, But at large Interaction Strong nuclear Electromagnetic Weak nuclear Gravitational 9 ) weak-field But we can search for ( weBut can search of their waves as a signal gravitational dynamics and presence and AJW, Caltech, LIGO Project LIGO AJW, Caltech, effect effect tiny non-linear Strong-field The universe in the earlyin moments of The universe holes the horizon of black Near/in LIGO-G000167-00-R the big bang the big ½ ½ Most tests of GR focus on small deviations small GR focus on Most tests of is a curvature Space-time gets GR This is where holes black any close to We aren’t very interesting! • • • • from Newtonian dynamics dynamics from Newtonian approximation) weak-field (post-Newtonian with light (fortunately!), see them and can’t everywhere except: everywhere 10

Einstein’s Theory carried information by gravitational radiation at the speed of light

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Spacetime curvature Dynamics of changing

“instantaneous Newton’s Theory

action at a distance” LIGO-G000167-00-R

14 )) )) ˆ y (( )) ˆ x Contrast with EM dipole radiation:

AJW, Caltech, LIGO Project LIGO AJW, Caltech, ⇒ ⇒ ⇒ ) –strain –strain ⊗ Nature of Gravitational Radiation L/L space-time distortions, space-time distortions, ∆ two polarizations no dipole radiation no monopole radiation no monopole ) and cross ( ) and ⊕ h = propagating at speed of light propagating at speed •quadrupole 2) wave (spin •conservation of energy of energy •conservation LIGO-G000167-00-R •conservation of momentum of momentum •conservation plus ( transverse transverse Stretches and squashes space General predicts Relativity : • • masses” “test between laws: •Conservation freely freely 15 GW Hz and down 3 Space-time itself Space-time 10 measure amplitude measure poor spatial resolution spatial poor very small interaction; no shielding no interaction; small very wavelength ~large compared to sources - sources to compared ~large wavelength detectors have large solid angle acceptance angle solid large have detectors coherent motions of huge masses (or energy) (or masses huge of motions coherent

AJW, Caltech, LIGO Project LIGO AJW, Caltech, E&M Hz and up images 6 10 Contrast EM and GW information space as medium for for field as medium space • mostlyexclusive information, mutually different Very •E&M observations on predict GW sources based to Difficult wavelength small compared to sources - absorbed, scattered, dispersed by matter dispersed scattered, absorbed, measure amplitude (radio) or intensity (light) intensity or (radio) amplitude measure detectors have small solid angle acceptance angle solid small have detectors LIGO-G000167-00-R incoherent superpositionsincoherent molecules atoms, of ! 16 TOO WEAK 2 orb f Terrestrial sources Terrestrial 2 r 4 c GMR 2

π 4 electromagnetic radiation (dipole) gravitational radiation (quadrupole) Sources of GWs ≈ AJW, Caltech, LIGO Project LIGO AJW, Caltech, h ⇒ ⇒ ⇒

µν & & I r 4 G c 2 = second derivative =

µν µν & & is a small number! I h moving at 15% of speed of light: – tumbling dumb-bell) G Need huge mass, relativistic Amplitude of the gravitational wave (dimensional analysis): Accelerating mass Accelerating charge For a binary neutron star pair, 10m light-years away, solar masses of mass quadrupole moment (non-spherical part of kinetic energy velocities, nearby. LIGO-G000167-00-R 17

AJW, Caltech, LIGO Project LIGO AJW, Caltech, What will we see? LIGO-G000167-00-R 18 Astrophysical

AJW, Caltech, LIGO Project LIGO AJW, Caltech, neutron star) Sources of Gravitational Waves (rotating, beaming (rotating, beaming supernova collapse Non-axi-symmetric Non-axi-symmetric Non-axi-symmetric pulsar pulsar Non-axi-symmetric (neutron stars, black holes) Coalescing compact binaries binaries Coalescing compact LIGO-G000167-00-R 20

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Compact binary mergers Compact binary GWs from coalescing compact binaries (NS/NS, BH/BH, NS/BH) LIGO-G000167-00-R 21 LIGO II (2007- ) LIGO I (2002-2005) Advanced LIGO Thorne diagrams

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Astrophysical sources: LIGO-G000167-00-R 22

AJW, Caltech, LIGO Project LIGO AJW, Caltech, How far out can we see? LIGO-G000167-00-R Number of sources goes Number Improve amplitude sensitivity by a factor of 10x, and… ⇒ up 1000x! 23 LIGO II LIGO I Virgo cluster

