Question : 61.The event horizonA.is believed to be a singularity.B.is a crystalline : 1777250

61.The event horizon
A.is believed to be a singularity.
B.is a crystalline layer.
C.has a radius equal to the Schwarzschild radius.
D.marks the inner boundary of a planetary nebula.
E.is located at the point where synchrotron radiation is created around a pulsar.

62.An isolated black hole in empty intergalactic space would be difficult to detect because
A.there would be no stars behind it whose light it could bend or lens gravitationally
B.it could not emit light from inside its event horizon
C.no companion stars would be affected by its gravitational field
D.no matter would be falling into it to create an x-ray emitting accretion disk
E.All of the above

63.Cygnus X-1 and LMC X-3 are black holes if the masses of the unseen companions are
A.less than 5 solar masses.
B.more than 5 solar masses.
C.between 0.4 and 1.4 solar masses.
D.less than 0.4 solar masses
E.not larger than the masses of the stars that we can see.

64.The peculiar system SS 433

I.	is emitting beams of energy and matter.
II.	is producing a spectrum with both a red and a blue shift.
III.	probably contains an accretion disk.
IV.	is the result of a planetary nebula.

A.I
B.III
C.II & III
D.I, II, & III
E.I, II, III, & IV

65.Which of the following objects is considered to possibly contain a black hole?
A.The central star of the Crab nebula
B.The Orion nebula.
C.LMC X-3
D.Algol
E.PSR 1257+12

66.The orbit of the binary pulsar, PSR 1936+16, studied by Taylor and Hulse
A.is so small that the orbital period is smaller than the pulsar period.
B.is growing smaller, presumably by emitting gravitational waves.
C.provides evidence that it is being orbited by at least 6 planets the size of Jupiter.
D.shows large changes each time an X-ray burst is emitted from the system.
E.contains a white dwarf and a black hole.

67.The density of a ___________ is greater than the density of a ___________.
A.white dwarf, neutron star
B.neutron star, black hole
C.pulsar, neutron star
D.pulsar, white dwarf
E.white dwarf, black hole

68.The search for black holes involves searching for
A.single stars that emit large amounts of X-rays.
B.X-ray binaries where the compact companion has a mass in excess of 3 .
C.large spherical regions from which no light is detected.
D.pulsars with periods less than one millisecond.
E.pulsars that are orbited by planets.

69.The material that accretes onto a neutron star or black hole is expected to emit X-rays because
A.the material will produce synchrotron radiation.
B.hydrogen nuclei begin to fuse and emit high energy photons.
C.the material will become hot enough that it will radiate most strongly a X-ray wavelengths.
D.as the material slows down it converts thermal energy to gravitational potential energy.
E.none of the above

70.Why don't all supernova remnants contain pulsars?
A.All supernova remnants do contain pulsars.
B.Some supernova explosions form white dwarfs instead of the neutron stars necessary for pulsars.
C.Pulsars slow down and quite producing the pulses before the supernova remnant dissipates.
D.The pulsar may be tipped so that the beams do not sweep past Earth.
E.b and c above.