PSc 100:
Study Guide Questions for Week 8

1) Long gamma-ray bursts last for typically

a) a few milliseconds.
b) 0.1 - 1 s.
c) 2 - 100 s.
d) a few minutes.
e) 1 hour.

2) Why are GRBs so difficult to study? Pick one or more of the following answers:

I) They are very dim.
II) They occur without "warning" anywhere in the sky.
III) They occur close to the plane of the galaxy, where they are heavily absorbed.
IV) They are dominated by gamma-rays, which have to be observed with satellites.
V) They are difficult to localize because gamma-rays can basically not be focused.

3) Since 1997, astronomers know that GRBs have gradually decaying afterglows in

a) X-rays.
b) visible light.
c) infrared emission.
d) radio waves.
e) All of the above

4) The optical afterglows of GRBs are often found in

a) globular clusters in nearby galaxies.
b) the spiral arms of faint, distant galaxies.
c) the centers of active galaxies.
d) the plane of our Milky Way.
e) supernova remnants in nearby galaxies.

5) If gamma-ray bursts are indeed beamed, then

a) they emit less energy, but there must be more GRB sources
b) they emit more energy, but there must be less GRB sources
c) they emit less energy, and there must be less GRB sources
d) they emit more energy, and there must be more GRB sources
e) they emit the same amount of energy, but there must be more GRB sources

than previously thought, assuming that they emit the same amount of energy in all directions (i.e. emit isotropically).

6) A hypernova is very similar to

a) a nova explosion.
b) a starburst galaxy.
c) the formation process of planetary nebulae.
d) a type II supernova explosion.
e) a type Ia supernova explosion.

7) The neutron-star/black-hole merger model for GRBs would probably only produce

a) nearby GRBs.
b) short GRBs.
c) long GRBs.
d) very bright GRBs.
e) very dim GRBs.

8) The diameter of our Milky Way is approximately

a) 75,000 AU.
b) 100,000 pc.
c) 75,000 LY.
d) 8,500 pc.
e) 85,000 pc.

9) Our sun is located

a) near the center of the Milky Way.
b) in the halo of the Milky Way.
c) at the leading (outer) edge of a spiral arm.
d) in the Galactic bulge.
e) at the trailing (inner) edge of a spiral arm.

10) Which of the following is not a characteristic of the stars of the disk component of our Galaxy?

a) Circular orbits
b) Randomly inclined orbits
c) Higher metal abundance
d) Young stars
e) Located in star formation regions

11) Younger stars have more heavy elements because

a) old stars destroy heavy elements as they age.
b) young stars burn their nuclear fuels faster.
c) heavy elements were made in previous generations of stars.
d) heavy elements haven't had time to settle to the core of these younger stars.
e) All of the above.

12) Choose one or more of the following answers: Population II stars

I) are primarily found in the disk of the galaxy.
II) contain more heavy metals than population I stars.
III) are primarily old low-mass stars.
IV) are located in globular clusters.

13) The distribution of dust in our Galaxy can be traced with observations at

a) radio wavelengths.
b) infrared wavelengths.
c) optical wavelengths.
d) X-rays.
e) gamma-rays.

14) Radio maps of our galaxy show spiral arms because

a) the arms have high Doppler shifts.
b) the gas in the spiral arms is hot enough to emit photons.
c) the dust in spiral arms is denser.
d) the gas in spiral arms is denser.
e) the stars in the spiral arms emit most of their energy at radio wavelengths.

15) Select one or more answers: Star formation in our Milky Way is triggered by

I) shock waves from ionization fronts around O and B stars.
II) shock waves of spiral arms rotating over basically stationary giant molecular clouds.
III) giant molecular clouds passing through basically stationary shock waves of spiral arms.
IV) shock waves from supernova explosions.
V) shock waves from fast pulsar winds.

16) How long does one orbit of the sun around the Milky Way take?

17) Which conclusion could you draw from a rotation curve that corresponds to Keplerian motion?

18) In which of the following wavelength bands can we get the most detailed observations of our Galactic center region?

a) Radio
b) Infrared
c) Optical
d) Ultraviolet
e) Gamma-rays

19) Why is the supermassive black hole in our Galactic center rather unusual compared to other galaxies?

a) It has an extremely high mass of 2.6 million solar masses.
b) It is spinning extremely rapidly.
c) It has a very moderate mass and is unusually faint in X-rays.
d) It has an unusually low mass and is unusually bright in X-rays for its low mass.
e) It does not have an event horizon.

Answers to study guide questions

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