Transcript 1. black hole -

1. black hole • region of space where the pull of gravity is
so great that even light cannot escape.
• Possible end of a very massive star.
2. event horizon • imaginary spherical surface surrounding a
collapsing star within which no event can be
detected by an outside observer
3. gamma-ray burster • object that radiates huge amounts of energy
in the form of gamma rays, believed to be
due to the accretion of matter onto a neutron
star.
4. gravitational red shift • A prediction of Einstein’s theory of
relativity.
• Photons lose energy when they escape the
huge gravity of a massive object. This
energy loss decreases the frequency,
correspondingly increasing the wavelength.
5. lighthouse model • Leading explanation for pulsars. Region
near magnetic pole of pulsar emits a steady
stream of radiation which sweeps past Earth
each time the star rotates.
6. millisecond pulsar • Pulsar with a period indicating that the
neutron start is rotating nearly 1000 times a
second.
• Probably ‘spun up’ by drawing in matter
from a companion star.
7. neutron star • Dense ball of neutrons that remains at core
of star after a supernova explosion has
destroyed the rest of the star.
8. photon sphere • Imaginary sphere surrounding a black hole
at 1.5 times the Schwarzschild radius where
photons move in a circular orbit.
9. Principle of Cosmic
Censorship • Nature always hide any singularity, such as
a black hole, inside an event horizon, which
prevents the universe from seeing inside a
singularity.
10. pulsar • Object that emits radiation in the form of
rapid pulses with a characteristic pulse
period and duration. Charged particles flow
along the magnetic field lines of a rapidly
rotating neutron star, producing a beam of
radiation.
11. pulsar glitch • Small drop in teh period of a pulsar. Occur
when teh thin crust on a neutron stars
surface cracks and settles slightly atop the
superfluid interior.
12. Schwarzschild radius • Distance from the center of an object such
that, if all the mass were compressed within
that region, the escape velocity would equal
the speed of light.
• An object smaller than this radius is a black
hole.
13. singularity • A point in the universe where the density of
matter and the gravitational field are
infinite, such as at the center of a black
hole.
14. starquake • A cracking and resettling of the crust of a
neutron star, slightly reducing the radius of
the star. The spin rate increases, causing a
pulsar glitch.
15. superconductor • A material that conducts electricity without
resistance. The interior of a neutron star
may be a superconductive material.
16. superfluid • A material that flows without friction.
• The interior of a neutron star may be a
superfluid material.
17. theory of relativity • Einstein’s theory, forms the basis of most of
modern physics.
• Two essential facts:
1) nothing travels faster than light and
2) everything is affected by gravity.
18. time dilation • To an outside observer, a clock lowered into
a strong gravitational field will appear to
run slow. A prediction of the theory of
relativity.
19. x-ray burster • A neutron star accretes matter onto its
surface until temperatures reach the level
needed to cause hydrogen fusion. Results
in a sudden period of rapid nuclear burning.
1. How does the way in which a
neutron star forms determine
some of its basic properties?
• The amount of matter and amount of
collapse determines the spin rate of the
neutron star.
• This determines its pulse rate and pulse
period if it forms a pulsar.
2. How can we observe objects
as small as neutron stars?
• By observing pulsars.
3. Why arent all neutron stars
seen as pulsars?
• The beam that is emitted by the neutron star
must pass over the Earth to be detected as a
pulsar.
4. What are x-ray bursters?
• A neutron binary that accretes material
from its companion. As the gas builds up, it
eventually becomes hot enough to fuse
hydrogen. At this point a sudden period of
rapid nuclear burning releases a great deal
of energy in a brief, intense flash of x-rays.
5. What is the favored
explanation for the fast spin
rates of millisecond pulsars?
• That the neutron star has been ‘spun up’ by
drawing in matter from a companion star.
6. How might some neutron stars
have come to be members of
binary systems?
• The supernova progenitor must have lost a
lot of mass before the explosion, or a neutron
star may displace one member of a
preexisting binary system.
7. How might a pulsar acquire
planets?
• One possibility is that the binary companion
may have been destroyed by the energy and
gravity of the neutron star. The resulting
matter may have cooled into planets.
8. Use your knowledge of escape
velocity to explain why black
holes are said to be ‘black’?
• A black hole is so collapsed that the escape
velocity has exceeded the speed of light.
Therefore, nothing, not even light, can
escape.
9. Why is it so difficult to test the
predictions of general relativity?
• Because its effects on the Earth and the solar
system are so small.
10. Describe two tests of general
relativity.
• Light from a star is deflected as it passes
close to the Sun.
• Planetary orbits deviate from the perfect
ellipses of Kepler’s laws.
11. What would happen to
someone falling into a black
hole? Why?
• The person would be vertically stretched
and horizontally squeezed. They would be
literally torn to pieces. The tidal forces are
very different even over the length of a
body. Spaghettification.
12. Explain how a black hole
can evaporate?
• I don’t want to go into this.
• It was suggested by Stephen Hawking years
ago, but now even he doesn’t believe it
occurs
13. What makes Cygnus X-1 a
good black hole candidate?
• It releases x-rays, probably from an
accretion disk. The unseen companion
exceeds the mass normally accepted for
neutron stars, which means it is probably a
black hole.