Astr 101-502 Exam 2 Review

Which of the following statements about electron degeneracy pressure and neutron degeneracy pressure is true? (A) 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 (B) In a black hole, the pressure coming from neutron degeneracy pressure is slightly greater than that coming from electron degeneracy pressure (C) The life of a white dwarf is an ongoing battle between electron degeneracy pressure and neutron degeneracy pressure (D) Both electron degeneracy pressure and neutron degeneracy pressure help govern the internal structure of a main-sequence star

(A) 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 the following statements correctly summarize key differences between the disk and the halo? Select all that apply. (A) Gas and dust are abundant in the disk but not in the halo (B) Stars in the disk all orbit in the same direction and nearly the same plane, while halo stars have more randomly oriented orbits (C) Clusters of young stars are found only in the disk (D) Disk stars come in a broad range of masses and colors, while halo stars are mostly of low mass and red

(A) Gas and dust are abundant in the disk but not in the halo, (B) Stars in the disk all orbit in the same direction and nearly the same plane, while halo stars have more randomly oriented orbits, (C) Clusters of young stars are found only in the disk, (D) Disk stars come in a broad range of masses and colors, while halo stars are mostly of low mass and red

What do we mean by the singularity of a black hole? (A) It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions (B) It is the edge of the black hole, where one could leave the observable universe (C) The term is intended to emphasize the fact that an object can become a black hole only once, and a black hole cannot evolve into anything else (D) It is the "point of no return" of the black hole; anything closer than this point will not be able to escape the gravitational force of the black hole

(A) It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions

Which of the following statements about gravitational waves are true? Select all the apply. (A) The emission of gravitational waves from merging black holes is predicted by Einstein's general theory of relativity (B) Scientists seek to detect gravitational waves by using powerful gamma-ray telescopes (C) The emission of gravitational waves from merging black holes is predicted by Newton's universal law of gravitation (D) Two orbiting neutron stars or black holes will gradually spiral toward each other as a result of energy being carried away by gravitational waves (E) The first direct detection of gravitational waves, announced in 2016, came from the LIGO observatory (F) Although gravitational waves are an important theoretical prediction, we do not yet have any observational evidence that they exist

(A) The emission of gravitational waves from merging black holes is predicted by Einstein's general theory of relativity (D) Two orbiting neutron stars or black holes will gradually spiral toward each other as a result of energy being carried away by gravitational waves (E) The first direct detection of gravitational waves, announced in 2016, came from the LIGO observatory

From an observational standpoint, what is a pulsar? (A) an object that emits flashes of light several times per second (or even faster), with near perfect regularity (B) an object that emits random "pulses" of light, sometimes with only a fraction of a second between pulses and other times with several days between pulses (C) a star that slowly changes its brightness, getting dimmer and then brighter, with a period of anywhere from a few hours to a few weeks (D) a star that changes color rapidly, from blue to red and back again

(A) an object that emits flashes of light several times per second (or even faster), with near perfect regularity

What makes up interstellar medium? (A) gas and dust (B) K and M stars (C) open clusters (D) O and B stars (E) all of the above

(A) gas and dust

Where is most of the dark matter in our galaxy thought to exist? (A) spread throughout the halo of the sky (B) in the massive black hole at the galactic center (C) in small, compact objects in the halo of the galaxy (D) spread throughout the disk in the form of neutral hydrogen

(A) spread throughout the halo of the sky

How does an accretion disk around a neutron star differ from an accretion disk around a white dwarf? (A) the accretion disk around a neutron star is much hotter and emits higher-energy radiation (B) the accretion disk around a neutron star always contains much more mass (C) the accretion disk around a neutron star is made mostly of helium while the accretion disk around a white dwarf is made mostly of hydrogen (D) the accretion disk around a neutron star is more likely to give birth to planets

(A) the accretion disk around a neutron star is much hotter and emits higher-energy radiation

