Which of the following is closest in mass to a white dwarf star?
the sun
Which of the following is closest in size (radius) to a white dwarf star?
Earth
Which of the following statements about degeneracy pressure is FALSE?
degeneracy pressure depends on temperature
Which of the following statements about novae is FALSE?
Our Sun will probably undergo at least one nova when it becomes a white dwarf in 5 billion years.
Suppose that a white dwarf is gaining mass through accretion in a binary system. What happens if the mass someday reaches the 1.4 solar mass limit?
The white dwarf will explode completely as a white dwarf supernova.
In a white dwarf which has exceeded its mass limit, what occurs as it fuses carbon?
Temperature increases, pressure remains the same
After a massive-star supernova, what is left behind?
either a neutron star or a black hole
What is the upper limit to the mass of a neutron star?
about 3 solar masses
Which of the following is closest in size (radius) to a neutron star?
a city
Pulsars are thought to be ________.
rapidly rotating neutron stars
What causes the pulses of a pulsar?
As the star spins, it beams radiation into space. If a beam crosses Earth, we observe a pulse.
How is an X-ray burst (in a binary system) similar to a nova?
Both involve explosions on the surface of a star.
Which of the following statements best describes what is "relative" in the theory of relativity?
The theory says that measurements of motion make sense only when we state what they are
measured relative to.
The measured value of the speed of light is about 300,000 km/s. Suppose a futuristic space train is traveling toward you at 200,000 km/s with its headlights on. If you could measure the speed of the light from the headlights, you would find it to be _____
300,000 km/s
The speed of light slows down near a black hole. true/false
is false
According to general relativity, how is time affected by gravity?
Time runs slower in places where gravity is stronger.
How does the gravity of an object affect light?
Light coming to us from a compact massive object, such as a neutron star, will be redshifted.
Which of the following best describes the relationship between Newton's theory of gravity and Einstein's theory of general relativity?
Newton's theory tells us to think of gravity as a force, while general relativity tells us to think of
gravity as curvature of spacetime.
and
Newton's theory of gravity is an approximation to general relativity that works when gravity is
relatively weak,
What is the basic definition of a black hole?
an object with gravity so strong that not even light can escape
If the sun were squeezed enough to make it into a black hole, what would happen?
The Earth's orbit would be unchanged.
If you fall toward a black hole, is it possible for you to survive the tidal stretching near the black hole?
Yes, if the mass of the black hole is very large.
Suppose you drop a clock toward a black hole. As you look at the clock from far away, what will you notice?
Time on the clock will run slower as it approaches the black hole, and light from the clock will be increasingly redshifted.
The Sun's location in the Milky Way Galaxy is ________.
in the galactic disk, roughly halfway between the center and the outer edge of the disk
How do disk stars orbit the center of the galaxy?
They all orbit in roughly the same plane and in the same direction.
Compared with stars in the disk, orbits of stars in the halo
are elliptical, with random orientation.
Where does most star formation occur in the Milky Way today?
in the spiral arms
Which of the following analogies best describes how the structure of the galaxy's spiral arms is maintained?
Like cars slowing in traffic to look at an accident, stars slow as they pass through the spiral arms.
If we could watch spiral arms from a telescope situated above the Milky Way over 500 million years, what would we see happen?
Stars will move through the spiral arms, bunching up closer as they pass through. Young hot
stars will form and die within the arms before having a chance to move out.
In the formation of our galaxy, which of the following formed first?
globular clusters
The most basic difference between elliptical galaxies and spiral galaxies is that ________.
elliptical galaxies lack anything resembling the disk of a spiral galaxy
What is the best evidence for an extremely massive black hole in the center of the Milky Way?
The orbits of stars in the center of the galaxy indicate that the presence of 3- to 4-million-solar-
mass object in a region no larger than our Solar System.
A galaxy with little cool gas or dust and no evidence of ongoing star formation is most likely of which type?
elliptical galaxy
Why are Cepheid variables important?
Cepheids are pulsating variable stars, and their pulsation periods are directly related to their
luminosities. Hence, we can use Cepheids as "standard candles" for distance measurements.
What is a "standard candle"?
an object for which we are likely to know the true luminosity
Which of the following is a consequence of Hubble's Law?
he more distant a galaxy is from us, the faster it moves away from us
Does Hubble's law work well for galaxies in the Local Group? Why or why not?
No, because galaxies in the Local Group are gravitationally bound together.
Overall, what is the most accurate way to determine the distance to a nearby star?
stellar parallax
What do we study about a white dwarf supernova when it's used in a distance measurement technique?
How its apparent brightness changes in time
Which of the following sequences lists the methods for determining distance in the correct order from nearest to farthest?
parallax, main-sequence fitting, Cepheid variables, Tully-Fisher relation, Hubble's law
Two ways in which the starting conditions in a protogalactic cloud might cause it to become an elliptical (rather than spiral) galaxy are if the cloud begins with either
relatively slow rotation or relatively high density
Why should galaxy collisions have been more common in the past than they are today?
Galaxies were closer together in the past because the universe was smaller.
Collisions between two galaxies
can turn two spiral galaxies into one elliptical galaxy
Is it possible for the jets emitted by an active galactic nucleus to be larger than the "visible" galaxy (the part of the galaxy that contains stars)?
yes
What is a quasar?
the extremely bright center of a distant galaxy
The enormous power output from an active galaxy is due to
supermassive black hole that is accreting material
All of the following are true. Which of these gives evidence that quasars were more common in the early stages of the universe?
They are more common at very great distances.
Why do we believe that most of the mass of the Milky Way is in the form of dark matter?
The orbital speeds of stars far from the galactic center are surprisingly high.