Question 1

How do we know what happens at the event horizon of a black hole?

Accepted Answer

A)  Physicists have created miniature black holes in the lab. 
B)  Astronomers have sent spacecraft through the event horizon of a nearby black hole. 
C)  Astronomers have analyzed the light from matter within the event horizon of many black holes. 
D)  Astronomers have detected X-rays from accretion disks around black holes. 
E)  We don't know for sure: we only know what to expect based on the predictions of general relativity.

Question 2

Evidence that Pulsars are Neutron Stars: Suppose a friend of yours insists that pulsars are artificial time-signals constructed by aliens. List and explain all of the observational evidence that pulsars are actually natural phenomena, namely rapidly spinning neutron stars.

Accepted Answer

The answer of Evidence that Pulsars are Neutron Stars: Suppose...

Question 3

Which of the following statements about novae is not true?

Accepted Answer

A)  A star system that undergoes a nova may have another nova sometime in the future. 
B)  A nova involves fusion taking place on the surface of a white dwarf. 
C)  Our Sun will probably undergo at least one nova when it becomes a white dwarf about 5 billion years from now. 
D)  When a star system undergoes a nova, it brightens considerably, but not as much as a star system undergoing a supernova. 
E)  The word nova means "new star" and originally referred to stars that suddenly appeared in the sky, then disappeared again after a few weeks or months.

Question 4

If you were to come back to our Solar System in 6 billion years, what might you expect to find?
A) a red giant star
B) a white dwarf
C) a rapidly spinning pulsar
D) a black hole
E) everything will be essentially the same as it is now

Accepted Answer

The answer of If you were to come back to...

Question 5

Prior to 1991, most astronomers assumed that gamma-ray bursts came from neutron stars (with accretion disks) within the Milky Way Galaxy. How do we now know that this hypothesis was wrong?

Accepted Answer

A)  We now know that gamma-ray bursts come not from neutron stars but from black holes. 
B)  Theoretical work has proven that gamma rays cannot be produced in accretion disks. 
C)  Observations from the Compton Gamma-Ray Observatory showed that gamma-ray bursts come randomly from all directions in the sky. 
D)  Observations from the Compton Gamma-Ray Observatory showed that gamma-ray bursts occur too frequently to be attributed to neutron stars. 
E)  Observations from the Compton Gamma-Ray Observatory allowed us to trace gamma-ray bursts to pulsating variable stars in distant galaxies.

Question 6

Which of the following is not true about differences between novae and supernovae?

Accepted Answer

A)  Supernovae eject gas into space but novae do not. 
B)  Novae are much less luminous than supernovae. 
C)  Novae occur only in binary star systems, while supernovae can occur both among single stars and among binary star systems. 
D)  The same star can undergo novae explosions more than once, but can undergo only a single supernova.

Question 7

A 10 solar mass main sequence star will produce which of the following remnants?

Accepted Answer

A)  white dwarf 
B)  neutron star 
C)  black hole 
D)  none of the above

Question 8

Which of the following best describes what would happen if a 1.5 solar mass neutron star, with a diameter of a few kilometers, were suddenly to appear in your hometown?

Accepted Answer

A)  The entire mass of the Earth would end up as a thin layer, about 1 cm thick, over the surface of the neutron star. 
B)  It would rapidly sink to the center of the Earth. 
C)  The combined mass of the Earth and the neutron star would cause the neutron star to collapse into a black hole. 
D)  It would crash through the Earth, creating a large crater, and exit the Earth on the other side. 
E)  It would crash into the Earth, throwing vast amounts of dust into the atmosphere which in turn would cool the Earth. Such a scenario is probably what caused the extinction of the dinosaurs.

Question 9

Consider again the civilization described in the previous question. (They live on a planet orbiting 10 AU from a close binary star system that consists of a 15 MSᵤn red giant star and a 10 MSᵤn black hole surrounded by an accretion disk.) One foolhardy day, a daring individual in their space force (let's call him Major Tom) decides to become the first of his species to cross the event horizon of the black hole. To add to the drama, he decides to go in wearing only a thin space suit, which offers no shielding against radiation, no cushioning against any forces, and so on. Which of the following is most likely to kill him first (or at least to start the process of killing him first)?