What causes the radio pulses of a pulsar? (A) The neutron star undergoes periodic explosions of nuclear fusion that generate radio pulses (B) As the neutron star spins, beams of radio radiation sweep through space. If one of the beams crosses the Earth, we observe a pulse (C) The vibration of the neutron star (D) A black hole near the neutron star absorbs energy and re-emits it as radio waves (E) The neutron star's orbiting companion periodically eclipses the radio waves that the neutron star emits

(B) As the neutron star spins, beams of radio radiation sweep through space. If one of the beams crosses the Earth, we observe a pulse

Which of the following accurately describe some aspect of gravitational waves? Select all that apply. (A) Gravitational waves come from funnel-shaped regions of the universe (B) Gravitational waves are predicted to travel through space at the speed of light (C) The existence of gravitational waves is predicted by Newton's universal law of gravitation (D) The first direct detection of gravitational waves came in 2015 (E) The existence of gravitational waves is predicted by Einstein's general theory of relativity (F) Gravitational waves carry energy away from their sources of emission (G) Gravitational waves are an extremely low-energy form of light

(B) Gravitational waves are predicted to travel through space at the speed of light, (D) The first direct detection of gravitational waves came in 2015, (E) The existence of gravitational waves is predicted by Einstein's general theory of relativity, (F) Gravitational waves carry energy away from their sources of emission

Which of the following statements concerning black hole masses and Schwarzschild radii is not true? (A) The more massive the black hole, the larger the Schwarzschild radius (B) In a binary system with a black hole, the Schwarzschild radius depends on the distance from the black hole to the companion star (C) Even an object as small as you could become a black hole if there were some way to compress you to a size smaller than your Schwarzschild radius (D) For black holes produced in massive star supernovae, Schwarzschild radii are typically a few to a few tens of kilometers

(B) In a binary system with a black hole, the Schwarzschild radius depends on the distance from the black hole to the companion star

How does the interstellar medium affect our view of most of the galaxy? (A) It has no effect on visible-light observations, but prevents us from studying the galactic center with radio waves or X-rays (B) It prevents us from seeing most of the visible and ultraviolet light from the galactic disk (C) It absorbs all wavelengths of light (D) It produces so much visible light that it blocks our view of anything beyond it

(B) It prevents us from seeing most of the visible and ultraviolet light from the galactic disk

If we could view our galaxy from a distance of several hundred thousand light-years, it would appear ____ (A) as a single, bright star (B) as a flattened disk with a central bulge and spiral arms (C) as a faintly glowing band of light stretching all the way around the sky (D) as a faint smudge barely visible to the unaided eye

(B) as a flattened disk with a central bulge and spiral arms

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? (A) by about 1 meter (B) by an amount smaller than the diameter of a proton (C) by about the size of an atom (D) by about 0.1% of the arm's length

(B) by an amount smaller than the diameter of a proton

Consider a binary system of two neutron stars. How should the emission of gravitational waves affect this system? (A) it should cause the two objects to lose mass with time (B) it should cause the orbits of the two objects to decay with time (C) it should cause the two objects to gain mass with time (D) it should cause the orbits of the two objects to grow larger with time

(B) it should cause the orbits of the two objects to decay with time

A 10-solar-mass main-sequence star will produce which of the following remnants? (A) black hole (B) neutron star (C) white dwarf (D) none of the above

(B) neutron star

What caused the rapid spin of a neutron star that we see as a pulsar? (A) the force of the supernova explosion that formed the neutron star (B) the conservation of angular momentum during the collapse of the original star's core (C) the magnetic field that was compressed into the neutron star as it formed (D) astronomers do not know why pulsars spin so rapidly

(B) the conservation of angular momentum during the collapse of the original star's core

Which of the following statements about degeneracy pressure is not true? (A) Degeneracy pressure arises from a quantum mechanical effect that we don't notice in our daily lives (B) Degeneracy pressure can continue to support an object against gravitational collapse even if the object becomes extremely cold (C) Degeneracy pressure can arise only from interactions among electrons (D) Black holes form when gravity overcomes neutron degeneracy pressure

