LATEST ASTR 1020 EXAM / ASTR 1020 ACTUAL FINAL
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A teaspoon of white dwarf material on Earth would weigh... - ANSWER: a few tons
Suppose a white dwarf is gaining mass because of accretion in a binary system. What
happens if the mass someday reaches the 1.4 solar-mass limit? - ANSWER: The white
dwarf undergoes a catastrophic collapse, leading to a type of supernova that is
somewhat different from that which occurs in a massive star but is comparable in
energy
How does a 1.2 solar-mass white dwarf compare to a 1.0 solar-mass white dwarf? -
ANSWER: it has a smaller radius
A typical (one-solar-mass) white dwarf star is approximately the same size (diameter)
as _____. - ANSWER: Earth
What causes the radio pulses of a pulsar? - ANSWER: As the star spins, beams of
radio radiation sweep through space. If one of the beams crosses Earth, we observe
a pulse.
From an observational standpoint, what is a pulsar? - ANSWER: an object that emits
flashes of light several times per second or more, with near perfect regularity
After a massive star supernova, what is left behind? - ANSWER: either a neutron star
or a black hole
Which of the following is closest in size (radius) to a neutron star? - ANSWER: a city
You find a central object at the galactic center has a mass of about 3 million solar
masses but is not more than about 70 AUs in diameter -- which means it cannot be
much larger than the size of our planetary system. Why do these facts lead
astronomers to conclude that the central object is a black hole? - ANSWER: there is
no known way to pack so much mass into such a small volume without it collapsing
into a black hole
True or False? a typical neutron star is less massive than the Sun. - ANSWER: False
How do we know what happens at the event horizon of a black hole? - ANSWER: We
don't know for sure, we only know what to expect based on the predictions of
general relativity
, When we see X rays from an accretion disk in a binary system, we can't immediately
tell whether the accretion disk surrounds a neutron star or a black hole. Suppose we
then observe each of the following phenomena in this system. Which one would
force us to immediately rule out the possibility of a black hole? - ANSWER: sudden,
intense X ray bursts
No light can escape from a black hole. Therefore, to detect a black hole, we must
observe ____. - ANSWER: radiation coming from hot gas that is falling toward a black
hole
In general, we can detect a black hole left behind by a dead star _____. - ANSWER:
only if mass is being transferred to it by another star
An advanced civilization lives on a planet orbiting a close binary star system that
consists of a 15Msun red giant and a 10Msun black hole. Assume that the two stars
are quite close together, so that an accretion disk surrounds the black hole. The
planet on which the civilization lives orbits the binary star at a distance of 10 AU.
Sometime within the next million years or so, the planet is likely to be doomed
because... - ANSWER: the red giant will probably undergo a supernova explosion
within the next million years
An advanced civilization lives on a planet orbiting a close binary star system that
consists of a 15Msun red giant and a 10Msun black hole. Assume that the two stars
are quite close together, so that an accretion disk surrounds the black hole. The
planet on which the civilization lives orbits the binary star at a distance of 10 AU.
As you begin to read, you learn that the book describes the evolution of the people
living in the star system described above. You learn that these people evolved from
organisms that lived 5 billion years ago. Which of the following should you expect to
find as you continue to read? - ANSWER: they evolved on a different planet in a
different star system and moved to their current location.
Why do astronomers consider gamma-ray bursts to be one of the greatest mysteries
in astronomy? - ANSWER: because the current evidence suggests that they are the
most powerful bursts of energy that ever occur anywhere in the universe, but we
don't know how they are produced.
According to current theory, both nova explosions and X-ray bursts occur in binary
systems in which an ordinary star orbits either a white dwarf or a neutron star.
However, novae involve hydrogen fusion on the surface of a stellar corpse, while X-
ray bursts involve helium fusion. What can you conclude from this fact? - ANSWER:
X-ray bursts must occur on objects with much stronger surface gravity than those
that produce novae.
Which of these binary systems is most likely to contain a black hole? - ANSWER: an
X-ray binary containing an Ostar and another object of equal mass
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