Chapter 14

A typical white dwarf is _________. about the same size and mass as the Sun but much hotter as large in diameter as the Sun but only about as massive as Earth as massive as the Sun but only about as large in size as Jupiter as massive as the Sun but only about as large in size as Earth

The maximum mass of a white dwarf is _________. about 3 times the mass of our Sun about 1.4 times the mass of our Sun limitless; there is no theoretical limit to the maximum mass of a white dwarf about the mass of our Sun

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 collapse in size, becoming a neutron star. The white dwarf will collapse to become a black hole. The white dwarf will undergo a nova explosion. The white dwarf will explode completely as a white dwarf supernova.

Which of these objects has the smallest radius? a 1.2MSun white dwarf a 0.6MSun white dwarf Jupiter

If we see a nova, we know that we are observing a rapidly rotating neutron star. a gamma ray-emitting supernova. a white dwarf in a binary system.

According to our modern understanding, what is a nova? the explosion of a massive star at the end of its life a rapidly spinning neutron star the sudden formation of a new star in the sky an explosion on the surface of a white dwarf in a close binary system

After a massive-star supernova, what is left behind? always a white dwarf always a black hole always a neutron star either a white dwarf or a neutron star either a neutron star or a black hole

What is the ultimate fate of an isolated white dwarf? It will cool down and become a cold black dwarf. The electron degeneracy pressure slowly overwhelms gravity and the white dwarf evaporates. As gravity overwhelms the electron degeneracy pressure, it will explode as a nova. As gravity overwhelms the electron degeneracy pressure, it will explode as a supernova. As gravity overwhelms the electron degeneracy pressure, it will become a neutron star.

Which of the following best describes what would happen if a 1.5 solar mass neutron star, with a diameter of a few kilometers, were suddenly to appear in your hometown? The entire mass of the Earth would end up as a thin layer, about 1 cm thick, over the surface of the neutron star. It would rapidly sink to the center of the Earth. It would crash into the Earth, throwing vast amounts of dust into the atmosphere which in turn would cool the Earth. Such a scenario is probably what caused the extinction of the dinosaurs. The combined mass of the Earth and the neutron star would cause the neutron star to collapse into a black hole. It would crash through the Earth, creating a large crater, and exit the Earth on the other side.

A typical neutron star is more massive than our Sun and about the size (radius) of _________. a small asteroid (10 km in diameter) Jupiter Earth the Moon

Pulsars are thought to be _________. unstable high-mass stars accreting black holes rapidly rotating neutron stars accreting white dwarfs

How is an X-ray burst (in an X-ray binary system) similar to a nova? Both involve explosions on the surface of a stellar corpse. Both typically recur every few hours to every few days. Both are thought to involve fusion of hydrogen into helium. Both result in the complete destruction of their host stars.

Which of the following statements about electron degeneracy pressure and neutron degeneracy pressure is true? In a black hole, the pressure coming from neutron degeneracy pressure is slightly greater than that coming from electron degeneracy pressure. Both electron degeneracy pressure and neutron degeneracy pressure help govern the internal structure of a main-sequence star. The life of a white dwarf is an ongoing battle between electron degeneracy pressure and neutron degeneracy pressure. Electron degeneracy pressure is the main source of pressure in white dwarfs, while neutron degeneracy pressure is the main source of pressure in neutron stars.

Which of these isolated neutron stars must have had a binary companion? a pulsar inside a supernova remnant that pulses 30 times per second an isolated pulsar that pulses 600 times per second a neutron star that does not pulse at all

What do we mean by the event horizon of a black hole? It is the distance from the black hole at which stable orbits are possible. It is the very center of the black hole. It is the point beyond which neither light nor anything else can escape. It is the place where X rays are emitted from black holes

Imagine that our Sun were magically and suddenly replaced by a black hole of the same mass (1 solar mass). What would happen to Earth in its orbit? Earth would almost instantly be sucked into oblivion in the black hole. Earth would orbit faster, but at the same distance. Earth would slowly spiral inward until it settled into an orbit about the size of Mercury's current orbit. Nothing—Earth's orbit would remain the same.

