TOC

• Introduction
• Theory
• Setup
• Observation
• Conclusion

Introduction

• LIGO is ...

• Observatory to detect ...
• Gravitational Wave
• Two were built in the United States

TOC

• Introduction
• Theory
• Setup
• Observation
• Conclusion

• General Relativity
• Gravitational Wave
  • 1916

General Relativity

• Einstein's equation
• Lagrangean formulation
  • Einstein-Hilbert action
• Linearlize it

Transverse-Traceless Gauge

• Transform

• Fix gauge (transverse-traceless gauge)

Ansatz and Solutions

• Transverse-traceless gauge

• Solutions
• Impose

Gravitational Wave

Ripples in Spacetime Pond

LIGO Lab Caltech : MIT
https://www.youtube.com/watch?v=zLAmF0H-FTM

TOC

• Introduction
• Theory
• Setup
• Observation
• Conclusion

Michelson Interferometer

1. L-shaped
2. Mirrors
3. Photodetector

Challenge

• Gravitational wave is so weak
• • 10,000 times smaller than a proton

Arm length

• Longer is better
• Arm length ~ 4km
• <-> 1.3m
  • by Michelson and Morley
  • to study Aether
• But...
• Still too short to detect gravitational wave

Fabry Parot Cavities

• More mirrors
• 300 times
• 4km x 300 = 1,200km
• But...
• We need more power
  • 40W vs 750kW

Power Recycling Mirror

• Yet another mirror
• Nearly all of the laser light goes the path to the PR mirror

Initial LIGO

• Operated for 9 years (2002 - 2010)
• Never detected gravitational waves

Advanced LIGO

• Built taking 7 years
  • 2008 - 2015

• Better mirrors
• Better suspension
• Better seismic isolation
• Aimed 10 times more sensitive than the initial LIGO

Advanced LIGO

• Built taking 7 years
  • 2008 - 2015
• Better mirrors
• Better suspension
• Better seismic isolation
• 4 times more sensitive than the initial LIGO

TOC

• Introduction
• Theory
• Setup
• Observation
• Conclusion

First Observation - GW150914

Made on 14 September 2015, Announced on 11 February 2016.
Two black holes colliding and merging into one nearly 1.3 BILLION light years away.

Another detection - GW170817

First LIGO/Virgo detection of a binary neutron star merger (GW170817)
https://www.youtube.com/watch?v=_SQbaILipjY
© Alex Nitz/Max Planck Institute for Gravitational Physics/LIGO

Time-frequency representation (spectrogram) of the LIGO-Hanford and LIGO-Livingston data. Your ears are the two LIGO detectors. The observed data is revealed in real time, accompanied by the audio presentation of the plotted data.

TOC

• Introduction
• Theory
• Setup
• Observation
• Conclusion

Conclusion

Laser Interferometer is ...

Conclusion

Laser Interferometer is good to

Detect a Gravitational Wave

References

• LIGO Caltech
  • https://www.ligo.caltech.edu/page/ligos-ifo
• LIGO (Wikipedia)
  • https://en.wikipedia.org/wiki/LIGO
• First observation of gravitational waves (Wikipedia)
  • https://en.wikipedia.org/wiki/First_observation_of_gravitational_waves