Suppose an object radiates in the visible range of light. We also see steady pulses of intense radio and visible light with a time interval of 0.15 seconds between pulses. Occasionally we detect powerful bursts of X-rays from the object. Choose the best theory.
a. A pulsar with an accretion disk from a visible star, and the orbit plane is oriented so that we see no eclipsing.
b. A supermassive black hole.
c. A black hole-visible star binary pair with short orbital period.
d. A quasar at the center of interacting galaxies, which in turn are orbiting each other very quickly.
If our solar system were half-way from the center to the edge of a giant elliptical galaxy, how would our night sky look different?
a. We would see a much wider band of hazy light like the “milky way” and we would see a lot fewer stars.
b. We would see pretty much the same kind of night sky as we see now.
c. We would see no hazy “milky way” arcing across the sky, but we would see more stars overall, and very few or no dust clouds at all.
d. We would see no hazy band of “milky way” and we would see dust clouds all around the sky, with fewer stars.
Where did the most abundant elements in the Universe come from?
a. Gamma rays produced protons and all the other elements in the big bang.
b. Gamma rays produced protons and neutrons in the big bang; protons and neutrons formed helium during the next few minutes; fusion in stars produced all other elements.
c. Gamma rays produced protons and helium in the big bang; fusion during the first three minutes produced oxygen; stars produced the all other elements.
d. Gamma rays produced protons, helium, and carbon nuclei in the big bang; nuclear fusion in stars produced all other elements.
Why do astronomers say that our galaxy has a supermassive black hole in its core?
a. Emissions at galactic center include energetic lightray bursts, and the known mechanism for this kind of energy is from a supermassive blackhole.
b. We can view conditions in other galaxies, and all of them exhibit behavior that we can only explain with a supermassive blackhole.
c. Stars are orbiting with speeds so high that only a supermassive blackhole can cause the observed speeds.
d. Long wavelength observations show gas clouds orbiting at high speed, the only credible mechanism that explains this behavior is a supermassive blackhole.
Why do metal-poor stars in our galaxy tend to have large elliptical orbits outside the disk?
a. Because of a possible past interaction between our galaxy and a neighboring galaxy changed the circular orbits of these early stars into elliptical orbits.
b. Because these stars formed before the spiral shape formed, when the galaxy was a larger, more diffuse cloud, with no well-defined concentration of mass near the center.
c. Because metals, with higher gravitational attraction, tend to stabilize stellar orbits.
d. They don’t have this tendency. The metal-poor stars exhibit well-organized orbits around galactic center, with nearly circular orbits.
Which of these statements regarding the stimulation of star birth is the most nonsensical claim.
a. Exploding stars in regions of gas/dust clouds can stimulate star formation.
b. Interactions or mergers of galaxies compress gas/dust clouds and stimulate star formation.
c. In spiral galaxies, stars form rapidly after gas/dust clouds leave the spiral arms and become less compressed.
d. In the early Universe star formation was more rapid than now because of the overall crowded conditions.
Cosmologists refer to “the decoupling event.” What do they mean by that?
a. The time when radiation had cooled enough to allow neutral atoms to form.
b. The time when protons and neutrons first formed.
c. The formation of the first stars prior to the formation of galaxies.
d. The rapid expansion of space just after the first fraction of a second of the Big Bang.
Suppose you observe a main-sequence 2 solar mass star orbiting an 8 solar mass object too dim to detect. What is the most likely identity of the dim object?
a. The object is probably a neutron star.
b. The object is probably a black hole.
c. The object is probably a brown dwarf.
d. The object is probably a white dwarf.
Suppose a collapsing interstellar gas cloud had a composition almost entirely of helium and a few percent heavier elements, but no hydrogen.
a. Before the central temperature could reach the threshold for nuclear fusion, the object would form a black hole.
b. Formation of a star would be impossible, because the central temperature would never be high enough for fusion to occur.
c. A planet-like object would form in all cases, regardless of the mass of the cloud.
d. If the mass is sufficient, a star could form but would take longer than normal because 100 million Kelvins would take longer to achieve.
What differences would we expect to observe on the Sun if it did NOT rotate differentially?
a. It would exhibit violent surface activity continually, including flares and sunspots.
b. X-ray images of the Sun would show more intense X-ray emission than it does now.
c. The corona would be much hotter than it is now.
d. It would exhibit very little surface activity, and there would be no sunspot cycles.
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