“Understanding our Universe with Gravitational Waves”

LIGO-G16021991

Barry C BarishCaltech and UC Riverside

2-Dec-2020

“Understanding our Universe with Gravitational Waves”

LIGO-G16021992

Universal Gravity: force between massive objects is directly proportional to the product of their masses, and inversely proportional to the square of the distance between them.

Space and Time are unified in a four dimensionalspacetime

Newton’s Theory of Gravity (1687)

Einstein’s Theory of Gravity (1915)

General Relativity and Gravitational Waves

Mercury's elliptical path around the Sun. Perihelion shifts forward with each pass. (Newton 532 arc-sec/century vs Observed 575 arc-sec/century)

(1 arc-sec = 1/3600 degree).3

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Einstein Explains WHY the apple falls!

Earth distorts spacetime

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Einstein Solves a Conceptual Problem with Newton’s Theory of Gravity

“Instantaneous Action at a Distance”

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"Not only is the universe stranger than we imagine, it is stranger than we can imagine.

Einstein Eddington

Sir Arthur Eddington

Einstein Makes a ‘New’ Prediction

First observed during the solar eclipse of 1919 by Sir Arthur Eddington, when the Sun was silhouetted against the Hyades star cluster

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In Modern Astronomy: Gravitational Lensing

Einstein Cross

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Gravitational Lensing: The Einstein Cross

GPS: General Relativity in Everyday Life Special Relativity (Satellites v = 14,000 km/hour“moving clocks tick more slowly”Correction = - 7 microsec/day

General Relativity Gravity: Satellites = 1/4 x EarthClocks faster = + 45 microsec/day

GPS Correction = + 38 microsec/day

(Accuracy required ~ 30 nanosecondsto give 10 meter resolution

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Einstein’s Theory Contains Gravitational Waves

A necessary consequence of Special Relativity with its finite speed for information transfer

Gravitational waves come from the acceleration of masses and propagate away from their sources as a space-time warpage at the speed of light

gravitational radiationbinary inspiral

of compact objects

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Einstein’s Theory of GravitationGravitational Waves

0)1( 2

2

22 =

∂∂

−∇ µνhtc

• Using Minkowski metric, the information about space-time curvature is contained in the metric as an added term, hµν. In the weak field limit, the equation can be described with linear equations. If the choice of gauge is the transverse traceless gauge the formulation becomes a familiar wave equation

)/()/( czthczthh x −+−= +µν

• The strain hµν takes the form of a plane wave propagating at the speed of light (c).

• Since gravity is spin 2, the waves have two components, but rotated by 450 instead of 900

from each other.

Gravitational Waves• Ripples of spacetime that stretch and

compress spacetime itself• The amplitude of the wave is h ≈ 10-21

• Change the distance between masses that are free to move by ΔL = h x L

• Spacetime is “stiff” so changes in distance are very small

L

ΔL

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Suspended Mass Interferometry

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Siting LIGOLIGO SitesProject Approved 1994

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Hanford, WALivingston, LA

‘Direct’ Detection of Gravitational WavesLIGO Interferometers

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What Limits LIGO Sensitivity?

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Passive / Active Multi-Stage IsolationAdvanced LIGO

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LIGO-G1602199

Better seismic isolation

Higherpowerlaser

Better test masses

and suspension

Advanced LIGO GOALS At ~40 Hz,

Factor ~100

improvementh

Broadband,Factor ~3

improvement

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Black Hole Merger: GW150914

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Measuring the parameters• Orbits decay due to emission of gravitational waves

– Leading order determined by “chirp mass”

– Next orders allow for measurement of mass ratio and spins– We directly measure the red-shifted masses (1+z) m– Amplitude inversely proportional to luminosity distance

• Orbital precession occurs when spins are misaligned with orbital angular momentum – no evidence for precession.

• Sky location, distance, binary orientation information extracted from time-delays and differences in observed amplitude and phase in the detectors

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Siting LIGOLIGO SitesProject Approved 1994

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Black Hole Merger: GW150914

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Observed Binary Mergers

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Searching for Electromagnetic Counterparts

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20th Century : Multiwavelength Astronomy

Electromagnetic Spectrum

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21st Century: “Combined Instrument”

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Event Horizon Telescope Black Hole Image

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Next Frontier: Multimessenger Astronomy

Electromagnetic NeutrinosGravitational Waves

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The Network in mid-2020’s

Advanced LIGO Hanford,Livingston 2015

Advanced Virgo2016

LIGO-India2025

KAGRA2019

Improving Localization

2016-17 2017-18

2019+ 2024LIGO-P1200087-v32 (Public)

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Virgo Joins LIGO – August 14, 2017

For all 10 reportedBlack Hole Binary Event NO Electromagnetic counterparts found !!

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And, on August 17

170817A” Astrophys. J. Lett., 848:L13, (2017)

Fermi Satellite GRB detection 2 seconds later

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Multi-messenger Astronomy with Gravitational Waves

X-rays/Gamma-raysGravitational Waves

Binary Neutron Star Merger

Visible/Infrared Light

Radio Waves

Neutrinos

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Observations Across the Electromagnetic SpectrumBirth of MultimessengerAstronomy

“Kilonova”

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Light Curves

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Kilonova Emission

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Origin of the Heavy Elements

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NS Mergers are Incredible Gold Factories

LIGO observed Neutron Star Merger produced

~ 100 Earth Masses of Gold

Detector Performance: BNS range

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Observed Gravitational Wave Events• 67 events total• O1 3 events• O2 8 events• O3 56 events• O4 next year

~1 event/day

G1901608-v2 44

Exceptional Events

LIGO-Virgo O3 public alerts:

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Exceptional Events

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Proposed 3rd Generation Detectors

Einstein Telescope 10 km

The Einstein Telescope: x10 aLIGO• Deep Underground; • 10 km arms• Triangle (polarization)• Cryogenic• Low frequency configuration• high frequency configuration

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Gravitational Wave Frequency Coverage

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LISA: Laser Interferometer Space Array

ThreeInterferometers

2.5 106 km arms

Pulsar Timing Arrays

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Signals from the Early Universe

Cosmic Microwavebackground

WMAP

stochastic background

Gravitational Waves: Birth of a New Astronomy

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