Question 1

A black hole is so named because

Accepted Answer

A)   the gravitational field is so high that the wavelength of its emitted light is gravitationally redshifted to radio wavelengths.
B)   it emits no visible light because it is so cold, less than 100 K.
C)   no light can escape from it due to its powerful gravitational field.
D)   it is colder than the rest of the universe; that is, its effective temperature is less than 3 K.

Question 2

Which of these statements is NOT an observation confirming the predictions of general relativity?

Accepted Answer

A)   Light is deflected in the curved space near the Sun.
B)   The perihelion of the orbit of Mercury shifts more than the amount predicted by Newtonian physics.
C)   Primordial black holes have been detected.
D)   The spectra of stars exhibit the gravitational redshift.

Question 3

Which of these objects is NOT an end point of a star's evolutionary life?

Accepted Answer

A)   red giant
B)   supernova
C)   black hole
D)   neutron star A

Question 4

What is located in the exact center of a Kerr (rotating)  black hole?

Accepted Answer

A)   nothing
B)   the singularity
C)   the event horizon
D)   the ergoregion A

Question 5

Suppose an astronaut is far from a planet with a very strong gravitational field. The astronaut is also watching a clock on the surface of this planet. During the time in which his own clock ticks out a time of 1 hour, how much time does the clock on the planet tick out?

Accepted Answer

A)   less than 1 hour (but more than zero) 
B)   no time at all
C)   more than 1 hour
D)   exactly 1 hour, the same as the astronaut's clock

Question 6

Suppose an observer sees a spaceship with a clock on it hurtling past them at 80% of the speed of light. As it goes by, the second hand on the ship's clock ticks off 5 seconds. How much time elapsed on the observer's clock during this occurrence?

Accepted Answer

A)   more than 5 seconds if the spaceship is approaching the observer and less than 5 seconds if it is moving away from the observer
B)   less than 5 seconds
C)   more than 5 seconds
D)   5 seconds-the same as on the ship's clock

Question 7

In a binary star system, one component is found to have about 3 solar masses, the other about 7 solar masses. The 3-solar-mass star is visible from Earth, but the 7-solar-mass star is not. Theoretical considerations declare that the 7-solar-mass star must be a

Accepted Answer

A)   neutron star.
B)   cool planetary object.
C)   white dwarf.
D)   black hole.

Question 8

Gas jets have often formed perpendicular to the plane of the accretion disk around a black hole or a neutron star. What propels the gas away from the hole or star?

Accepted Answer

A)   magnetic forces from the object's strong magnetic field
B)   conservation of momentum since the outgoing particles are pair-produced as virtual particles near the object
C)   enormous pressure of the compressed infalling gas of the accretion disk
D)   strong curvature of spacetime near the object

Question 9

What would the mass of a primordial black hole need to have been for it to be just disappearing now due to the loss of Hawking radiation?

Accepted Answer

A)   10 kg
B)   10 million kg
C)   10,000 kg
D)   10 billion kg

Question 10

Sometimes particle-antiparticle pairs are created and then annihilate so quickly that observers cannot know that they ever existed. What are these particles (or antiparticles)  called?

Accepted Answer

A)   relativistic particles
B)   temporary particles
C)   field particles
D)   virtual particles

Question 11

How has the diameter of the black hole candidate Cygnus X-1 been estimated?

Accepted Answer

A)   from the angular size in the sky of Cygnus X-1 and its known distance from Earth
B)   from the time scale of the flickering of the X-rays Cygnus X-1 emits
C)   from the orbital period around a companion star of Cygnus X-1
D)   from the length of time Cygnus X-1 blocks off the light from its companion star when Cygnus X-1 passes in front of (eclipses)  its companion, as seen from Earth

Question 12

One object that is believed to be a black hole in the Milky Way Galaxy is the

Accepted Answer

A)   central star in the Crab Nebula.
B)   central star in the planetary nebula the Ring Nebula in Lyra.
C)   Vela pulsar.
D)   powerful X-ray source Cygnus X-1. D

Question 13

According to Newton's law of gravity, why does Earth orbit the Sun?

Accepted Answer

A)   The Sun exerts a gravitational force on Earth across empty space.
B)   Earth and the Sun are continually exchanging photons of light in a way that holds Earth in orbit.
C)   Matter contains quarks, and Earth and the Sun attract each other with the "color force" between their quarks.
D)   Space around the Sun is curved.

Question 14

What happens to the Schwarzschild radius of a black hole if one doubles the amount of mass in the black hole?

Accepted Answer

A)   The Schwarzschild radius is doubled.
B)   The Schwarzschild radius is halved.
C)   The Schwarzschild radius decreases by a factor of 4.
D)   The Schwarzschild radius is quadrupled (4 times) .

