question

Where does an object on an elliptical orbit experience the greatest acceleration?

answer

where spacetime has the most curvature

question

Imagine that the Sun could be turned into a black hole without changing its mass. How would Earth's orbit change?

answer

Earth's orbit would not change.

question

Imagine that the Sun gained mass without changing its radius. How would the structure of spacetime change at the distance of Earth's orbit?

answer

Spacetime would become more curved at Earth's orbit.

question

From the viewpoint of an observer in the orbiting rocket, what happens to time on the other rocket as it falls toward the event horizon of the black hole?

answer

Time runs increasingly slower as the rocket approaches the black hole.

question

As the falling rocket plunges toward the event horizon, an observer in the orbiting rocket would see that the falling rocket __________.

answer

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

question

From Part B, you know that from afar we'll never see the in-falling rocket cross the event horizon, yet it will still eventually disappear from view. Why?

answer

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

question

If you were inside the rocket that falls toward the event horizon, you would notice your own clock to be running __________.

answer

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

question

If you were inside the rocket that falls toward the event horizon, from your own viewpoint you would __________.

answer

accelerate as you fall and cross the event horizon completely unhindered

question

All millisecond pulsars are now, or once were, members of binary-star systems.

answer

True

question

The fact that gamma-ray bursts are so distant means that they must be very energetic events.

answer

True

question

All things, except light, are attracted by gravity.

answer

False

question

According to general relativity, space is warped, or curved, by matter.

answer

True

question

Although visible light cannot escape from a black hole, high-energy radiation, like gamma rays, can escape.

answer

False

question

A neutron star is about the same size as

answer

A U.S. city

question

Thousands of black holes have now been identified in our Galaxy.

answer

False

question

The most rapidly "blinking" pulsars are those that

answer

spin fastest

question

The X-ray emission from a neutron star in a binary system comes mainly from

answer

heated material in an accretion disk around the neutron star.

question

Gamma-ray bursts are observed to occur

answer

approximately uniformly over the entire sky.

question

If the Sun were magically to turn into a black hole of the same mass,

answer

Earth's orbit would remain unchanged.

question

The best place to search for black holes is in a region of space that

answer

has strong X-ray emission.

question

In a neutron star, the core is

answer

made of compressed neutrons in contact with each other.

question

Two important properties of young neutron stars are

answer

extremely rapid rotation and a strong magnetic field.

question

An object more massive than the Sun, but roughly the size of a city, is a

answer

neutron star

question

The mass range for neutron stars is

answer

1.4 to 3 solar masses

question

Neutron stars have

answer

very strong bi-polar magnetic fields.

question

In the Lighthouse Model,

answer

if the beam sweeps across us, we will detect a pulse of radiation.

question

Neutron stars do not have

answer

rotation periods comparable to the Sun's.

question

The supernova of 1054 AD produced:

answer

a pulsar with a period of 33 milliseconds, visible optically.

question

Three terrestrial-sized planets in orbits of a fraction of an AU have been found near

answer

a millisecond pulsar.

question

Almost half of all known millisecond pulsars are found in what type of object?

answer

globular clusters

question

X-ray bursters occur in binary star systems. The two types of stars that must be present to make up such an object are:

answer

a main sequence or giant star and a neutron star in a mass transfer binary.

question

Pulsars have a measured mass of

answer

about 1.4 solar masses.

question

You would expect millisecond pulsars to be

answer

part of a binary system.

question

A proposed explanation for gamma-ray bursters is A-coalescence of a neutron star binary. B-hypernova-making black holes and bi-polar jets. C-collisions between two white dwarfs. Both A and B are possible. All three are possible.

answer

Both A and B are possible.

question

What would happen if more mass was added to a 1.4 solar mass neutron star?

answer

It could eventually become a black hole, via a hypernova explosion.

question

A hypernova creates

answer

A black hole

question

The densely packed neutrons of a neutron star cannot balance the inward pull of gravity if the total mass is

answer

greater than Schwartzschild's limit of 3 solar masses.

question

The Schwartzschild radius for a 12 solar mass star is

answer

36 km

question

What explanation does general relativity provide for gravity?

answer

Gravity is the result of curved spacetime.

question

An observer on a planet sees a spaceship approaching at 0.5c. A beam of light projected by the ship would be measured by this observer to travel at

answer

c.

question

As a spaceship's velocity gets closer to the speed of light

answer

its length will decrease and its clock will run more slowly.

question

If light from a distant star passes close to a massive body, the light beam will

answer

bend towards the star due to gravity.

question

What can we detect from matter that has crossed an event horizon?

answer

Nothing

question

As a spaceship nears an event horizon, a clock on the spaceship will be observed

answer

to run slowly

question

If the Sun were replaced by a one solar mass black hole

answer

we would still orbit it in a period of one year.

question

What is Cygnus X-1?

answer

the leading candidate for an observable black hole binary system

question

A method for identifying a black hole is to

answer

look for their effects on nearby companions.

question

The largest known black holes

answer

lie in the cores of the most massive galaxies.

question

Any main sequence star over 25 solar masses will probably retain enough matter in its core after its type II supernova to make a black hole.

answer

True

question

The Schwarzschild radius of a black hole is about 3 km per solar mass; it is amazingly linear over a wide range of masses.

answer

True

question

Special relativity says that c, the speed of light, is the maximum velocity for both matter and energy in our universe.

answer

True

question

Who discovered the first four pulsars?

answer

Jocelyn Bell

question

In a neutron star, the protons and electrons are fused together, leaving only neutrons.

answer

True

question

A neutron star is what remains after a Type II supernova explosion has destroyed the rest of the star.

answer

True

question

In a neutron star, the electrons in the core are all in contact with each other.

answer

False

question

The "pulse" from a pulsar is due to the rapidly expanding and contracting outer shell of the star.

answer

False

question

Pulsars are created in a Type I supernova.

answer

False

question

The pulses from a pulsar are most likely coming from localized areas near the magnetic poles.

answer

True

question

While most pulsars slow down over time, millisecond pulsars spin faster due to the mass transfer from a close companion.

answer

True

question

An X-ray burster is similar to a nova.

answer

True

question

Gamma-ray bursts are all found to be within our galaxy.

answer

False

question

Gamma-ray bursters seem scattered randomly over the entire sky.

answer

True

question

All the gamma-ray bursters measured to date have distances of millions or even billions of light years.

answer

True

question

All Type II supernovae produce neutrons stars when they collapse.

answer

False

question

Both space and time are warped near the strong gravitational fields of neutron stars and black holes.

answer

True

question

No communication is possible across an event horizon.

answer

True

question

The presently known laws of physics clearly describe the conditions inside a black hole's event horizon.

answer

False

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