1. The Laser Interferometer Gravitational-wave Observatory
and the search for the elusive wave
Nergis Mavalvala
Visiting committee, October 2008

2. Gravitational waves (GWs)
Prediction of Einstein’s General Relativity (1916)
Indirect detection led to Nobel prize in 1993
Ripples of the space-time fabric
GWs stretch and squeeze the space transverse to direction of propagation
Emitted by accelerating massive objects
Cosmic explosions
Compact stars orbiting each other
Stars gobbling up stars
“Mountains” on stellar crusts 

3. GW detector at a glance Mirrors hang as pendulums Quasi-free particles
Respond to passing GW
4 km
20 kW
Optical cavities
Mirrors facing each other
Builds up light power
Lots of laser power P
Signal  P
Noise 
10 W

4. Global network of detectors
GEO
VIRGO
LIGO
TAMA
AIGO
LIGO
Detection confidence
Source polarization
Sky location
LISA

6. Initial LIGO Sensitivity

7. Gravitational-wave searches

8. Science Run 5 (2005 – 2007) S5

9. The mystery of GAMMA RAY BURSTs
Is it a supernova explosion or is it a compact binary merger?

10. GRB070201
Intense GRB located in an error box that includes the spiral arms of the nearby Andromeda galaxy (M31)
About 2.5 million l.y. away
Detected by Konus-Wind, Integral, Swift and Messenger
LIGO detectors were on the air at the time

11. What did LIGO find? LIGO did not detect a signal
DM31
25%
50%
75%
90%
LIGO did not detect a signal
Consequence: we can say with >99% confidence that GRB was NOT caused by a binary star merger in M31
35 observational papers since 2003
Astrophys. J 681 (2008) 1419

12. Coming soon… to an interferometer near you
Enhanced LIGO Advanced LIGO

13. Ultimate limits ? Seismic gravity gradient
When ambient seismic waves pass near and under an interferometric gravitational-wave detector, they induce density perturbations in the Earth, which in turn produce fluctuating gravitational forces on the interferometer’s test masses.
Human gravity gradient
The beginning and end of weight transfer from one foot to the other during walking produces the strongest human-made gravity-gradient noise in interferometric gravitational-wave detectors (e.g. LIGO). The beginning and end of weight transfer entail sharp changes (time scale τ∼20 msec) in the horizontal jerk (first time derivative of acceleration) of a person’s center of mass.

14. Improved sensitivity
Initial LIGO
Enhanced LIGO
Advanced LIGO

15. Improved reach Initial LIGO Enhanced LIGO Advanced LIGO
EnLIGO
Enhanced LIGO
Initial LIGO can “see” ~ 1000 galaxies
Enhanced LIGO (2009) ~ galaxies
Advanced LIGO (2015) ~ million galaxies
Important for catching distant and/or rare events
Advanced LIGO

16. The LIGO Group at MIT

17. LIGO Laboratory Organization

18. LIGO Laboratory Joint Caltech and MIT project
Initial LIGO was ~ $400M to construct and ~$30M/yr to operate
Advanced LIGO ~$200M
Largest project at the NSF
Laboratory personnel
Caltech ~ 100 (6 faculty, 30 senior research staff)
MIT ~ 35 (4 faculty, 5 senior research staff)
Hanford Observatory ~ 30
Livingston Observatory ~ 30
LIGO directorate and business office at Caltech
Much leadership and intellectual influence at MIT

19. MIT LIGO group Faculty Senior research staff
Founding father, problem solver at large
Lead on searches for burst (transient) sources, computing
Leader of the quantum measurement group
GR astrophysics and GW sources
Faculty
Rai Weiss
Erik Katsavounidis
Nergis Mavalvala
(Scott Hughes)
Senior research staff
David Shoemaker
Peter Fritschel
Mike Zucker
Gregg Harry
Rich Mittleman
6 Ph.D. and 4 Masters since 2003
Leader of AdLIGO, Director of MIT LIGO Lab
Systems scientist, leader of major subsystem for AdLIGO, initial proposer and designer of EnLIGO
Former director of LIGO Livingston Observatory, presently co-leading Enhanced LIGO implementation
Lead scientist on optical coatings for Advanced LIGO
Head of the prototyping lab at MIT, lead on AdLIGO mechanical isolation systems

20. Closing remarks

21. When the elusive wave is captured…
Tests of general relativity
Waves  direct evidence for time-dependent metric
Black hole signatures  test of strong field gravity
Polarization of the waves  spin of graviton
Propagation velocity  mass of graviton
Astrophysics
Predicted and unexpected sources
Inner dynamics of processes hidden from EM astronomy
Dynamics of neutron stars  large scale nuclear matter
The earliest moments of the Big Bang  Planck epoch
Precision measurement below the quantum limit

22. In closing...
Astrophysical searches from early science data runs completed
The most sensitive search yet (S5) completed with 1 year of data at initial LIGO sensitivity
Joint searches with partner observatories
Enhanced LIGO implementation that should give 2 to 3x improvement in sensitivity underway
Advanced LIGO construction begun (funded as of FY2008)
Promising prospects for direct GW detection in coming years

23. The End