Gravitational Wave Detectors:
Back to the Future
Raffaele Flaminio
National Astronomical Observatory of Japan

University of Tokyo, March 12th, 20171

Summary

Short introduction to gravitational waves (GW) GW sources and amplitudes
 Laser interferometer gravitational wave detectors

The LIGO-Virgo experience Initial detectors
 Advanced detectorsPerspectives in the US and in Europe Advanced LIGO+, Voyager, Cosmic Explorer
 Einstein Telescope LISA

University of Tokyo, March 12th, 20172

Gravitational waves
Many of the most energetic phenomena in the Universe are
expected to be source of gravitational waves

Merger of compact stars
 Black holes and neutron stars



Massive star explosions
 Supernovae, Gamma ray bursts



The Big Bang
 Universe is transparent to GWTheir detection is shedding light on the Dark Universe
University of Tokyo, March 12th, 20173

Gravitational waves amplitude


Gravitational wave amplitudes on Earth are tinyTwo examples: Coalescence of two stellar mass black holes at a distance of 1 Gpc
 Explosion of Supernovae in the Virgo cluster (converting 10-2 solar mass intoGW) Expected GW amplitude at the Earth dL/L ~ 10-21

University of Tokyo, March 12th, 2017

4

GW detection with laser interferometersIn the 80’s it became clear that the detection of GW amplitudesof the order of 10-21 was possible
 km-scale laser interferometers were needed

University of Tokyo, March 12th, 20175

Ronald W. P. Drever

The inventor of nowadays interferometer optical configurations
 Fabry Perot cavities in the arms
 Power recycling technique Signal recycling technique Laser frequency stabilization technique» “Pound-Drever-Hall technique”

Advanced LIGO
optical configuration

University of Tokyo, March 12th, 20176

End of the 80’s
Proposals to build km-scale laserinterferometers Required investment ~ 100 M$ / interferometer + salaries



LIGO (US) Two interferometers, 4km long
 Approved in 1990, construction started in 1994



Virgo (France-Italy)
 One interferometer, 3km long
 Approved in 1993, construction started in 1996

GEO (Germany-UK)
 One interferometer, 3km long
 Not approved (effect of German reunification)
 GEO600 (600m long) funded by Lower Saxony

University of Tokyo, March 12th, 20177

More than a supreme laser interferometer

Many challenges: vibration isolation, lasers, coatings, vacuum,electronics, signal processing, …
 An additional challenge: have all these experts working together in the same
project!

University of Tokyo, March 12th, 20178

Initial LIGO/Advanced LIGO timeline
1986
1990
1992
1994
1997
2002
2004
2006
2007
2008
2014

Physics Decadal Survey endorses LIGONational Science Board (NSB) approves LIGO construction
proposal
NSF selects LIGO sites in Washington and Louisiana states.
Site construction begins
The LIGO Scientific Collaboration (LSC) is establishedFirst coincident operation of initial LIGO interferometers andGEO600
NSB approves Advanced LIGO
LIGO design sensitivity achieved.
Joint data analysis agreement ratified between LIGO and Virgo.
Joint observations with LIGO and Virgo starts.
Construction of Advanced LIGO components begins
Advanced LIGO installation complete

September 14, 2015 First GW detection!
University of Tokyo, March 12th, 20179

Initial Virgo/Advanced Virgo timeline
1989 Virgo proposal
1993 Virgo approved by France and Italy
1996 Site construction begins
2003 Installation completed
2007 Joint data analysis agreement
ratified between LIGO and Virgo. Jointobservations with LIGO and Virgo starts.
2009 Construction of Advanced Virgostarts
2016 Advanced Virgo installation
completed

University of Tokyo, March 12th, 201710

LIGO/Virgo projects and collaboration

Large projects
 > 100 M$
 Several 100’s scientists (LIGO+Virgo = 1000 people)
 Project management culture required» Already common in large astronomy projects, had just entered the field of particle
physics in the 90’s

 Unite scientists from different fields» astrophysics, particle physics, optics, general relativity, signal processing, etc.

