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
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The general theory of relativity is our most accurate description of gravitation
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 specialized
antennas are under construction to make direct measurement
of the gravitational waves from cosmic cataclysms
Supermassive black holes exist at the centersof most galaxies
Falling into a black hole is an infinite voyage
Black holes evaporate
Black Holes have no Hair
Properties of a black hole:
- 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.
An early gamma ray-burst
A Gamma Ray Burst Sampler
Great debate: 1967-1997
Naked-eye visible for ~30 sec. Distance = 7.5 billion ly
Bloom et al. 2002
Taylor et al 1997
Relativistic Expansion v ~ 0.96c
E ~ 10^53 ergs
R ~ (E/n)^1/8
Taylor et al 2004
Pihlstrom et al 2007
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
Example Supernova: 1998bw
Long GRBs clearly connected to Supernovae
Hjorth et al 2003
Final States of a Star
1. White Dwarf
If initial star mass < 8 MSun or so
2. Neutron Star
If initial mass > 8 MSun and < 25 MSun
3. Black Hole
If initial mass > 25 MSun
No Event + PN
Supernova + ejecta
GRB + Supernova + ejecta
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
Where do most GRBs occur:
A: in globular clusters
B: in star forming regions
C: in old open clusters
D: in the Oort cloud
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