(C) Degeneracy pressure can arise only from interactions among electrons

Suppose you were unfortunate enough to fall into a black hole in a binary system where the black hole was accreting matter from its companion star. Which of the following is most likely to kill you first? (A) the sucking force from the black hole, which will cause your head to explode (B) the crush of gravity at the singularity embedded within the black hole (C) X-rays from the accretion disk (D) tidal forces due to the black hole

(C) X-rays from the accretion disk

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

(C) a place from which the escape velocity exceeds the speed of light

What is the basic definition of a black hole? (A) any object made from dark matter (B) an object that absorbs all light and emits radiation based only on its temperature (C) an object with gravity so strong that not even light can escape (D) a dead star that has faded from view

(C) an object with gravity so strong that not even light can escape

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 ___ (A) from any time during which the two objects orbit each other (B) from a few days after the two objects merge, when the merged object suddenly explodes (C) only from the instant when the two objects merge into one (D) only from the times when the objects first formed from the supernovas of the stars that produced them

(C) only from the instant when the two objects merge into one

Which of the following observatories is most likely to discover a black hole in a binary system? (A) the Hubble Space Telescope (B) the Arecibo Radio Observatory (C) the Chandra X-ray Observatory (D) the SOFIA airborne infrared observatory

(C) the Chandra X-ray Observatory

What are the Magellanic Clouds? (A) star-forming clouds found in the constellation Orion (B) two nebulae located in the disk of the Milky Way galaxy and visible only from the Southern Hemisphere (C) two small galaxies that orbit the Milky Way Galaxy (D) the clouds of dust and gas interspersed in many places throughout the Milky Way Galaxy

(C) two small galaxies that orbit the Milky Way Galaxy

Approximately how long does it take the Sun to orbit the center of the Milky Way Galaxy? (A) 200,000 years (B) 20,000 years (C) 2 billion years (D) 200 million years (E) 2 million years

(D) 200 million years

How does a black hole form from a massive star? (A) Any star more massive than 1.4 solar masses will undergo a supernova explosion and leave behind a black hole remnant (B) If enough mass is accreted by a white dwarf star that it exceeds the 1.4 solar mass limit, it will undergo a supernova explosion and leave behind a black-hole remnant (C) If enough mass is accreted by a neutron star, it will undergo a supernova explosion and leave behind a black-hole remnant (D) During a supernova, if the mass of the infalling core has enough gravity to overcome neutron degeneracy pressure, the core will collapse to a black hole (E) A black hole forms when two massive main-sequence stars collide

(D) During a supernova, if the mass of the infalling core has enough gravity to overcome neutron degeneracy pressure, the core will collapse to a black hole

Suppose you drop a clock toward a black hole. As you look at the clock from a high orbit, what will you notice? (A) The clock will fall toward the black hole at a steady rate, so that you'll see it plunge through the event horizon within just a few minutes (B) Time on the clock will run faster as it approaches the black hole, and light from the clock will be increasingly blueshifted (C) The clock will fall faster and faster, exceeding the speed of light as it crosses the event horizon (D) Time on the clock will run slower as it approaches the black hole, and light from the clock will be increasingly redshifted

(D) Time on the clock will run slower as it approaches the black hole, and light from the clock will be increasingly redshifted

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

(D) detecting the same changes at more than one location

The boundary from within which light cannot escape from a black hole is called the black hole's ____ (A) spacetime distortion zone (B) singularity (C) Schawarzschild radius (D) event horizon

(D) event horizon

The Sun's location in the Milky Way Galaxy is ____ (A) at the very outer edge of the galactic disk (B) very near the galactic center (C) in the halo of the galaxy, about 28,000 light-years above the galactic disk (D) in the galactic disk, slightly over halfway out from the center

(D) in the galactic disk, slightly over halfway out from the center

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

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

Gravitational waves were first detected directly in 2015. According to models, the source of these gravitational waves was ____ (A) a neutron star supernova (B) very powerful x-ray bursts (C) a white dwarf supernova (D) the merger of two black holes (E) the supernova of an extremely massive star

