“Understanding our Universe with Gravitational Waves”
Barry C Barish Caltech and UC Riverside LIGO-G1602199 2-Dec-2020 1 General Relativity and Gravitational Waves
Newton’s Theory of Einstein’s Theory of Gravity (1687) Gravity (1915)
Space and Time are unified in a force between Universal Gravity: four dimensional massive objects is directly proportional to the product of their masses, and spacetime inversely proportional to the square of the distanceLIGO-G1602199 between them. 2 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 Einstein Explains WHY the apple falls!
Earth distorts spacetime
4 Einstein Solves a Conceptual Problem with Newton’s Theory of Gravity “Instantaneous Action at a Distance”
5 Einstein Makes a ‘New’ Prediction
Einstein Eddington
"Not only is the universe stranger than we imagine, it is stranger than we can imagine. Sir Arthur Eddington 6 First observed during the solar eclipse of 1919 by Sir Arthur Eddington, when the Sun was silhouetted against the Hyades star cluster 7 8 In Modern Astronomy: Gravitational Lensing
Einstein Cross
9 Gravitational Lensing: The Einstein Cross
10 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 Earth Clocks faster = + 45 microsec/day
GPS Correction = + 38 microsec/day
(Accuracy required ~ 30 nanoseconds to give 10 meter resolution
11 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 gravitational radiation warpage at the speed of light binary inspiral of compact objects
12 Einstein’s Theory of Gravitation Gravitational Waves • Using Minkowski metric, the information about space- time curvature is contained in the metric as an added 1 ∂ 2 term, hµν. In the weak field limit, the equation can be ( 2 −∇ h = 0) described with linear equations. If the choice of gauge 2 ∂tc 2 µν is the transverse traceless gauge the formulation becomes a familiar wave equation
• 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 µν + −+−= czthczthh )/()/( from each other. x 13 Gravitational Waves
• Ripples of spacetime that stretch and compress spacetime itself L • The amplitude of the wave is h ≈ 10-21 • Change the distance between masses that are free to move by ΔL = h x L • S pacetime is “stiff” so changes in distance are very small ΔL
14 Suspended Mass Interferometry
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15 SitingLIGO LIGO Sites Project Approved 1994
16 ‘Direct’ Detection of Gravitational Waves LIGO Interferometers
Hanford, WA
Livingston, LA 17 What Limits LIGO Sensitivity?
- 18 Passive / Active Multi-Stage Isolation Advanced LIGO
19 Advanced LIGO GOALS Broadband, At ~40 Hz, Factor ~3 Factor improvement ~100 improvem enth
Better seismic isolation
Higher power laser Better test masses andLIGO suspension-G1602199 20 Black Hole Merger: GW150914
21 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
22 SitingLIGO LIGO Sites Project Approved 1994
23 Black Hole Merger: GW150914
24 Observed Binary Mergers
25 Searching for Electromagnetic Counterparts
26 20th Century : Multiwavelength Astronomy
Electromagnetic Spectrum
27 21st Century: “Combined Instrument”
28 Event Horizon Telescope Black Hole Image
29 Next Frontier: Multimessenger Astronomy Gravitational Waves Electromagnetic Neutrinos
30 The Network in mid-2020’s
Advanced Virgo 2016 Advanced LIGO Hanford, KAGRA Livingston 2019 2015 LIGO-India 2025
31 31 Improving Localization
2016-17 2017- 18
2019+ LIGO-P1200087-v32 (Public) 2024
32 Virgo Joins LIGO – August 14, 2017
For all 10 reported Black Hole Binary Event NO Electromagnetic counterparts found !!
33 And, on August 17
34 Fermi Satellite GRB detection 2 seconds later
35 170817A” Astrophys. J. Lett., 848:L13, (2017) Multi-messenger Astronomy with Gravitational Waves
Binary Neutron Star Merger
X-rays/Gamma-rays Gravitational Waves
Visible/Infrared Light Neutrinos Radio Waves
36 37 Observations Across the Electromagnetic Spectrum Birth of Multimessenger Astronomy
“Kilonova”
38 Light Curves
39 Kilonova Emission
40 Origin of the Heavy Elements
41 NS Mergers are Incredible Gold Factories
LIGO observed Neutron Star Merger produced ~ 100 Earth Masses of Gold
42 Detector Performance: BNS range
43 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: Exceptional Events
46 47 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
48 Gravitational Wave Frequency Coverage
49 LISA: Laser Interferometer Space Array
Three Interferometers
2.5 106 km arms
50 Pulsar Timing Arrays
51 Signals from the Early Universe stochastic background
Cosmic Microwave background
WMAP
52 Gravitational Waves: Birth of a New Astronomy
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