ASTR 104 – January 2008 Wintersession – Test 2

Questions on material that we have not covered are greyed out. Blue questions refer to test 3 material.

Multiple-Choice Questions

(1) What is the biggest mass a black hole can have?
a. 1.4 solar masses.
b. 3 solar masses.
c. 100 solar masses.
d. There is no maximum black hole mass.

(2) What kinds of stars are more common in our neighborhood?
a. Neutron stars.
b. Large, bright, supergiant stars.
c. Colder and dimmer stars than the Sun.
d. Small but very bright white dwarf stars.

(3) Is it common for two stars to be so close that they orbit around each other?
a. No, stars do not orbit around each other, only planets orbit around stars.
b. No, only about 1% of stars are sufficiently close to each other.
c. Yes, possibly about half of all stars are that close to each other.
d. Yes, every star revolves around one or more other stars.

(4) What is Einstein's general theory of relativity about?
a. Electric and magnetic forces between elementary particles.
b. The nuclear reactions that occur in the cores of massive stars.
c. The fact that gravity is produced by the curvature of spacetime.
d. The fact that objects spin faster when they contract to small sizes.

(5) Which of the following is likely to be happening in the center of a planetary nebula?
a. A star is nearing the end of its life.
b. A planet is being formed.
c. A star is being formed.
d. A planet has collided with a star.

(6) Which stars can become black holes?
a. All stars; a small one forms in their core, and then grows.
b. Only small stars; the big ones are blown away by supernova explosions.
c. Very massive stars; smaller ones become white dwarfs or neutron stars.
d. Stars which get too close to other black holes turn into new black holes.

(7) What is an open cluster?
a. A group of similar stars that is spread over more than one constellation.
b. A large group of many thousands of stars, usually old, in our galaxy's halo.
c. A small group of stars, usually young, blue and bright, in our galaxy's disk.
d. A globular cluster which has been torn apart by a collision with another one.

(8) What do all main sequence stars have in common?
a. They have not yet started producing nuclear reactions.
b. They are at the stage of burning hydrogen in their cores.
c. They have already finished burning hydrogen in their cores.
d. They are single stars, as opposed to members of a binary system.

(9) Is it correct to view a nova as a new star?
a. Yes, because novas are explosions produced by the first nuclear reactions in a star.
b. Yes, because novas are the collisions of dense clouds that produce newborn stars.
c. No, because novas are just bursts of nuclear fusion on the surface of white dwarfs.
d. No, because novas are flashes produced by stars disappearing down black holes.

(10) Are there globular clusters in our galaxy?
a. Yes, there is one near the center of the galaxy.
b. Yes, we know more than 100, scattered in the halo of the galaxy.
c. Yes, there are hundreds of thousands of them in the galactic disk.
d. No, globular clusters are seen only in distant galaxies.

(11) What is the Crab nebula?
a. A supernova remnant.
b. A planetary nebula.
c. A molecular cloud.
d. A nearby galaxy.

(12) What is at the center of the Crab nebula?
a. A white dwarf.
b. A brown dwarf.
c. A black hole.
d. A neutron star.

(13) When can a collapsed cloud fragment be called a star?
a. When the temperature on its surface is more than 10 million degrees.
b. When the temperature in the core is more than 100,000 degrees.
c. When nuclear fusion reactions start occurring in its center.
d. When we can see it with our telescopes.

(14) What keeps white dwarfs from continuously shrinking to smaller sizes?
a. The resistance of electrons in them to being squeezed together.
b. The energy produced by nuclear reactions in their cores.
c. They are so cold that they become solid as opposed to gaseous.
d. The gravitational pull from other nearby stars.

(15) Which of these is a possible cause for a supernova?
a. The formation of a bright young star out of interstellar matter.
b. The explosion at the end of a very massive star's life.
c. The formation of a new galaxy out of intergalactic matter.
d. The expansion of a small star to supergiant size at the end of its life.

(16) What evidence do we have that light is attracted by gravity?
a. The fact that Einstein predicted it as a consequence of his theories.
b. We don't have real evidence yet, it is a theoretical prediction.
c. The fact that light cannot go through thick clouds of gas and dust.
d. The bending and lensing of light by very massive objects.

(17) Which star clusters are usually older, in our galaxy?
a. Open clusters, which have opened up and lost stars over time.
b. Globular clusters, which are all at least 10 billion years old.
c. They are equally old, but open clusters just happen to be smaller.
d. There is no general pattern, both types can be either young or old.

(18) Why can't neutron stars be more massive than about 3 solar masses?
a. Because the heavier stars that would form them have not exploded yet.
b. Because even the heaviest stars only leave behind a core of 3 solar masses.
c. Because the ones that would be heavier collapse to form black holes instead.
d. Because there are no stars whose mass is more than 3 solar masses.

(19) Which of the following things do you see when looking at an eclipsing binary star system?
a. A two-star system in which both stars can be seen.
b. A star from which the amount of light we receive changes in time.
c. One for which the frequency of the spectral lines changes in time.
d. One whose visible spectrum shows both emission and absorption lines.

(20) Would you be able to land on the surface of a black hole?
a. No, there is no hard surface to stand on, you would just fall inward.
b. No, because black holes spin so fast you would be thrown outward.
c. Yes, but you would be permanently stuck on the black hole's surface.
d. For a moment, but then you would be flattened by its strong gravity.

(21) How far are we from the Sun, approximately?
a. 1,500 km.
b. 150 million km.
c. 1,500 light years.
d. 150 million light years.

(22) Which property of a planet or star cannot be measured unless we observe something orbiting around it?
a. Radius.
b. Mass.
c. Distance.
d. Temperature.

(23) Which of the following makes it more likely that a given interstellar cloud will start forming stars within it?
a. The cloud is cold.
b. The cloud is hot.
c. The cloud is spinning fast.
d. The cloud is outside the disk of our galaxy.

(24) For which stars can we use the parallax method to find their distance?
a. The ones for which we can obtain a good spectrum.
b. All stars that we can see with our telescopes.
c. The nearest ones, out to several hundred light years.
d. The brighter ones, up to apparent magnitude 2.

(25) Which of these stars is nearest to us?
a. Sirius.
b. Alpha Centauri.
c. Polaris.
d. Barnard's star.

(26) What is a brown dwarf?
a. A white dwarf surrounded by a cloud which prevents us from seeing it.
b. A planet that is not attached to a star but moves freely in space.
c. A would-be star that didn't have enough mass to start burning hydrogen.
d. A white dwarf that has cooled down and does not glow so bright.

(27) How do we measure a star's proper motion?
a. From its distance and luminosity.
b. From its position on the HR diagram.
c. From the redshift or blueshift of its spectral lines.
d. From the visible motion of the star across the sky over long times.

(28) Can we tell how large a star is from its size on a photograph?
a. No, almost always a large image only means that the star is very bright.
b. Yes, we just need to magnify the photograph and use a ruler.
c. Yes, but we have to take into account how far the star is.
d. No, because all stars produce images of the same size.

(29) Which one is hotter, a B5 star or a K5 star?
a. The K5 star.
b. The B5 star.
c. They have the same temperature.
d. It could be either one, we need more information to answer this question.

(30) Which is hotter, a supergiant star or a main sequence star?
a. The supergiant star.
b. The main sequence star.
c. They have the same temperature.
d. It could be either one, we need more information to answer this question.

Short-Answer Questions

(31) Do less massive or more massive stars live longer? Explain your answer briefly.

(32) Name two stages that the Sun will go through after the current one, including what it will become at the end.

(33) What is a black hole?

(34) Where do we find the most massive black holes we know?

(35) What can you do to find out how hot a star is?