LIGO Detection of Gravitational Waves. Dr. Stephen Ng

LIGO Detection of Gravitational Waves Dr. Stephen Ng

Gravitational Waves Predicted by Einstein s general relativity in 1916 Indirect confirmation with binary pulsar PSR B1913+16 (1993 Nobel prize in physics) Direct detection? 2/24/2016 LIGO detection of gravitational waves Stephen Ng

Astrophysical sources Massive objects Fast-moving Periodic signals 2/24/2016 LIGO detection of gravitational waves Stephen Ng

Astrophysical sources Massive objects Fast-moving Periodic signals Blackhole-blackhole merger Blackhole-neutron star merger Neuton star-neutron star merger 2/24/2016 LIGO detection of gravitational waves Stephen Ng

https://www.ligo.caltech.edu/video/ligo20160211v1

Detection Technique Michelson interferometer 2/24/2016 LIGO detection of gravitational waves Stephen Ng

https://www.ligo.caltech.edu/video/ligo20160211v6

2/24/2016 LIGO detection of gravitational waves Stephen Ng

Laser Interferometer Gravitational-Wave Observatory (LIGO) Hanford, Washington Livingston, Louisiana Two orthogonal 4km arms 2/24/2016 LIGO detection of gravitational waves Stephen Ng

Hanford

Livingston

2/24/2016 Stephen Ng

40kg silica test mass 2/24/2016

2/24/2016 LIGO detection of gravitational waves Stephen Ng

Sensitivity 60Hz power grid 500Hz suspension fibers >150Hz shot noise Thermal noise Rayleigh scattering 2/24/2016

1011 authors!

GW150914 2015 Sep 14, 09:50:45 UTC Advanced LIGO upgrade (Virgo, GEO600 not working) Detected at both sites, 6.9 +0.5 0.4 ms delay 2/24/2016

GW150914 2015 Sep 14, 09:50:45 UTC Advanced LIGO upgrade (Virgo, GEO600 not working) Detected at both sites, 6.9 +0.5 0.4 ms delay Increased from 35Hz to 150Hz in 0.2s 2/24/2016

2/24/2016

https://www.ligo.caltech.edu/video/ligo20160211v2

GW150914 2015 Sep 14, 09:50:45 UTC Advanced LIGO upgrade (Virgo, GEO600 not working) Detected at both sites, 6.9 +0.5 0.4 ms delay Increased from 35Hz to 150Hz in 0.2s Peak strength 1.0 10 21 - Exercise: displacement between test masses? 2/24/2016

https://www.ligo.caltech.edu/video/ligo20160211v7

Is It Real? 2/24/2016 LIGO detection of gravitational waves Stephen Ng

Detector Validation Detectors steady for several hours - Not instrumental artifacts Environmental sensors show no disturbances - Seismometers, accelerometers, microphones, magnetometers, radio receivers, weather sensors, ac-power monitors, cosmic-ray detector, 2/24/2016 LIGO detection of gravitational waves Stephen Ng

Searching for Signals Generic search False alarm rate: 1 in 8,400yr False alarm prob.: 5 10 6 = 4.4 detection Binary coalescence search 250,000 post-newtonian templates 1-99M, spin a cj GM 2 0.99 False alarm rate: 1 in 203,000yr False alarm prob.: 5 10 6 = 5.1 detection 2/24/2016 LIGO detection of gravitational waves Stephen Ng

Searching for Signals Generic search Binary coalescence search

2/24/2016

Searching for Signals Generic search Binary coalescence search

Confirmed! 2/24/2016 LIGO detection of gravitational waves Stephen Ng

What source? Chirp mass M m 3/5 1m 2 = c3 m 1 +m 1/5 2 G 5 96 π 8/3 f 11/3 ሶ f 3/5 30M Exercise 1: Total Mass M = m 1 + m 2 70M (hint: let X = m 1 + m 2 and Y = m 1 m 2 ) Exercise 2: If m 1 = 1.4M, m 2 3000M 75Hz => 350km apart Black hole-black hole merger 2/24/2016 LIGO detection of gravitational waves Stephen Ng

2/24/2016 Stephen Ng

https://www.ligo.caltech.edu/video/ligo20160211v10

Black Hole Parameters Full GR numerical simulation of binary black hole mergers: Primary black hole mass Secondary black hole mass 36 +5 4 M 29 +4 4 M Final black hole mass 62 4 M Final black hole spin +0.05 0.67 0.07 Energy radiated in gravitational waves 3.0 +0.5 0.5 M c 2 = 5.4 +0.9 0.9 10 54 erg Peak luminosity 200 +30 20 M c 2 /s = 3.6 +0.5 0.4 10 56 erg/s Redshift +0.03 0.09 0.04 2/24/2016 LIGO detection of gravitational waves Stephen Ng

Where? 600 deg 2 No EM, no 2/24/2016

ArXiv:1602.03920 600deg 2 200deg 2

Physical Implications Graviton mass < 1.2 10 22 ev/c 2 Heavy ( 25M ) stellar mass black holes exist Weak stellar winds => Low metallicity ( 1/2 solar values) Binary black hole merger rate 2 400Gpc 3 yr 1 Low metallicity, low redshift => Black hole binary formation in: low-mass galaxy in local universe with prompt merger, or high redshift, delay merger several Gyr 2/24/2016 LIGO detection of gravitational waves Stephen Ng

What Next? More observatories Advanced LIGO

What Next? More observatories Advanced LIGO Laser Interferometer Space Antenna (LISA) Pulsar timing array 2/24/2016 LIGO detection of gravitational waves

2/24/2016

A New Window to the Universe This is not an end, but just the beginning Multi-messenger astronomy beyond EM waves - Gravitational waves ( listen to the Universe) - Neutrino - Cosmic rays 2/24/2016 LIGO detection of gravitational waves Stephen Ng

Conclusions Gravitational waves finally detected, 100yr after proposed A new window to the Universe To testing simple principles - Precise measurements - Careful design of experiments - Advanced technology - Careful checking => Discovery 2/24/2016 LIGO detection of gravitational waves Stephen Ng

2/24/2016

References https://www.ligo.caltech.edu/gallery https://journals.aps.org/prl/abstract/10.1103/physrevlett.116.06110 2#fulltext http://www.nature.com/news/einstein-s-gravitational-waves-foundat-last-1.19361 http://rhcole.com/apps/gwplotter/ 2/24/2016 LIGO detection of gravitational waves Stephen Ng