AJW, Caltech, LIGO Project LIGO AJW, Caltech, How many sources can we see? LIGO-G000167-00-R Number of sources Number goes up 1000x! Improve amplitude sensitivity by a factor of 10x, and… ⇒ 24 • 17 / sec • ~ 8 hr Neutron Binary System Binary Neutron PSR 1913 + 16 -- Timing of pulsars

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Hulse-Taylor binary pulsar LIGO-G000167-00-R A rapidly spinningA pulsar (neutronstar Only 7 kpc away orbiting around an ordinary starwith discovered in 1975, orbital parameters continuously measured over 25 years! • beaming EM radiation at us 17 x / sec) • 8 hour period • • measured • 25

AJW, Caltech, LIGO Project LIGO AJW, Caltech, orbital loss energy ⇐ GWs from Hulse-Taylor binary LIGO-G000167-00-R (<< age of universe!) age of (<< flow friction, material negligible loss from emission of gravitational waves by compact binary system compactwaves binary by gravitational emission of Apparently, loss is due to GWs! to due is loss Apparently, Only 7 kpc 7 Only away Compact system: Nobel Prize, 1993 period speeds up 14 sec from 1975-94 measured~50 to msec accuracy deviation grows quadratically with time Merger in about 300M years shortening of period beautiful agreementwith GR prediction i 26 determine distance from the earth r the earth from distance bodies two of the masses e and orbital inclination orbital eccentricity • • •

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Chirp signal from Binary Inspiral LIGO-G000167-00-R 27 computer simulations Collision of two black holes Distortion of space-time black hole a by

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Black holes: Testing General Relativity in the Strong Field Limit Testing General Relativity LIGO-G000167-00-R “Grand Challenge” – “Grand Challenge” Project Supercomputer 28

Optical Light Curve Optical

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Supernova collapse

The Collapse LIGO-G000167-00-R 29 Within about 0.1 second, the core collapses and gravitational waves are emitted. After about 0.5 second, the interacts with collapsing envelope the outward shock. Neutrinos are emitted. Within 2 hours, the envelope of the star is explosively ejected. When the photons 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, and light radio waves in a visible decreasing fashion.

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Gravitational waves Gravitational Supernova collapse sequence LIGO-G000167-00-R 30 Rate Tycho’s Supernova, Supernova, Tycho’s - Supernava Kepler’s - Crab Supernava The in Centaurus in the SN 1604 SN1054 SN 1572 SN1006 within Virgo Cluster ~ 3 / year ~ 3 / Cluster within Virgo our galaxy our galaxy years 1/50 +other possible Milky Way Way Milky possible +other studied in detail by Tycho Brahe Tycho by in detail studied supernovae southern sky Chinese by recorded in Taurus American astronomers and Native

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Historical Supernova (our galaxy) LIGO-G000167-00-R

Kepler SNR Crab Nebula Crab Nebula 1054 AD 32 ‘burst’ signal

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Supernova collapse Gravitational Waves from Rate

3/yr - cluster Virgo 1/50 yr - our galaxy LIGO-G000167-00-R Non axisymmetric collapse 33 LIGO

AJW, Caltech, LIGO Project LIGO AJW, Caltech, astrophysical sources SN1987A LIGO-G000167-00-R 34 < 10-6 ε non axisymmetric: 10-4 < science: neutron star precession; interiors instabilities “R-mode” narrow band searches best » » » » Pulsars in our galaxy

AJW, Caltech, LIGO Project LIGO AJW, Caltech,

Pulsars and continuous wave sources LIGO-G000167-00-R 37

Cosmic

microwave background microwave

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Gravitational waves from Big Bang LIGO-G000167-00-R 38

AJW, Caltech, LIGO Project LIGO AJW, Caltech, times after the Big Bang GWs probe the universe at earliest LIGO-G000167-00-R 39 Scales

AJW, Caltech, LIGO Project LIGO AJW, Caltech, LIGO-G000167-00-R 40

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Gravitational wave detectors • Invented and pursued by Joe Weber in the 60’s • by GW ~ 900 Hz) (at ringing set “bell”, Essentially, a large • here any Won’t discuss further, • At least 4 independent discovery of method: • Pirani `56, Gerstenshtein and Pustovoit,• `72 Weber, Weiss 60’s in Forward, Robert and Weber by work Pioneering Bar detectors Michelson interferometers LIGO-G000167-00-R • • 41 –

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Resonant bar detectors at < 1K < at 6 10 × AURIGA bar near Padova, Italy Padova, near AURIGA bar long; 3m of Aluminum, 2.3 tons with dilution fridge 0.1K Cooled to in LiHe cryostat Q = 4 (typical of some ~6 around the world Maryland, LSU, Rome, CERN, UWA) Fundamental resonant mode at mode resonant Fundamental bandwidth narrow Hz; ~900 capacitive Ultra-low-noise electronics and transducer (SQUID) LIGO-G000167-00-R ) L ∆ k 42 2 ( 2 sin in P = out P mirrors Dark port Dark port photodiode Beam Beam splitter

