Astronomy - Chapter 14

Match words at the left to the correct blanks in the sentences at right. Not all words will be used

- A(n) "accretion disk" can form around a white dwarf, neutron star, or black hole in a binary system. -A neutron star can remain stable in size because of "neutron degeneracy pressure" -The "event horizon" marks the boundary between the inside and outside of a black hole. -The "singularity" is the place to which all of a black hole's mass is in principle located within the black hole. -A(n) "nova" occurs when fusion ignites on the surface of a white dwarf. -A(n) "pulsar" is rapidly rotating neutron star. -A white dwarf can remain stable in size because of "electron degeneracy pressure." -The radius of a white dwarf is determined by a balance between the inward force of gravity and the outward push of "electron degeneracy pressure."

Which of the following accurately describe some aspect of gravitational waves? 1. Gravitational waves are predicted to travel through space at the speed of light. 2. Gravitational waves carry energy away from their sources of emission. 3. Gravitational waves come from funnel-shaped regions of the universe. 4. The existence of gravitational waves is predicted by Newton's universal law of gravitation. 5. The existence of gravitational waves is predicted by Einstein's general theory of relativity. 6. Gravitational waves are an extremely low-energy form of light. 7. The first direct detection of gravitational waves came in 2015.

1, 2, 5, 7

If you tried to fly into a ___________, you would be killed by tidal forces before you crossed the event horizon.

10-solar-mass black hole

Part complete What is the Schwarzschild radius of a 10 solar mass black hole? 1 billion km 3 billion km 30 km 10 km 30 billion km

30 km

Which of the following best describes a black hole? A funnel-shaped, bottomless pit in the universe. An object that sucks in all the light from stars that are near it. A place from which the escape velocity exceeds the speed of light. An object that is completely black in color.

A place from which the escape velocity exceeds the speed of light.

Which statement about pulsars is true? All pulsars are neutron stars, but not all neutron stars are pulsars. All neutron stars are pulsars. Pulsars can "pulse" no more than about once a day. Pulsars can form only in close binary systems.

All pulsars are neutron stars, but not all neutron stars are pulsars.

Consider the statement from Part A reading "a 3-solar-mass black hole may be hidden between Jupiter and Saturn." How do we know this statement is not true? An object of that mass would disrupt the orbits of the planets in our solar system. The black hole would occassionallly eclipse Saturn, but we never see such eclipses. Black holes must have more than 3 solar masses. We would have by now detected it with X-ray telescopes.

An object of that mass would disrupt the orbits of the planets in our solar system.

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.

Earth's orbit would not change.

Which of the following statements about electron degeneracy pressure and neutron degeneracy pressure is true? Both electron degeneracy pressure and neutron degeneracy pressure help govern the internal structure of a main-sequence star. In a black hole, the pressure coming from neutron degeneracy pressure is slightly greater than that coming from electron degeneracy pressure. 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.

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

Consider the statement from Part A reading "the singularity of a black hole has infinite density." Why is this statement in the "unknown" bin? We have not yet detected gravitational waves from a singularity. We have not yet detected X-ray emissions from a singularity. The idea of singularlity is inconsistent with Newton's universal law of gravitation. General relativity and quantum mechanics give different answers about the nature of singularity.

General relativity and quantum mechanics give different answers about the nature of singularity.

What do we mean by the event horizon of a black hole? It is the very center of the black hole. It is the distance from the black hole at which stable orbits are possible. 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.

It is the point beyond which neither light nor anything else can escape.

Consider a binary system of two neutron stars. How should the emission of gravitational waves affect this system? It should cause the orbits of the two objects to grow larger with time. It should cause the orbits of the two objects to decay with time. It should cause the two objects to lose mass with time. It should cause the two objects to gain mass with time.

It should cause the orbits of the two objects to decay with time.

From Part B, you know that from afar you'll never see the in-falling rocket cross the event horizon, yet it will still eventually disappear from view. Why? Even though you won't see it cross the event horizon, it does cross it, and that means you can no longer see it. Its light will become so redshifted that it will be undetectable. The black hole's blackness will drown out the light of the rocket. Tidal forces will squeeze the in-falling rocket to an undetectably thin line.

Its light will become so redshifted that it will be undetectable.

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. Nothing—Earth's orbit would remain the same. Earth would slowly spiral inward until it settled into an orbit about the size of Mercury's current orbit. Earth would orbit faster, but at the same distance.

Nothing—Earth's orbit would remain the same.

Gravitational waves were first detected directly in 2015. According to models, the source of these gravitational waves was

The merger of two black holes

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

The white dwarf will explode completely as a white dwarf supernova.

