The general theory of relativity is our most accurate description of gravitation
• Published by Einstein in 1915, this is a theory of gravity
• A massive object causes space to curve and time to slow down
• These effects manifest themselves as a gravitational force
• These distortions of space and time are most noticeable in the vicinity of large masses or compact objects
The general theory of relativity also predicts the existence of gravitational waves, which are ripples in the overall geometry of space and time produced by moving masses
Gravitational waves have been detected indirectly, and specializedantennas are under construction to make direct measurement of the gravitational waves from cosmic cataclysms
• If a stellar corpse has a mass greater than about 2 to 3 M, gravitational compression will overwhelm any and all forms of internal pressure
• The stellar corpse will collapse to such a high density that its escape speed exceeds the speed of light
Supermassive black holes exist at the centers
of most galaxies
• These are detected by observing the motions of material around the black hole
Falling into a black hole is an infinite voyage
● Could a black hole somehow be connected to another part of spacetime, or even some other universe?
● General relativity predicts that such connections, called wormholes, can exist for rotating black holes
Black holes evaporate
Black Holes have no Hair
Properties of a black hole:- Mass- Spin (angular momentum)- Charge (tends to be zero)
Black Holes can have impact on their environments
Do Black Holes Really Exist? Good Candidate: Cygnus X-1
- Binary system: 30 MSun star with unseen companion.
- Binary orbit => companion > 7 MSun.
- X-rays => million degree gas falling into black hole.
Vela satellite
An early gamma ray-burst
A Gamma Ray Burst Sampler
Great debate: 1967-1997
GRBM: 40-600 keVWFC: 2-30 keVNFI: 2-10 keV
Bepposax Satellite
X-Ray Afterglow from GRB 971214
t=6.5 hrs t=12.5 hrs t=54 hrs
Optical Afterglow from GRB 971214
Host
HST Image
Keck Images
2 days 2 months
Optical Afterglow from GRB 080319b
Swift Image
Light Curve
Naked-eye visible for ~30 sec. Distance = 7.5 billion ly
Uh-oh
GRB HostGalaxies
Bloom et al. 2002
Radio Light Curves from long GRBs
GRB 970508
• First VLBI detection of a GRB Afterglow • absolute position to < 1 mas• Size < 10^19 cm (3 lt years)• Distance > 10000 lt years
Taylor et al 1997
R ~ (E/n)^1/8
Relativistic Expansion v ~ 0.96c
E ~ 10^53 ergs (isotropic equivalent)
Taylor et al 2004Pihlstrom et al 2007
GRB Expansion
The Evidence (long The Evidence (long GRBs)GRBs)
● Peak toward low end of gamma-ray, complex gamma-ray light curves
● Often have bright afterglows
● Evidence for a relativistic explosion
● Energy required of ~ 1053 ergs (isotropic)
● Associated with regions of star formation in distant galaxies (out to edge of observable universe)
● Sometimes obscured by dust
● Plus …
Example Supernova: 1998bw
Long GRBs clearly connected to Supernovae
Hjorth et al 2003
1. White Dwarf If initial star mass < 8 M
Sun or so
2. Neutron Star If initial mass > 8 M
Sun and < 25 M
Sun
3. Black Hole If initial mass > 25 M
Sun
Final States of a Star
No Event + PN
Supernova + ejecta
GRB + Supernova + ejecta
Clicker Question:
What is the remnant left over from a GRB?
A: a white dwarf + expanding shell
B: a neutron star + expanding shell
C: a black hole + expanding shell
D: no remnant, just the expanding shell
Clicker Question:
Where do most GRBs occur:
A: in globular clusters
B: in star forming regions
C: in old open clusters
D: in the Oort cloud
Clicker Question:
What was the subject of the great debate about GRBs that went on for ~30 years?
A: If they were produced by Supernovae or colliding stars.
B: If they were galactic or extragalactic in origin.
C: If they were of terrestrial or extraterrestrial in origin?
D: If a nearby GRB killed off the dinosaurs.
Coalescence versus Collapse
NS-NS binary Massive star
cm 10100
15
r cm 10110
17
r