AJW, Caltech, LIGO Project LIGO AJW, Caltech, laser L , make , make Interferometric detection of GWs L ∆ Antenna pattern: (not very directional!) LIGO-G000167-00-R For fixed ability to measure as big possible! GW acts on freely GW falling masses: 43

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Terrestrial Interferometers LIGO-G000167-00-R Suspended mass Michelson- Suspended mass interferometers type surface detect on earth’s sources astrophysical distant (LIGO, network International TAMA) Virgo, GEO, and sources enable locating of polarization decomposing waves. gravitational 44 verify light speed light verify detection the sources locate decompose the Open up a new field of astrophysics! field confidence confidence of polarization waves gravitational propagation

TAMA

AIGO

Virgo

AJW, Caltech, LIGO Project LIGO AJW, Caltech, International network

GEO Simultaneously detect signal (within msec) (within signal detect Simultaneously LIGO-G000167-00-R

LIGO 45

Livingston Observatory LIGO sites

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Both sites are relatively quiet, seismically noise human low

Hanford Hanford

Observatory

(H2K and H4K) (H2K LIGO-G000167-00-R Hanford, WA (LHO) • locatedon DOE reservation •desert high semi-arid treeless, • WA Richland, from km 25 • Two IFOs: H2K andH4K Livingston, LA (LLO) • area rural in forested, located • wet climate logging, commercial • LA Baton Rouge, from 50km • One L4K IFO 47 LISA

AJW, Caltech, LIGO Project LIGO AJW, Caltech, The center of the triangle formation will be in the ecliptic plane 1 AU from the Sun and 20 degrees behind the Earth. The Laser Interferometer Space Antenna LISA (NASA/JPL, ESA) may fly in the next 10 years! LISA (NASA/JPL, ESA) LIGO-G000167-00-R Three spacecraft in orbit about the sun, with 5 million km baseline 50

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Sensitivity bandwidth rays) γ HE −> LIGO-G000167-00-R » (ULF radio » space) + (terrestrial EM waves areEM studied over waves ~20 orders of magnitude Gravitational Waves over ~10 orders of magnitude 51

AJW, Caltech, LIGO Project LIGO AJW, Caltech, , in Interferometer for GWs 10 LIGO-G000167-00-R The concept is to compare the time it takes light to travel in two orthogonal directions transverse to the gravitational waves. The gravitational wave causes the time difference to vary by stretching one arm and compressing the other. The interference pattern is measured (or the fringe is split) to one part in 10 order to obtain the required sensitivity. 52 radians -10 :

tiny For expected signal strengths, For expected signal strengths, The effect is Phase shift of ~10 The effects of gravitational waves waves The effects of gravitational phase appear as a deviation in the differences betweenorthogonal two an interferometer. paths of light The longer the light path, the larger the the path, light the The longer phase shift… as possible! path as long Make the light

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Interferometric phase difference LIGO-G000167-00-R 53 ~ 3 msec stor τ (LIGO design) design) (LIGO control to harder but More compact,

AJW, Caltech, LIGO Project LIGO AJW, Caltech, stor τ Light storage: folding the arms Simple, but requires large mirrors; large mirrors; Simple, but requires limited LIGO-G000167-00-R detectors: How to get long light light long get How to paths without making huge path! light Fold the 54 dark port signal) port (GW dark bright port bright

AJW, Caltech, LIGO Project LIGO AJW, Caltech, LIGO I configuration Power-recycled Michelson with Fabry-Perot arms: Michelson Power-recycled LIGO-G000167-00-R •Fabry-Perot optical cavities in the two arms store the light for trips round (~200) many •Michelson interferometer: change in arm lengths destroy destructive interference, light from port emerges dark light to •Normally, returns laser at bright port sends •Power recycling mirror the light back in (coherently!) to be reused 56 0 f >>

AJW, Caltech, LIGO Project LIGO AJW, Caltech, f Suspended test masses “Free” mass: “Free” mass: at pendulum LIGO-G000167-00-R •can’t simply bolt the masses to the table in typical(as ifo’s labs) in physics •“fixed” against gravity at low frequencies, but •“free” to move at frequencies above ~ 100 Hz • respond to the test To falling” GW, be “free must masses • test Earth, be supported against DC On masses must gravity field •at low vibrating like mad is lab, the and Earth, The frequencies (seismic, thermal, acoustic, electrical); • is IFO insensitive to GW’s So, low frequency • suspended on a pendulum are Test masses resting on a seismic isolation stack 57

