Edmund Bertschinger

MIT Department of Physics andKavli Institute for Astrophysics and

Space Research

The Search for Black Holes and Gravitational Waves:

The Ultimate Tests of Einstein’s Relativity

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What is a black hole?

A massive spacetime curvature singularity,

Surrounded by an event horizon

(a point or ring of infinite density and tidal acceleration)

(a spacetime boundary between causally disconnected regions of the universe)

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Einstein’s Strangest Theory:Curved Space, Warped Time

The gravity of massive objects can make space non-Euclidean:

Cosmology:

Black hole:

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Are Black Holes Giant Spacetime Trampolines?

Figure from NASA/GSFC Imagine

What does Stephen

Hawking say?

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Einsteinian time warps

Minkowski diagram without a black hole

x

ct

y

My worldline (trajectory)

If you pass inside this cone, I can communicate with you!

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i was considering howwithin night's loosesack a star'snibbling in-fin-i-tes-i-mal-ly devoursdarkness thehungry starwhichwill e.-ventu-al-ly jigglethe bait ofdawn and be jerkedintoeternity. when over my head ashootingstarBurs(tinto a stale shrieklike an alarm-clock)

-- e.e. cummings

Collapse through the horizon:N. Rumiano,http://nrumiano.free.fr/Eindex.html

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What happens at the event horizon?

Classically, nothing — it’s just a dangerous border crossing.

Quantum mechanically, Hawking radiation Particle vacuum state fluctuates with creation/annihilation

of virtual pairs of particles Negative energy particles fall in, positive energy ones

escape, black hole loses mass as blackbody radiation Completely negligible for astrophysical black holes

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How can matter escape from a BH?

Quantum tunneling produces a Particle-Antiparticle pair from the vacuum!http://superstringtheory.com/blackh/blackh3.html

Hawking radiation is extremely weak and may never be observed. Yet it raises profound questions of quantum gravity that perhaps only Superstring Theory will be able to answer!

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Black holes in Nature

The afterlife of giant starsBlack hole masses 3-15 solar masses

Giant sinkholes in galaxy centersBlack hole masses million to billion

solar masses

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How we find black holes (and neutron stars): X-rays!

MIT-ledRossiX-Ray TimingExplorersatellite,launched 1995

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How do black holes emit X-rays?

They get indigestion from eating a companion star, which gets compressed and heated in an accretion disk!

Artistic conception 1Artistic conception 2

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How can we prove these are the BH of Einstein’s theory?

Measure the gravitational waves emitted as two black holes merge.

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Gravitational Radiation

Newtonian gravity is action at a distance, in clear violation of the principle of relativity. How does general relativity fix this? By adding WAVES that travel at the speed of light

How are they produced and how are scientists preparing to detect them? Produced by accelerating masses: for example, two black holes

merging Detected by their TINY effect on test masses, using LASERS

bouncing back and forth between moving mirrors

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Neutron Binary System – Hulse & Taylor (Nobel Prize)PSR 1913 + 16 -- Timing of pulsars

17 / sec

Neutron Binary System• separated by 106 miles• m1 = 1.4m; m2 = 1.36m; = 0.617

Prediction from general relativity• spiral in by 3 mm/orbit• rate of change orbital period

~ 8 hr

Gravitational waves — the Evidence

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Left: Artist’s conception of gravitational waves produced by a binary system

Bottom: LIGO design

http://www.ligo.caltech.edu/

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Effect of a GW on matter

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Global network of detectors

LIGO

LIGO

LISA

VIRGO

TAMA

GEO

• Detection confidence• Source polarization• Sky location

AIGO

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LIGO: Laser Interferometer Gravitational-wave

Observatory

3030 km(±10 ms)

LA

WA

4 km

2 km

4 km

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Science Runs and Sensitivity

S22nd Science Run

Feb - Apr 03(59 days)

S11st Science Run

Sept 02(17 days)

S33rd Science RunNov 03 – Jan 04

(70 days)

LIGO Target Sensitivity

Frequency (Hz)

Str

ain

(1/r

tHz)

L strain x 4000 m 10-18 m rms

S3 Duty Cycle

H1 69%

H2 63%

L1 22%

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H1 strain sensitivity – S1 to S4+

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What’s the latest? S5 (goals) Sensitivity (in terms of inspiral reach)

H1 11 Mpc (10 to 14 Mpc) H2 5 Mpc (6 to 9 Mpc) L1 11 Mpc (10 to 14 Mpc)

Stability and duty cycle 70% individual 40% triple coincidence

Schedule Started in November, 2005 Get 1 year of data at design sensitivity Enhancements over next 3 years

Advanced LIGO: 2008, 15 times more sensitive than initial LIGO

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Laser Interferometer Space Antenna (LISA, 2013+)

1 AU = 1.5x108 km

Three spacecraft triangular formation separated by 5 million km

Formation trails Earth by 20° Approx. constant arm-lengths Constant solar illumination

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LISA and LIGO

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Ultimate success…New Instruments, New Field, the Unexpected…

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Special Thanks to

Prof. Nergis Mavalvala and the LIGO Scientific Collaboration

YOU can get involved in LIGO data analysis: “Einstein at Home”

http://einstein.phys.uwm.edu/

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Additional Credits and InformationCredits:

Black hole animated gif courtesy Andrew J.S. HamiltonRossi X-Ray Timing Explorer figure courtesy NASA/Goddard

Space Flight CenterLIGO and other gravitational wave images courtesy Nergis

MavalvalaStephen Hawking’s voice was simulated and used without

permission.

Books:The Elegant Universe: Superstrings, Hidden Dimensions, and

the Quest for the Ultimate Theory, Brian Greene (more advanced than The Fabric of the Cosmos)

Black Holes and Time Warps: Einstein’s Outrageous Legacy, Kip S. Thorne (more advanced)