What makes us think that the star system Cygnus X-1 contains a black hole? It emits X rays characteristic of an accretion disk, but the unseen star in the system is too massive to be a neutron star. No light is emitted from this star system, so it must contain a black hole. The fact that we see strong X-ray emission tells us that the system must contain a black hole. Cygnus X-1 is a powerful X-ray burster, so it must contain a black hole.

The Schwarzschild radius of a black hole depends on ________. only the mass of the black hole both the mass and chemical composition of the black hole the observationally measured radius of the black hole the way in which the black hole formed

If your spaceship flew within a few thousand kilometers above the event horizon, you and your ship would be rapidly sucked into it. This statement makes sense. Due to high gravitational force the ship will be sucked straight into the black hole without any revolutions around it regardless of the movement and any possible orbital corrections of the spaceship. This statement does not make sense. A circular orbit, even at a distance of a few thousand kilometers above the event horizon is perfectly stable. If you use the engines of the spaceship to put it on such orbit, the spaceship will not be sucked into the black hole.

From your point of view, an object falling toward a black hole will never cross the event horizon. This statement makes sense. According to Einstein's theory, from your point of view, the object takes forever to cross the event horizon. You'll see how the object vanishes from view due to the huge gravitational red-shift of light. This statement does not make sense. The event horizon is a mathematical boundary, not a physical one, so the object will cross it. No theory can forbid you to actually see the moment of crossing the event horizon by the object.

The best way to search for black holes is to look for small black circles in the sky. This statement makes sense. The black holes do not emit or reflect light, therefore they appear as noticeable black circles on the background of stars in the sky. This statement does not make sense. We cannot distinguish between the objects that do not emit or reflect light and their black background using direct observations. However, the presence of the objects can be deduced from the indirect observations.

Which of these objects has the largest radius? a 1.2MSun white dwarf a 1.5MSun neutron star a 3.0MSun black hole

What would happen if the Sun suddenly became a black hole without changing its mass? The black hole would quickly suck in the Earth. Earth would gradually spiral into the black hole. Earth's orbit would not change.

Where do gamma-ray bursts tend to come from? neutron stars in our galaxy black holes in our galaxy extremely distant galaxies

Based on current evidence, which of the following statements about gamma ray bursts is true? They come primarily from the Milky Way's central black hole. All gamma ray bursts are produced by supernovae. They occur in the same types of close binary systems that produce X-ray bursts. All those that we have detected occurred in distant galaxies.

The more massive a white dwarf, the ________. higher its luminosity larger its radius higher its temperature smaller its radius

You want to determine whether a mystery object is a neutron star or a white dwarf. Which of the following properties would demonstrate that it is definitely a neutron star? You want to determine whether a mystery object is a neutron star or a white dwarf. Which of the following properties would demonstrate that it is definitely a neutron star? Every decade or so, it erupts in a nova explosion. It dims and brightens more than twice per second. It is surrounded by a planetary nebula. It emits most strongly in visible and ultraviolet light.

If you were to come back to our Solar System in 6 billion years, what might you expect to find? a red giant star a black hole a rapidly spinning pulsar a white dwarf Everything will be essentially the same as it is now.

Which stars are more common? Which stars are more common? White dwarfs and neutron stars are about equally common. Neutron stars and black holes are about equally common. black holes neutron stars white dwarfs

The Crab Pulsar is pulsing in visible light 30 times per second. Why? It's a mystery; no one really knows. A jet ejects energy and particles from a hot spot 30 times per second. It rotates 30 times per second. It is eclipsed by a companion 30 times per second.

Order the following objects in increasing size (radius): Order the following objects in increasing size (radius): Jupiter, white dwarf, Sun, neutron star neutron star, Jupiter, white dwarf, Sun Jupiter, white dwarf, neutron star, Sun neutron star, white dwarf, Jupiter, Sun