LIGO-Virgo collaboration model Independent projects» Independent detector funding and construction

 Joint operation planning Full data sharing
 Joint data analysis groups and internal review
 Joint publications» Common publication policy» Typical of large collaborations

University of Tokyo, March 12th, 201711

A world-wide network of detectors
Adv LIGO, USA,Hanford, 4 km

Advanced Virgo

Adv LIGO, US,Livingston, 4 km

University of Tokyo, March 12th, 2017

GEO-HF, Germany,Hannover, 600 m

Adv Virgo, Italy,Cascina, 3 km

INDIGOLIGO - India(planned tostart in 2024)

KAGRA, Japan
Kamioka, 3 km
(planned for 2019)12Source localization
LIGO and INDIGO consortium agreed to install the 3rd
Advanced LIGO detector in India
 LIGO-India Larger baseline Better source localization

University of Tokyo, March 12th, 201713

Observing scenario

Under discussion

University of Tokyo, March 12th, 201714

Observing scenario

Under discussion

University of Tokyo, March 12th, 201715

Perspectives
IMPORTANT: GW detectors sense amplitude=> a factor of 2 improvement in sensitivity increase rate of events by 8

University of Tokyo, March 12th, 201716
Credit: R. Powell

Perspective in the US: A+
Advanced Virgo + Cost: “a small fraction of Advanced LIGO”
 Improve sensitivity by 1.7 and so event rates by 5A+ key parameters:12dB injectedsqueezing
15% readout loss
100 m filter cavity
20 ppm RT FC loss
CTN half of aLIGO

University of Tokyo, March 12th, 201717

Perspectives in the USUnder discussion

University of Tokyo, March 12th, 201718

Perspectives in the US: Cosmic ExplorerA new facility: 40 km long?

University of Tokyo, March 12th, 201719

Perspectives in Europe:
Einstein TelescopeProposal for a new European infrastructure devoted to GW
astronomy Design study financed by the EU. Released in 2011
 Goal: x10 better sensitivity compared to advanced detectors



Keywords:
 Underground 10 km triangle
 Cryogenic

University of Tokyo, March 12th, 201720

Perspectives in Europe:
Einstein Telescope
Several countries involved in Europe (DE, FR, IT, GB, NL, …)
 Important to get on the ESFRI Roadmap European Strategy Forum for Research Infrastructures
Possible timeline

University of Tokyo, March 12th, 201721

Laser Interferometer Space Antenna

Laser Interferometer Space Antenna: LISA
 3 Michelson interferometers» L = 2.5 million km

 3 S/C in heliocentric orbit 20 degrees behind the earth Plane inclined by 60 degrees
Sensitive to low frequencies
 10-3 – 10-1 Hz

Complementary toground-based detectors



Selected as L3 mission by ESA Launch planned in 2034
 Possible to anticipate after the LISA Pathfinder results
 Contribution from NASA under discussion
University of Tokyo, March 12th, 201722

Laser Interferometer Space Antenna

Massive black hole binary
inspiral and merger
 Dynamical behavior of space-time Growth of massive black holes
 Absolute distances

Ultra compact binaries
 Extreme degenerate stars (mainly WD,NS, BH, …)

Extreme mass ratio inspirals
 Test Kerr black hole solution of GR Study galaxy nuclei

Cosmological backgrounds

University of Tokyo, March 12th, 201723

Worldwide strategy setting

Signal coincidence in different detectors will continue to be
crucial for GW astronomy=> International coordination is mandatoryGravitational Wave International Committee (GWIC)
 Representative from all detectors/projects» LIGO, Virgo, KAGRA, GEO, LISA, …



Gravitational Wave Agency Committee (GWAC)
 Promoted by NFS
 Representatives from funding agencies in several countries» US, Canada, Germany, France, Italy, Spain, UK, Australia» Japan is missing so far

University of Tokyo, March 12th, 201724

ConclusionFirst gravitational wave detection achieved!

Gravitational wave astronomy started!



20 years of effort with Initial detectors and Advanced detectors
 10 year cyclesAdvanced LIGO/Virgo upgrades being prepared

LISA on track to be launched in 2034 (earlier launch technicallypossible)

New ground based facilities discussed in Europe and in the US

GW science has a bright future

University of Tokyo, March 12th, 201725