The LIGO Project ( Laser Interferometer Gravitational-Wave Observatory) Rick Savage – Scientist LIGO Hanford Observatory

What ? »A new kind of astronomical observatory – sensing gravitational waves Why ? »To observe the Universe through a new window – with a new sense. Like hearing in addition to seeing an orchestra. How ? »A network of ultra-sensitive, kilometer-scale laser interferometers measuring minute variations in photon propagation times. When ? »Initial phase of LIGO just completed – Oct. 20, 2010 »Advanced LIGO detectors currently under construction – plan to be operating by »Expect detections at least once per month – otherwise something fundamentally wrong with understanding of physics/astrophysics 2 Outline

Looking for Gravitational waves, not Electromagnetic waves 3 New kind of astronomical observatory

LIGO: Laser Interferometer Gravitational- wave Observatory 3002 km (L/c = 10 ms) Caltech MIT Managed and operated by Caltech & MIT with funding from NSF Goal: Direct observation of gravitational waves Open a new observational window on the Universe Livingston, LA Hanford, WA 4

5 The LIGO Scientific Collaboration

Space and time are interconnected – spacetime Massive objects cause curvature in spacetime – gravity Freely-falling massive objects follow geodesics in spacetime 6 Einstein’s theory of General Relativity Albert Einstein 1916 “Matter tells spacetime how to curve. Spacetime tells matter how to move.” J. A Wheeler

Is Einstein’s theory right ? Correctly predicts the observed precession of the perihelion of Mercury Explains the observed deflection of starlight by the Sun Gravitational red shifts Gravitational lensing Etc. Predicts that time runs slower in a gravitational field »NIST atomic clock at Boulder, Colorado at 5400 ft. elevation runs faster than other atomic clocks located closer to sea level. »Global positioning satellite system (GPS) uses atomic clocks and must correct for time dilation in the Earth’s gravitational field to achieve current accuracy 7

General relativity predicts Gravitational Waves Gravitational wave: oscillating quadrupolar strain in spacetime 8

Do Gravitational waves really exist? 9 Observation of energy loss caused by gravitational gadiation In 1974, J. Taylor and R. Hulse discovered a pulsar orbiting a companion neutron star. This “binary pulsar” provides some of the best tests of General Relativity. Theory predicts the orbital period of 8 hours should change as energy is carried away by gravitational waves. Taylor and Hulse were awarded the 1993 Nobel Prize for Physics for this work.

Potential sources of GWs Credit: AEI, CCT, LSU Coalescing Binary Systems neutron stars low mass black holes NS/BS systems Credit: Chandra X-ray Observatory Burst Sources galactic asymmetric core collapse supernovae cosmic strings ??? NASA/WMAP Science Team Cosmic GW background stochastic incoherent background Casey Reed, Penn State Continuous Sources spinning neutron stars probe crustal deformations 10

Capturing the waveform 11 Sketch: Kip Thorne Inspiral of ultra-compact stellar objects such as black holes or neutron stars in binary systems

The Challenge for LIGO Even the most energetic sources will generate oscillating length changes in LIGO of only about ~ meters i.e meters 12 Why still not detected after almost 100 years?

How Small is Meter? Wavelength of light, about 1 micron One meter, about 40 inches Human hair, about 100 microns LIGO sensitivity, meter Nuclear diameter, meter Atomic diameter, meter 13

14 Relative phase measurement via interference Constructive and destructive interference of water waves Light exhibits both particle (photon) and wave (electromagnetic) properties Lasers provide coherent light waves Michelson interferometer splits the wave into two perpendicular paths to interrogate the relative lengths of the arms. Laser

LIGO detectors Laser 4 km-long Fabry-Perot arm cavity recycling mirror test masses beam splitter Power recycled Michelson interferometer with Fabry-Perot arm cavities Power recycled Michelson interferometer with Fabry-Perot arm cavities signal 15

H1 detector sensitivity – July 10, meters S6 science run – July 2009 to October 2010

H1 detector range – July 10, Mpc = 1 million parsecs 1 parsec ~ 3 light years 20 Mpc ~ 60 million light years

How Far is 20 MegaParsecs? Speed of light is 300,000,000 meters/second One parsec = light years One year = 365 x 24 x 60 x 60 = 31,536,000 seconds LIGO trying to sense motions of meters caused by cosmic events 600,000,000,000,000,000 meters away (36 orders of magnitude in distance) 20 parsec x LY/parsec x 31,536,000 seconds/ LY x 300,000,000 meters/ sec = 617,328,552,960,000,000 meters 18

No detections - data still being analyzed Astrophysical results – upper limits »“If LIGO didn’t see it, then it can’t be bigger than …” »CRAB pulsar – “no more than 4 percent of the energy loss of the pulsar is caused by the emission of gravitational waves.” (Caltech press release) »Gamma ray burst GRB – LIGO “results give an independent way to reject hypothesis of a compact binary progenitor in M31” (Isabel Leonor for the LIGO Scientific Collaboration) 19 What have we learned so far?

What’s next? Advanced LIGO Quantum noise limited interferometer Factor of 10 increase in sensitivity Factor of 1000 increase in event rate 20

21 Laser source: 10 W to 200 W Diode-pumped YAG lasers

Vibration isolation: passive to active 22 Geophones and accelerometers on payload Active feedback control – 6 deg. of freedom Masses and damped springs

Test mass suspensions 23 Quadruple pendulum with reaction masses 40 kg test masses Single pendulum

24 Advanced LIGO ~2014 Hubble telescope WFPC2 image (NASA - JPL) Searching (listening) for gravitational waves from cosmic events located 10 times farther away (~500 million light years)

25 Movie by NSF about LIGO

Hooray for citizen scientists! The project has discovered a unusual pulsar approximately 17,000 light-years away in the constellation Vulpecula. The project works by people “donating” idle time on their home computers. This is the first deep-space discovery by and the finding is credited to Chris and Helen Colvin, from Ames, Iowa in the US, and Daniel Gebhardt of Universitat Mainz, Vulpeculacomputersspacediscovery credit: Universe Today 26