LIGO: The Search for the Gravitational Wave Sky
• Science • LIGO status • UO in LIGO
R Frey Oct 2008 1 General Relativity
• Gravit y as a “fi c titious f orce” Gravity can be “removed” in a special ref. frame -- free fall • Einstein took this as a clue that gravity is really caused by the structure of spacetime • Postulates of General Relativity (Einstein ca. 1915): Equivalence of inertial and gravitational mass There is no physics experiment which can distinguish between a gravitational field and an accelerating reference frame • An elevator at rest in earth’s gravity (g=9.8 m/s2) • An elevator accelerating upward with a= 9. 8 m/s2 • What this means extends special relativity to non-zero acceleration GitGravity re-dibddescribed as curva ture o f space time • A test particle (or light) in free fall follows a “straight” geodesic
R Frey Oct 2008 2 General Relativity (contd)
SdiiSome predictions: Gravity influences both mass and energy • e.g. bending of light in regions with gravitational field • 1919 Eddington; Gravitational lensing: Einstein Cross Many small deviations from Newtonian gravity in “weak” fields • Gravitational “redshift” (e.g. clocks on satellites are faster) • Perihelion advance of mercury • Global Positioning System would not work without GR corrections “Strong” field effects 2 • Black holes; Rs = 2GM/c Spacetime structure of universe – evolution of spacetime from Big Bang • the “bi g s tre tc h” And gravitational radiation (gravitational waves)
R Frey Oct 2008 3 GWs in GR
R Frey Oct 2008 4 The 4 Forces of Nature
• Gravity is by far the weakest force • Gravityygy and gravity waves ⇔ Electromagggnetism and Light
• Gravitational waves have not yet been observed ! • No quantum theory of gravity (graviton ⇔ photon) … yet
R Frey Oct 2008 5 Evidence (indirect) for Gravitational Waves
PSR 1913+16 Binary n-star system
T60T=60 ms • •
T ~ 8 hr Pulsar period observed over 25 years – Taylor and Hulse
R Frey Oct 2008 6 GW Science
Goals: Establish GW detection Test GR: weak and strong fields Use GW as an astrophysical tool
GW revolution like radio astronomy?
R Frey Oct 2008 7 Laser Interferometer Gravitational-wave Observatory
4 km & 2 km WA
• Ground breaking 1995 • 1s t in terf eromet er l ock 2000 • LIGO Scientific LA collaboration: 45 institutions, world-wide 4k4 km • GEO and Virgo detectors in Europe
R Frey Oct 2008 8 GW Interferometer Principle
GW strain: h = δL/ L
R Frey Oct 2008 9 Required GW Sensitivity
• GW emi ssi on requ ires time vary ing qua drupo le momen t o f mass distribution • Strain estimate (h = δL / L) :
R Frey Oct 2008 10 Interferometer parameters
• Long baseline 4 km ( h = δL/ L ) - For h ≈10-21, L ≈ 1 km, then δL ≈ 10-18 m ⇒δΦ≈ 10-9 rad required phase sensitivity • Fabry-Perot Cavity storage time ∼1 ms (∼100 bounces) • High laser power (λ = 1 μm) Power recycling (x30) Cavities: Few watts in; few kW in arms
R Frey Oct 2008 11 What Limits Sensitivity of the Interferometers?
• Seismic noise & vibration limit at low frequencies • Thermal noise of suspensidttions and test masses • Quantum nature of light (Shot Noise) limits at high frequencies Approaching quantum measurement limits (for a 10 kg mass!) Squeezed light experiment in 2009 • Limitations of facilities much lower
R Frey Oct 2008 12 S5 Science Run: LIGO at Design Sensitivity
R Frey Oct 2008 13 Inspiral sensitivity in S5: NS-NS Binary merger sensitivity in S5 BH-BH
R Frey Oct 2008 14 Astrophysical Signal Types
• Compact binary inspiral: “chirps” NS-NS, BH -BH waveforms are well described search technique: matched templates
• Supernovae / GRBs: “bursts”bursts SN 1987 A “unmodelled” search triggered searches
• Pulsars in our galaxy: “periodic” observe known neutron stars (frequency, doppler shift) all sky search (computing challenge) Low-mass X-ray binaries
• Cosmological “stochastic background” Tests of inflation? GWs neutrinos photons R Frey Oct 2008 now 15 Coalescing Compact Binaries
NS-NS, BH-BH, (BH-NS) binary systems
Matched filter Template-less Matched filter
R Frey Oct 2008 16 Gravitational Radiation and Gamma-ray Bursts
BATSE Long-duration GRBs • Stronger afterglows → z • SNe or “hypernovae” • mean z ≈ 2.5 GSFC
Short-duration GRBs GRB030329 • Until 2005, no measured z’s → enter Swift HETE-2 • Now: a few z’s → “compact binary mergers” • mergers are efficient Oct 6, 2 GW radiators • much smaller z’s
0 (mean 04)0.4)
05 ≈
Over 200 GRBs in S5 R Frey Oct 2008 17 Non-detection of GW (so far) but making relevant astrophysical observations
Observation I -- ruling out a GRB in Andromeda (ApJ 2008)
• GRB 070201 – a short-duration gamma-ray burst with position consistent with M31 (Andromeda) • Such a nearby GRB would have easily been observed by LIGO
• Ruled out at ~99% CL
• Like ly sources: a GRB be hin d or an SGR in M31
R Frey Oct 2008 18 observations (contd)
Observation II – beating the Crab pulsar spin-down limit (ApJ Lett)
• Crab pppulsar is spin rate is gradually slowing down • The energy loss goes into EM and GW emission • All into GW?
• No. In fact, LIGO limit implies GW emission accounts for ≤ 4% of age mm total spin -down power odel handra i handra MM CC
R Frey Oct 2008 19 observations (contd)
Observation III – beating the BBN limit for a cosmic GW background from the early universe (soon…)
R Frey Oct 2008 20 UO people in LIGO
• Faculty and senior scientist Jim Brau Ray Frey David Strom Robert Schofield, Sr. Research Scientist • half-time on site at Hanford • Postdocs Isabel Leonor, leads the GRB analysis effort • Graduate students Emelie Harstad Masahiro Ito, PhD 2006, supernova search Rauha Rahkola, PhD 2006, GRB search
R Frey Oct 2008 21 What does UO do in LIGO?
• Improve the detectors • Determine couplings of environment on detectors seismic, magnetic fields, acoustic, cosmic rays • Analyze data for gravitational waves! Aitiith“tlltid”tAssociation with “externally triggered” events: gamma-ray bursts, supernovae, gamma-ray repeaters, neutrinos
R Frey Oct 2008 22 The Future: Enhanced and Advanced LIGO
S5 Run S6 S7 2006 2007 2008 20092010 2011 2012 2013 2014 LIGO enhanced LIGO Advanced LIGO Advanced LIGO is build hardware installation science funded, starting 2008 Enhanced LIGO (S6) • readout noise; laser power • ×2 better sensitivity •commiss ion AdLIGO rea dou t with real IFOs • reduce AdLIGO startup time
Advanced LIGO • Major upgrades: optics, lilasers, suspensions, ... • ×10 better sensitivity
R Frey Oct 2008 23 WW GW network
R Frey Oct 2008 24 R Frey Oct 2008 25