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Chapter 14 Notes: Black Holes
Astronomy
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I. Black Holes
 Neutron stars cannot exist with masses ____________________________
 We know of no mechanism to halt the collapse of a compact object with __________________
 It will collapse into a single point – a _____________________________
 a ________________ ________________________
II. Escape Velocity
 Velocity needed to escape Earth’s gravity from the surface: vesc ≈ 11.6 km/s
 Now, gravitational force decreases with distance (~ 1/d2) => Starting out high above the
surface => lower escape velocity
 If you could compress Earth to a smaller radius => higher escape velocity from the surface
III. The Schwarzchild Radius
=> There is a limiting radius where the escape velocity reaches the speed of light, c:
Write the equation for Rs
Rs is called the Schwarzchild Radius
Schwarzschild Radius and the Event Horizon
No object can travel faster than the ___________________________________________.
=> Nothing (not even light) can escape from inside the ______________________________ radius.
• We have no way of finding out what’s happening inside the Schwarzschild radius.
=> “______________ _________________”
IV. General Relativity Effects Near Black Holes
 At a __________________________, the gravitational fields of a black hole and a star of the same
mass are virtually identical
 At __________ distances, the much deeper gravitational potential will become noticeable.
 An astronaut descending down towards the event horizon of the BH will be
_______________________ vertically (tidal effects) and _____________________ laterally.
 This effect is called “_______________________________.”
B. Time Dilation
 Clocks closer to the black hole run more _______________________
 Time dilation becomes _______________________ at the event horizon
C. Gravitational Red Shift
All wavelengths of emissions from near the event horizon are ____________________ (red shifted).
 Frequencies are lowered
V. Observing Black Holes
No ________________ can escape a black hole
 Black holes can not be ______________________directly
 If an invisible compact object is part of a binary, we can estimate its _________ from the orbital
period and radial velocity
Mass > 3 Msun = Black Hole
VI. Black Hole vs Neutron Star Binaries
 Black Holes: Accreted matter___________________ beyond the event horizon without a trace
 Neutron Stars: Accreted matter produces _____________________________ as it impacts on the
neutron star surface
VII Black Hole X-Ray Binaries
 Accretion disks around black holes are strong ____________________ sources
 Rapidly, erratically _______________________ (with flickering on time scales of less than a second)
 Sometimes: Quasi-periodic oscillations (QPOs)
 Sometimes: _____________________-emitting jets
VIII Gamma-Ray Bursts (GRBs)
 Short (~ a few s), bright bursts of _________________________________
 Later discovered with X-ray and optical afterglows lasting several hours – a few days
 Many have now been associated with host ______________________ at large (cosmological)
distances.
 At least some GRBs are probably related to the _______________ of very massive (> 20 Msun)
stars
 In a supernova-like _____________________________ of stars this massive, the core might collapse
not to a neutron star, but directly to a black hole
 Such stellar explosions are termed “_____________________________________”
IX Magnetars
 Some ________________ _____________________ have magnetic fields ~ 100 times stronger even than
normal neutron stars. These care called Magnetars.
 ___________________________-like ruptures in the surface crust of Magnetars cause bursts of soft
gamma-rays.