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.

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.

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.

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.

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.

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.

Part complete Consider the statement from Part A reading "black holes make up 1% of the mass of the Milky Way Galaxy." Why is this statement in the "unknown" bin? According to our understanding of stellar evolution, black holes should make up a much lower percentage of the galaxy's mass. We do not know the mass of the Milky Way's central black hole. According to our understanding of stellar evolution, black holes should make up a much higher percentage of the galaxy's mass. We cannot detect all black holes and therefore don't know the percentage of the galaxy's mass they make up.

We cannot detect all black holes and therefore don't know the percentage of the galaxy's mass they make up.

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

a 1.2 MSun white dwarf

A pulsar is ____ an unstable high-mass star. a rapidly rotating neutron star. an accreting white dwarf.

a rapidly rotating neutron star.

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

a small asteroid (10 km in diameter)

If you were inside the rocket that falls toward the event horizon, from your own viewpoint you would __________. slow down and come to a stop at the event horizon slow down and cross the event horizon at low speed accelerate as you fall and cross the event horizon completely unhindered

accelerate as you fall and cross the event horizon completely unhindered

A(n) ______ consists of hot, swirling gas captured by a white dwarf (or neutron star or black hole) from a binary companion star.

accretion disk

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

an explosion on the surface of a white dwarf in a close binary system

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

as massive as the Sun but only about as large in size as Earth

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

as massive as the Sun but only about as large in size as Earth

If you were inside the rocket that falls toward the event horizon, you would notice your own clock to be running __________. increasingly faster as you approach the event horizon at a constant, normal rate as you approach the event horizon increasingly slower as you approach the event horizon

at a constant, normal rate as you approach the event horizon

If you tried to visit a _________________, you would probably be killed by radiation well before you reached the black hole itself.

black hole in an X-ray binary system

LIGO detects gravitational waves because the lengths of its arms change as gravitational waves pass by. About how much are these lengths expected to change when LIGO detects gravitational waves from the merger of two neutron stars or two black holes? by about the size of an atom by about 1 meter by about 0.1% of the arm's length by an amount smaller than the diameter of a proton

by an amount smaller than the diameter of a proton

Given such small length changes (as noted in Part D), what can give scientists confidence that they have really detected a gravitational wave signal? detecting the same changes at more than one location observing the gravitational wave event with a visible-light telescope that can actually see two objects merge detecting the same changes repeatedly, each several minutes apart checking all wiring really carefully to be sure there are no errors in the measurements

detecting the same changes at more than one location

The radius of a white dwarf is determined by a balance between the inward force of gravity and the outward push of _______

electron degeneracy pressure

Part complete The boundary from within which light cannot escape from a black hole is called the black hole's __________. singularity Schwarzschild radius event horizon spacetime distortion zone

event horizon

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

extremely distant galaxies

A(n) ______ occurs when fusion creates iron in the core of a star.

massive star supernova

A(n) _____ occurs when hydrogen fusion ignites on the surface of a white dwarf in a binary system.

nova

With current technology, we expect to be able to detect (directly) gravitational waves from a binary system of two neutron stars or two black holes __________. only from the times when the objects first formed from the supernovas of the stars that produced them from any time during which the two objects orbit each other from a few days after the two objects merge, when the merged object suddenly explodes only from the instant when the two objects merge into one

only from the instant when the two objects merge into one

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

rapidly rotating neutron stars

As the falling rocket plunges toward the event horizon, an observer in the orbiting rocket would see that the falling rocket __________. slows down as it approaches the event horizon and never actually crosses the event horizon slows down near the event horizon so that it crosses the event horizon at a low speed moves at constant speed as it approaches and crosses the event horizon accelerates as it falls and crosses the event horizon at high speed

slows down as it approaches the event horizon and never actually crosses the event horizon

Degeneracy pressure arises when ________. the temperature reaches a critically high value a star's core is producing less energy than the star is radiating away from its surface the speeds of subatomic particles reach the speed of light an object becomes as small or smaller than Earth subatomic particles are packed as tightly as the laws of quantum mechanics allow

subatomic particles are packed as tightly as the laws of quantum mechanics allow

Ignoring any radiation, you could in principle survive the journey across the event horizon of a ___________________

supermassive black hole.

2. A white dwarf in a close binary system will explode as a supernova if it gains enough mass to exceed the _____________

white dwarf limit (1.4 solar masses).

A(n) _______ can occur only in a binary system, and all such events are thought to have about the same luminosity.

white dwarf supernova