Question 15

The difference between a Schwarzschild black hole (SBH)  and a Kerr black hole (KBH)  is

Accepted Answer

A)   overall mass; an SBH contains about 20 solar masses, whereas a KBH is greater than 20 solar masses.
B)   that the KBH is electrically charged, whereas the SBH is not.
C)   that an SBH is spinning, whereas a KBH is not.
D)   that a KBH is spinning, whereas an SBH is not.

Question 16

Suppose a person is in a jet airliner traveling at a constant speed of 400 km/h in a constant direction. All windows are blocked, so they cannot see outside, and there are no vibrations from the engines. What experiment can be done to determine that they are in fact moving?

Accepted Answer

A)   Suspend a ball by a thread from the ceiling and measure the angle the thread makes with the vertical.
B)   None-all experiments will give the same results that one would get when at rest on the ground.
C)   Measure the speed of a sound wave traveling up the aisle (toward the nose of the aircraft)  and another traveling down toward the tail, and calculate the difference between the two results.
D)   Drop a small rock and measure the distance it moves backward down the aisle as it falls.

Question 17

A scientist is going to make measurements of these entities. For which one will Newtonian physics give answers that are precise enough for practical use?

Accepted Answer

A)   the advance of the perihelion of the orbit of Mercury
B)   the orbit of a satellite around Earth
C)   two neutron stars orbiting each other
D)   GPS locations on Earth from orbiting satellites

Question 18

What name is given to any black hole that might have been created in the Big Bang at the beginning of the universe?

Accepted Answer

A)   supermassive black hole
B)   Schwarzschild black hole
C)   Kerr black hole
D)   primordial black hole

Question 19

Particularly powerful supernovae called "hypernovae" occur in

Accepted Answer

A)   supermassive black holes.
B)   neutron stars.
C)   Wolf-Rayet stars.
D)   hyperspace.

Question 20

What is a virtual particle?

Accepted Answer

A)   particle whose existence is too short for observers to know it ever existed
B)   particle that never does anything wrong
C)   particle that, if it comes in contact with ordinary matter, annihilates to form pure energy
D)   particle, like a photon or a graviton, that is made up of waves

Exam 15: Black Holes: Matters of Gravity

A black hole is so named because

Correct AnswerverifiedShow Answer

Which of these statements is NOT an observation confirming the predictions of general relativity?

Correct AnswerverifiedShow Answer

Which of these objects is NOT an end point of a star's evolutionary life?

Correct AnswerverifiedA

What is located in the exact center of a Kerr (rotating) black hole?

Correct AnswerverifiedA

Suppose an astronaut is far from a planet with a very strong gravitational field. The astronaut is also watching a clock on the surface of this planet. During the time in which his own clock ticks out a time of 1 hour, how much time does the clock on the planet tick out?

Correct AnswerverifiedShow Answer

Suppose an observer sees a spaceship with a clock on it hurtling past them at 80% of the speed of light. As it goes by, the second hand on the ship's clock ticks off 5 seconds. How much time elapsed on the observer's clock during this occurrence?

Correct AnswerverifiedShow Answer

In a binary star system, one component is found to have about 3 solar masses, the other about 7 solar masses. The 3-solar-mass star is visible from Earth, but the 7-solar-mass star is not. Theoretical considerations declare that the 7-solar-mass star must be a

Correct AnswerverifiedShow Answer

Gas jets have often formed perpendicular to the plane of the accretion disk around a black hole or a neutron star. What propels the gas away from the hole or star?

Correct AnswerverifiedShow Answer

What would the mass of a primordial black hole need to have been for it to be just disappearing now due to the loss of Hawking radiation?

Correct AnswerverifiedShow Answer

Sometimes particle-antiparticle pairs are created and then annihilate so quickly that observers cannot know that they ever existed. What are these particles (or antiparticles) called?

Correct AnswerverifiedShow Answer

How has the diameter of the black hole candidate Cygnus X-1 been estimated?

Correct AnswerverifiedShow Answer

One object that is believed to be a black hole in the Milky Way Galaxy is the

Correct AnswerverifiedD

According to Newton's law of gravity, why does Earth orbit the Sun?

Correct AnswerverifiedShow Answer

What happens to the Schwarzschild radius of a black hole if one doubles the amount of mass in the black hole?

Correct AnswerverifiedShow Answer

The difference between a Schwarzschild black hole (SBH) and a Kerr black hole (KBH) is

Correct AnswerverifiedShow Answer

Suppose a person is in a jet airliner traveling at a constant speed of 400 km/h in a constant direction. All windows are blocked, so they cannot see outside, and there are no vibrations from the engines. What experiment can be done to determine that they are in fact moving?

Correct AnswerverifiedShow Answer

A scientist is going to make measurements of these entities. For which one will Newtonian physics give answers that are precise enough for practical use?

Correct AnswerverifiedShow Answer

What name is given to any black hole that might have been created in the Big Bang at the beginning of the universe?

Correct AnswerverifiedShow Answer

Particularly powerful supernovae called "hypernovae" occur in

Correct AnswerverifiedShow Answer

What is a virtual particle?

Correct AnswerverifiedShow Answer

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