Edmund Bertschinger MIT Department of Physics and Kavli Institute for Astrophysics and Space Research The Search for Black Holes and Gravitational Waves: The Ultimate Tests of Einstein’s Relativity

2 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)

3 Einstein’s Strangest Theory: Curved Space, Warped Time The gravity of massive objects can make space non-Euclidean: Cosmology: Black hole:

4 Are Black Holes Giant Spacetime Trampolines? Figure from NASA/GSFC Imagine What does Stephen Hawking say?

5 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!

6 i was considering how within night's loose sack a star's nibbling in- fin -i- tes- i -mal- ly devours darkness the hungry star which will e. -ven tu- al -ly jiggle the bait of dawn and be jerked into eternity. when over my head a shooting star Burs (t into a stale shriek like an alarm-clock) -- e.e. cummings Collapse through the horizon: N. Rumiano,

7 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

8 How can matter escape from a BH? Quantum tunneling produces a Particle-Antiparticle pair from the vacuum! 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!

9 Black holes in Nature The afterlife of giant stars Black hole masses 3-15 solar masses Giant sinkholes in galaxy centers Black hole masses million to billion solar masses

10 How we find black holes (and neutron stars): X-rays! MIT-led Rossi X-Ray Timing Explorer satellite, launched 1995

11 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 1 Artistic conception 2

12 How can we prove these are the BH of Einstein’s theory? Measure the gravitational waves emitted as two black holes merge.

13 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

14 Neutron Binary System – Hulse & Taylor (Nobel Prize) PSR Timing of pulsars   17 / sec Neutron Binary System separated by 10 6 miles m 1 = 1.4m  ; m 2 = 1.36m  ;  = Prediction from general relativity spiral in by 3 mm/orbit rate of change orbital period ~ 8 hr Gravitational waves — the Evidence

15 Left: Artist’s conception of gravitational waves produced by a binary system Bottom: LIGO design

16 Effect of a GW on matter

17 Global network of detectors LIGO LISA VIRGO TAMA GEO Detection confidence Source polarization Sky location AIGO

18 LIGO: Laser Interferometer Gravitational-wave Observatory LA WA 4 km 2 km 4 km

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20 Science Runs and Sensitivity S2 2 nd Science Run Feb - Apr 03 (59 days) S1 1 st Science Run Sept 02 (17 days) S3 3 rd Science Run Nov 03 – Jan 04 (70 days) LIGO Target Sensitivity Frequency (Hz) Strain (1/rtHz)  L  strain x 4000 m  m rms S3 Duty Cycle H169% H263% L122%

21 H1 strain sensitivity – S1 to S4+

22 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

23 Laser Interferometer Space Antenna (LISA, 2013+) 1 AU = 1.5x10 8 km  Three spacecraft  triangular formation  separated by 5 million km  Formation trails Earth by 20°  Approx. constant arm-lengths  Constant solar illumination

24 LISA and LIGO

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

26 Special Thanks to Prof. Nergis Mavalvala and the LIGO Scientific Collaboration YOU can get involved in LIGO data analysis: “Einstein at Home”

27 Additional Credits and Information Credits: Black hole animated gif courtesy Andrew J.S. Hamilton Rossi X-Ray Timing Explorer figure courtesy NASA/Goddard Space Flight Center LIGO and other gravitational wave images courtesy Nergis Mavalvala Stephen 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)