Accepted Answer

A)  X-rays from the accretion disk 
B)  Tidal forces due to the black hole 
C)  The crush of gravity at the singularity embedded within the black hole 
D)  The sucking force from the black hole, which will cause his head to explode

Question 10

All pulsars are neutron stars, but not all neutron stars are pulsars.

Accepted Answer

A) True 
 B)False

Question 11

Which of the following is closest in size (radius) to a neutron star?

Accepted Answer

A)  the Earth 
B)  a city 
C)  a football stadium 
D)  a basketball 
E)  the Sun

Question 12

Imagine what would happen if Jupiter was suddenly replaced by a black hole with the same mass as Jupiter.

Accepted Answer

A)  The other planets would slowly be pulled into Jupiter, but the Sun would be unaffected. 
B)  The orbits of the solar system would be unaffected (including Jupiter's) 
C)  The entire solar system would instantly be sucked into the black hole. 
D)  The other planets and the Sun would slowly be pulled into Jupiter.

Question 13

Rank the following 4 items in order of increasing density (low to high).

Accepted Answer

A)  Main sequence star, white dwarf, neutron star, black hole singularity 
B)  Main sequence star, black hole singularity, neutron star, white dwarf 
C)  Main sequence star, neutron star, white dwarf, black hole singularity 
D)  Black hole singularity, main sequence star, white dwarf, neutron star

Question 14

A paperclip with the density of a neutron star would weigh (on the Earth)

Accepted Answer

A)  about the same as a regular paperclip. 
B)  a few tons. 
C)  more than Mt. Everest. 
D)  more than the Moon. 
E)  more than the Earth.

Question 15

After a massive-star supernova, what is left behind?

Accepted Answer

A)  Always a white dwarf 
B)  Always a neutron star 
C)  Always a black hole 
D)  Either a white dwarf or a neutron star 
E)  Either a neutron star or a black hole

Question 16

Pulsars are thought to be ________.

Accepted Answer

A)  accreting white dwarfs 
B)  rapidly rotating neutron stars 
C)  unstable high-mass stars 
D)  accreting black holes

Question 17

More massive white dwarfs are smaller than less massive white dwarfs

Accepted Answer

A) True 
 B)False

Question 18

A white dwarf is ________.

Accepted Answer

A)  what most stars become when they die 
B)  a precursor to a black hole 
C)  an early stage of a neutron star 
D)  a brown dwarf that has exhausted its fuel for nuclear fusion

Question 19

Which of the following statements about gamma ray bursts is not true?

Accepted Answer

A)  Based on their distribution in the sky, we can rule out a connection between gamma ray bursts and X-ray binaries in the Milky Way Galaxy. 
B)  Gamma ray bursts are among the most luminous events that ever occur in the universe. 
C)  The events responsible for gamma ray bursts apparently produce only gamma rays, and no other light that we can hope to detect. 
D)  Gamma ray bursts were originally discovered by satellites designed to look for signs of nuclear bomb tests on Earth.

Question 20

Each Voyager spacecraft carries a "postcard" designed to be understandable to any aliens that might someday encounter it. On the "postcard," scientists pinpointed the location of Earth by triangulating it between pulsars. Why did the scientists choose pulsars rather than some other type of star?

Accepted Answer

A)  Pulsars are easy to identify by their almost perfectly steady periods of pulsation. 
B)  Pulsars are very bright and therefore easy to find. 
C)  Several pulsars are located within a dozen light-years of our solar system, making them useful for finding our solar system. 
D)  We're pretty sure that aliens will have only radio telescopes and not optical telescopes, so they'll have a better chance of seeing pulsars than ordinary stars.

Exam 13: Bizarre Stellar Graveyard