LIGO: The Search for the Gravitational Wave Skyy

• Science

• LIGO status• LIGO status

• UO in LIGO

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General Relativity

G it “fi titi f ”• Gravity as a “fictitious force”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 spacetimespacetime

• Postulates of General Relativity (Einstein ca. 1915):Equivalence of inertial and gravitational massThere 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• An elevator accelerating upward with a= 9.8 m/s2

• What this meansextends special relativity to non-zero accelerationG it d ib d t f tiGravity re-described as curvature of spacetime

• A test particle (or light) in free fall follows a “straight” geodesic

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General Relativity (contd)

S di iSome 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)Gravitational redshift (e.g. clocks on satellites are faster) • Perihelion advance of mercury• Global Positioning System would not work without GR corrections

“Strong” field effectsStrong field effects• Black holes; Rs = 2GM/c2

Spacetime structure of universe – evolution of spacetime from Big Bangth “bi t t h”• the “big stretch”

And gravitational radiation (gravitational waves)

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GWs in GR

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The 4 Forces of Nature

• Gravity is by far the weakest force

• Gravity and gravity waves ⇔ Electromagnetism and Lighty g y g g

• Gravitational waves have not yet been observed !• No quantum theory of gravity (graviton ⇔ photon) yet

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• No quantum theory of gravity (graviton ⇔ photon) … yet

Evidence (indirect) for Gravitational Waves

T 60

PSR 1913+16 Binary n-star system

•T=60 ms

••T ~ 8 hr

Pulsar period observed over 25 years

– Taylor and Hulse

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GW Science

Goals:Establish GW detection Test GR: weak and strong fieldsgUse GW as an astrophysical tool

GW revolution like radio astronomy?

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Laser Interferometer Gravitational-wave Observatoryy

WA4 km & 2 km

• Ground breaking 1995

1 t i t f t l k 2000

LA4 k

• 1st interferometer lock 2000

• LIGO Scientific collaboration: 45 institutions,

ld id 4 kmworld-wide

• GEO and Virgo detectors in Europe

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GW Interferometer Principle

GW strain: h = δL/ L

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Required GW Sensitivity

GW i i i ti i d l t f• GW emission requires time varying quadrupole moment of mass distribution

• Strain estimate (h = δL / L) :( )

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Interferometer parameters

• Long baseline 4 km ( h = δL/ L ) - For h ≈10-21, L ≈ 1 km, then δL ≈ 10-18 mg ( )⇒ 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 armsCavities: Few watts in; few kW in arms

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What Limits Sensitivityof the Interferometers?of the Interferometers?

• Seismic noise & vibrationSeismic noise & vibration limit at low frequencies

• Thermal noise of i d t tsuspensions and test

masses• Quantum nature of light g

(Shot Noise) limits at high frequencies

Approaching quantumApproaching quantum measurement limits (for a 10 kg mass!)Squeezed light experiment in 2009

• Limitations of facilities much

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Limitations of facilities much lower

S5 Science Run: LIGO at Design Sensitivity

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Binary merger sensitivity in S5

Inspiral sensitivity in S5:

NS-NSBinary merger sensitivity in S5BH-BH

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Astrophysical Signal Types

• Compact binary inspiral: “chirps”NS-NS BH-BH waveforms are well describedNS NS, BH BH waveforms are well describedsearch technique: matched templates

• Supernovae / GRBs: “bursts” SN 1987 A• Supernovae / GRBs: bursts“unmodelled” searchtriggered searches

SN 1987 A

• 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

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GWsneutrinos

photonsnow

Coalescing Compact Binaries

NS-NS, BH-BH, (BH-NS) binary systems

Matched filter Template-less Matched filter

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Gravitational Radiation and Gamma-ray Burstsand Gamma-ray Bursts

BATSE Long duration GRBsBATSE Long-duration GRBs

• Stronger afterglows → z

• SNe or “hypernovae”SNe or hypernovae

• mean z ≈ 2.5GSFC

GRB030329Short-duration GRBs

• Until 2005, no measured z’s → enter SwiftHETE-2

,

• Now: a few z’s → “compact binary mergers”

• mergers are efficient Oct 6, 20

GW radiators

• much smaller z’s (mean ≈ 0 4)

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005

(mean ≈ 0.4)

Over 200 GRBs in S5

Non-detection of GW (so far) but making relevant astrophysical observationsrelevant astrophysical observations

Observation I -- ruling out a GRB in Andromeda (ApJ 2008)Andromeda (ApJ 2008)

• GRB 070201 – a short-duration gamma-ray burst with position consistent with M31 (Andromeda)

• Such a nearby GRB would have• Such a nearby GRB would have easily been observed by LIGO

• Ruled out at ~99% CL

Lik l GRB b hi d• Likely sources: a GRB behind or an SGR in M31

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observations (contd)

Observation II – beating the Crab pulsar spin down limit (ApJ Lett)pulsar spin-down limit (ApJ Lett)

• Crab pulsar is spin rate is p pgradually slowing down

• The energy loss goes into EM and GW emissionGW emission

• All into GW?

• No. In fact, LIGO limit implies GW emission accounts for ≤ 4% of total spin down powerm

age

total spin-down power

Cha

ndra

im

Mod

el

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C M

observations (contd)

Observation III – beating the BBN limit for a cosmic GW backgroundlimit for a cosmic GW background from the early universe (soon…)

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UO people in LIGO

• Faculty and senior scientistyJim BrauRay FreyDavid StromRobert Schofield, Sr. Research Scientist

• half-time on site at Hanfordhalf time on site at Hanford• Postdocs

Isabel Leonor, leads the GRB analysis effort• Graduate students

Emelie HarstadMasahiro Ito PhD 2006 supernova searchMasahiro Ito, PhD 2006, supernova searchRauha Rahkola, PhD 2006, GRB search

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What does UO do in LIGO?

• Improve the detectors• Determine couplings of environment on detectorsDetermine couplings of environment on detectors

seismic, magnetic fields, acoustic, cosmic rays• Analyze data for gravitational waves!

A i ti ith “ t ll t i d” tAssociation with “externally triggered” events: gamma-ray bursts, supernovae, gamma-ray repeaters, neutrinos

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The Future: Enhanced and Advanced LIGO

S5 Run S6 S72006 2007 2008 2009 20112010 2012 2013 2014

enhanced LIGOAdvanced LIGO

LIGO

Enhanced LIGO (S6)

Advanced LIGObuild hardware installation scienceAdvanced LIGO is

funded, starting 2008

Enhanced LIGO (S6)• readout noise; laser power• ×2 better sensitivity

i i AdLIGO d t• commission AdLIGO readout with real IFOs

• reduce AdLIGO startup time

Advanced LIGO• Major upgrades: optics,

l i

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lasers, suspensions, ...• ×10 better sensitivity

WW GW network

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