AJW, Caltech, LIGO Project LIGO AJW, Caltech, LIGO Livingston (LLO) LIGO-G000167-00-R • Baton from 30 miles Rouge, LA (LSU) • area rural forested, logging, •Commercial wet climate • need moats (with alligators) quiet, •Seismically noise level low human 58 • DOE nuclear reservation • treeless, semi-arid high desert • from 15 miles WA Richmond, quiet, •Seismically noise level low human

AJW, Caltech, LIGO Project LIGO AJW, Caltech, LIGO Hanford (LHO) LIGO-G000167-00-R 59 LIGO beam tube beam tube LIGO construction under in January1998 welded spiral 65 ft sections girth welded in portable clean room in the field Beam light path must be high vacuum, to minimize “phase noise”

Beam Tube LIGO

AJW, Caltech, LIGO Project LIGO AJW, Caltech, LIGO-G000167-00-R 60

AJW, Caltech, LIGO Project LIGO AJW, Caltech, LIGO vacuum equipment LIGO-G000167-00-R All optical All optical must components be in high vacuum, are not so mirrors “knocked around” by gas pressure 61 BSC Chambers

AJW, Caltech, LIGO Project LIGO AJW, Caltech, LIGO Vacuum Chambers HAM Chambers LIGO-G000167-00-R 62

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Seismic isolation stacks LIGO-G000167-00-R 63 LIGO Optics

AJW, Caltech, LIGO Project LIGO AJW, Caltech,

mirrors, coating and polishing 0.5 nm 5%, except for BS) ≈ < , with feedback system f R/R /1800 in substrate λ » polished with mircoroughness < » High uniformity fused silica quartz » reflectivity as high as 99.999% » < losses 1 ppm in coating, 10 ppm » and ROC within spec. ≈(δ LIGO-G000167-00-R SUPERmirrors: Suspensions: hang 10kg optic by a single loop of wire, and hold it steady at low Mirrors are at room temperature, so they vibrate, producing phase noise 64

LIGO I noise floor Project LIGO AJW, Caltech, at the at at high high at thermal noise shot noise seismic noise lowest frequencies ½ frequencies intermediate frequencies ½ ½ LIGO-G000167-00-R Interferometry is limited Interferometry Many other noise other Many fundamental three by noise sources sources lurk underneath and must be controlled as is the instrument improved 65 -ray , X-ray, neutrino -ray γ – coincidence! •also non-GW: e.g., optical, optical, e.g., non-GW: •also • at Livingston km 4 at Hanford, 4 km • at Hanford 2 km also • 10 msec sites between time travel light Detection computation detectors among inconsistency) of (lack •coincidences •matchedtechniques filter for `known' signals suspects broad-band for •correlations behavior instrumental explicable from •deviations Multiple interferometers interferometers Multiple within LIGO •three interferometers • of 10 accuracy timing absolute microsec • bars) (interferometers, detectors AND: other

AJW, Caltech, LIGO Project LIGO AJW, Caltech, Detection Confidence !)? •seismic, acoustic, electromagnetic, acoustic, •seismic, muon weather •tilts, temperature, LIGO-G000167-00-R Environmental Monitoring signals false all possible locally to eliminate •Try possible sources many •Detectors for •Also trend (slowly-varying) information (slowly-varying) trend •Also for first time With all the noise faking With all the noise faking GW signals, be sure can we How seen the real thing we’ve ( 66 ) -21 (first coincidences) complete facilities) ( ($360M) mostly civil) mostly interferometers in vacuum) ( ( (vacuum system) (vacuum (commissioning subsystems) (initiate LIGO I Science Run) (initiate LIGO (one year integrated data(one at h ~ 10 year LIGO I schedule

AJW, Caltech, LIGO Project LIGO AJW, Caltech, LIGO-G000167-00-R 19951996 1997 NSF funding secured 1998 Construction Underway Interferometers 1999 Facility Construction 2000 Construction Interferometer 2001 Commission Construction Complete 2002 Installation Detector 2003+ Sensitivity studies run data I LIGO 2005 installation upgrade II Begin LIGO 70 Symphony » Relativity of General tests Basic »astrophysics and astronomy of field A new Space-time of the universe is (presumably!) filled vibrations:with Einstein’s Symphony soon ‘listen’ for Einstein’s Symphony LIGO will gravitationalwith permitting waves, A new window on the universe!

AJW, Caltech, LIGO Project LIGO AJW, Caltech,

Einstein’s LIGO-G000167-00-R