LIGO - University of Oregon
advertisement
LIGO: The Search for the Gravitational Wave Skyy • Science • LIGO status • UO in LIGO R Frey Oct 2008 1 General Relativity • • • Gravity G it as a “fictitious “fi titi force” f ” 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 9.8 8 m/s2 • What this means extends special relativity to non-zero acceleration Gravity G it re-described d ib d as curvature t off spacetime ti • A test particle (or light) in free fall follows a “straight” geodesic R Frey Oct 2008 2 General Relativity (contd) S Some predictions di i : 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” redshift (e.g. clocks on satellites are faster) • Perihelion advance of mercury • Global Positioning System would not work without GR corrections “Strong” Strong field effects • Black holes; Rs = 2GM/c2 Spacetime structure of universe – evolution of spacetime from Big Bang • the th “big “bi stretch” t t 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 • Gravity y and gravity g y waves ⇔ Electromagnetism g and Light g • 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 T 60 ms T=60 • • Pulsar period observed over 25 years T ~ 8 hr – Taylor and Hulse R Frey Oct 2008 6 GW Science Goals: Establish GW detection Test GR: weak and strong g fields Use GW as an astrophysical tool GW revolution like radio astronomy? R Frey Oct 2008 7 Laser Interferometer Gravitational-wave Observatoryy 4 km & 2 km WA • Ground breaking 1995 • 1st 1 t iinterferometer t f t lock l k 2000 • LIGO Scientific collaboration: 45 institutions, world-wide ld id LA 4 kkm • 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 emission i i requires i titime varying i quadrupole d l momentt off mass distribution • Strain estimate (h = δL / L)) : R Frey Oct 2008 10 Interferometer parameters • Long g 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 suspensions i and d ttestt masses Quantum nature of light g (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 BH-BH Binary merger sensitivity in S5 R Frey Oct 2008 14 Astrophysical Signal Types • Compact binary inspiral: “chirps” NS NS-NS NS, BH BH-BH BH waveforms are well described search technique: matched templates • Supernovae / GRBs: “bursts” bursts “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? SN 1987 A GWs neutrinos photons R Frey Oct 2008 now 15 Coalescing Compact Binaries NS-NS, BH-BH, (BH-NS) binary systems Matched filter Template-less R Frey Oct 2008 Matched filter 16 Gravitational Radiation and Gamma-ray Bursts BATSE Long duration GRBs Long-duration • Stronger afterglows → z • SNe or “hypernovae” hypernovae • mean z ≈ 2.5 GSFC Short-duration GRBs • Until 2005,, no measured z’s → enter Swift • Now: a few z’s → “compact binary mergers” GRB030329 HETE-2 Oct 6, 20 005 • mergers are efficient GW radiators • much smaller z’s (mean ≈ 0.4) 0 4) R Frey Oct 2008 Over 200 GRBs in S5 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 • Lik Likely l sources: a GRB b behind hi d or an SGR in M31 R Frey Oct 2008 18 observations (contd) Observation II – beating the Crab pulsar spin spin-down down limit (ApJ Lett) • No. In fact, LIGO limit implies GW emission accounts for ≤ 4% of total spin-down spin down power Model M Chandra im C mage • Crab p pulsar is spin p rate is gradually slowing down • The energy loss goes into EM and GW emission • All into GW? 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 • Facultyy and senior scientist Jim Brau Ray Frey David Strom Robert Schofield, Sr. Research Scientist • half half-time time on site at Hanford • Postdocs Isabel Leonor, leads the GRB analysis effort • Graduate students Emelie Harstad Masahiro Ito Ito, PhD 2006 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! Association A i ti with ith ““externally t ll ttriggered” i d” events: t gamma-ray bursts, supernovae, gamma-ray repeaters, neutrinos R Frey Oct 2008 22 The Future: Enhanced and Advanced LIGO S5 Run 2006 S7 S6 2007 LIGO Advanced LIGO is funded, starting 2008 2008 2009 2010 2011 2012 2013 2014 enhanced LIGO Advanced LIGO build hardware installation science Enhanced LIGO (S6) • readout noise; laser power • ×2 better sensitivity • commission i i AdLIGO readout d t with real IFOs • reduce AdLIGO startup time Advanced LIGO • Major upgrades: optics, l lasers, suspensions, i ... • ×10 better sensitivity R Frey Oct 2008 23 WW GW network R Frey Oct 2008 24 R Frey Oct 2008 25