(D) the merger of two black holes

The first gravitational waves were detected in 2015 by the LIGO observatories in Washington and Louisiana. What event was thought to cause these gravitational waves? (A) a hypernova (B) ripples in spacetime left over from the Big Bang (C) two neutron stars merging (D) two black holes merging

(D) two black holes merging

What is the Schwarzschild radius of a 10-solar-mas black hole? (A) 30 billion km (B) 1 billion km (C) 10 km (D) 3 billion km (E) 30 km

(E) 30 km

After a massive-star supernova, what is left behind? (A) always a white dwarf (B) always a black hole (C) always a neutron star (D) either a white dwarf or a neutron star (E) either a neutron star or a black hole

(E) either a neutron star or a black hole

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

How do we know that the statement, " a 3-solar-mass black hole may be hidden between Jupiter and Saturn," is not true?

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

(True/False) A 3-solar-mass black hole may be hidden between Jupiter and Saturn

False

(True/False) A black hole will suck in any binary companion star

False

(True/False) Black holes emit x-ray light from within their event horizons

False

(True/False) You would be squashed by gravity at the event horizon of any black hole

False

How do we know the statement, "the singularity of a black hole has infinite density," is unknown?

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

(True/False) A black hole can form during a supernova explosion

True

(True/False) A black hole hole can have the mass of a star in space less than a few kilometers across

True

(True/False) A black hole is an object smaller than its own Schwarzschild radius

True

(True/False) Material from a binary companion can form an X-ray-emitting accretion disk around a black hole

True

(True/False) Two orbiting black holes can merge and emit gravitational waves

True

(True/False) Black holes make up 1% of the mass of the Milky Way Galaxy

Unknown

(True/False) The singularity of a black hole has infinite density

Unknown

How do we know the statement, "black holes make up 1% of the mass of the Milky Way Galaxy," is unknown?

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

Rank the following objects based on their mass, from largest to smallest: a typical neutron star, a typical black hole (formed in a supernova), a main-sequence star of spectral type M, and a 1-solar-mass white dwarf

a typical black hole (formed in a supernova), a typical neutron star, a 1-solar-mass white dwarf, and a main-sequence star of spectral type M

Rank the following stars based on the abundance of elements heavier than carbon you would expect to find, from highest to lowest abundance: a red main-sequence star in globular cluster M13, a hot/blue main-sequence star in open cluster in disk, a red giant in globular cluster M13, and a yellow main-sequence star in open cluster in disk

a yellow main-sequence star in open cluster in disk AND a hot/blue main-sequence star in open cluster in disk, and a red main-sequence star in globular cluster M13 AND a red giant in globular cluster M13

An ____ can form around a white dwarf, neutron star, or black hole in a binary system

accretion disk

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

A white dwarf can remain stable in size because of ____

electron degeneracy pressure

The ____ marks the boundary between the inside and outside of a black hole

event horizon

Rank the following objects based on their diameter, from largest to smallest: Jupiter, a 1-solar-mass white dwarf, the Moon, and a main-sequence star of spectral type A

main-sequence star of spectral type A, Jupiter, a 1-solar-mass white dwarf, and the Moon

A neutron star can remain stable in size because of ____

neutron degeneracy pressure

A ____ occurs when fusion ignites on the surface of a white dwarf

nova

A ____ is a rapidly rotating neutron star

pulsar

Rank the following stars based on their current age, from oldest to youngest: the Sun, a red main-sequence star in globular cluster M13, a hot and blue main-sequence star in disk, and a red giant in globular cluster M13

red giant in globular cluster M13 AND a red main-sequence star in globular cluster M13, the Sun, and a hot and blue main-sequence star in disk

The ____ is the place to which all of a black hole's mass is in principle located within a black hole

singularity

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

supermassive black hole

Rank the following objects based on their density from highest to lowest: a typical neutron star, the singularity of a black hole, a 1-solar-mass white dwarf, and a main-sequence star

the singularity of a black hole, a typical neutron star, a 1-solar-mass white dwarf, and a main-sequence star