Astronomy 5 Final Exam

Remaining 35 questions

What happens when the gravity of a massive star is able to overcome neutron degeneracy pressure?

The core contracts and becomes a black hole

After a supernova event, what is left behind?

either a neutron star or a black hole

Why is Supernova 1987A particularly important to astronomers?

It is the nearest supernova detected in nearly 400 years

White dwarfs are so called because

they are both very hot and very small

What kind of pressure supports a white dwarf?

electron degeneracy pressure

How does a 1.2-solar-mass white dwarf compare to a 1.0-solar-mass white dwarf?

It has a smaller radius

Which of the following is closest in size (radius) to a white dwarf?

Earth

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

a city

From a theoretical standpoint, what is a pulsar?

a rapidly rotating neutron star

What is the basic definition of a black hole?

any object from which the escape velocity exceeds the speed of light

Which of the following statements about black holes is not true?

If the Sun magically disappeared and was replaced by a black hole of the same mass, Earth would soon be sucked into the black hole

If you were to come back to our Solar System in 6 billion years, what might you expect to find?

a white dwarf

What is the diameter of the disk of the Milky Way?

100,000 light-years

Which of the following comprise the oldest members of the Milky Way?

global clusters

What produces the 21-cm line that we use to map out the Milky Way Galaxy?

atomic hydrogen

Approximately how long does it take the Sun to orbit the Milky Way Galaxy?

230 million years

Which constellation lies in the direction toward the galactic center?

Sagittarius

Compared to spiral galaxies, elliptical galaxies are

redder and rounder.

The disk component of a spiral galaxy includes which of the following parts?

spiral arms

Why are Cepheid variables important?

Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use Cepheids as "standard candles" for distance measurements.

What is Hubble's law?

The recession velocity of a galaxy is directly proportional to its distance from us.

What is the most accurate way to determine the distance to a very distant irregular galaxy?

using a white-dwarf supernova as a standard candle

Based on current estimates of the value of Hubble's constant, how old is the universe?

between 12 and 16 billion years old

I observe a galaxy that is 100 million light-years away: what do I see?

the light from the galaxy as it was 100 million years ago and it is redshifted

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

What is a quasar?

the extremely bright center of a distant galaxy, thought to be powered by a massive black hole

What is meant by "dark energy"?

the agent causing the universal expansion to accelerate

The distribution of the dark matter in a spiral galaxy is

approximately spherical and about ten times the size of the galaxy halo.

If all the "dark matter" in the Universe were to be, somehow, instantaneously removed, which of the following would not happen?

The Solar System would fly apart.

What is the evidence for an accelerating universe?

White-dwarf supernovae are slightly dimmer that expected for a coasting universe.

To date, physicists have investigated the behavior of matter and energy at temperatures as high as those that existed in the universe as far back as ________ after the Big Bang.

10-10 second

What do we mean by inflation?

a sudden expansion of the universe after the strong force froze out from the GUT force

What kinds of atomic nuclei formed during the era of nucleosynthesis?

hydrogen and helium and trace amounts of deuterium and lithium

Why did the era of nuclei end when the universe was about 300,000 years old?

The universe had expanded and cooled to a temperature of about 3,000 K, cool enough for stable, neutral atoms to form.

Olbers' paradox is an apparently simple question, but its resolution suggests that the universe is finite in age. What is the question?

Why is the sky dark at night?