A white dwarf is __________
what most stars become when they die
A typical white dwarf is __________
as massive as the sun but only about as large as the earth
If you had something the size of a sugar cube that was made of white dwarf matter, it would weigh
as much as a truck
The maximum mass of a white dwarf is ___________
about 1.4 times the mass of our sun
What is an accretion disk?
a disk of hot gas swirling rapidly around a white dwarf, neutron star, or black hold
According to our modern understanding, what is a nova?
an explosion on the surface of a white dwarf in a close binary system
Suppose that a white dwarf is gaining mass through accretion in a binary system. What happens if it someday reaches the 1.4 solar mass limit?
the white dwarf will explode completely as a white dwarf supernova
A neutron star is ________________.
the remains of a star that died in a massive star supernova (if no black hole was created)
A typical neutron star is more massive than our Sun and about the size (radius) of
a small asteroid (10 km in diameter)
If you had something the size of a sugar cube that was made if neutron star matter, it would weigh ____________.
about as much as a large mountain
Pulsars are thought to be __________.
rapidly rotating neutron stars
How is a X-ray burst (in a X-ray binary star system) similar to a nova?
both involve explosions on the surface of a stellar corpse
What is the basic definition of a black hole?
an object with gravity so strong that not even light can escape
Based on current understanding, the minimum mass of a black hole that forms during a massive star supernova is roughly _________.
3 solar masses
What do we mean by the event horizon of a black hole?
it is the point beyond which light nor anything else can escape
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?
nothing- earth's orbit would stay the same
What do we mean by the singularity of a black hole?
it is the center of the black hole, a place of infinite destiny where the known laws of physics cannot describe the conditions
What makes us think that the star system Cygnus X-1 contains a black hole?
it emits x-ray characteristic of an accretion disk, but the unseen star in the system is too massive to be a neutron star
The Schwarzschild radius of a black hole depends on ______.
only the mass of a black hole
Based on current evidence, which of the following statements about gamma ray bursts is true?
all those that we have detected occurred in distant galaxies
Which of the following statements about electron degeneracy pressure and neutron degeneracy pressure is true?
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 about degeneracy pressure is not true?
Degeneracy pressure can arise only from interactions with electrons
The more massive the white dwarf, the _____
smaller its radius
Which of the following best describes why a white dwarf cannot have a mass greater than the 1.4-solar-mass limit?
Electron degeneracy pressure depends on the speeds of electrons, which approach the speed of light as a white dwarf's mass approaches the 1.4 solar mass limit.
The white dwarf that remains when our Sun dies will be mostly made of __________.
carbon
Which statement about accretion disks is not true?
The primary factor determining whether a white dwarf has an accretion disk is the white dwarf's mass.
According to present understanding, a nova is caused by ___________.
hydrogen fusion on the surface of a white dwarf
Which of the following is NOT true about differences between nova and supernova?
Supernovae eject gas into space but novae do not
Will our Sun ever undergo a white dwarf supernova explosion? Why or why not?
No, because it is not orbited by another star
Which of the following best describes what would happen if a 1.5 solar mass neutron star, with a diameter of few kilometers, were suddenly (for unexplained reasons) to appear in your home town?
The entire Earth would end up as a thin layer, about 1 cm thick, over the surface of the neutron star
Each Voyager spacecraft carries a "postcard" designed to be understandable to any aliens that might someday encounter it. On the "postcard" pinpointed the location of Earth by triangulating it between pulsars. Why did the scientists choose pulsars rather
Pulsars are easy to identify by their almost perfectly stead periods of pulsation
Which statement about pulsars is not thought to be true?
Pulsars can form only in close binary systems
How does an accretion disk around a neutron star differ from an accretion disk around a white dwarf?
The accretion disk around a neutron star is much hotter and emits higher-energy radiation
Which statement concerning black hole masses and Schwarzschild radii is not true?
In a binary system with a black hole, the Schwarzschild radius depends on the distance from the black hole to the comparison star
Suppose you drop a clock toward a black hole. As you look at the clock from a high orbit, what will you notice?
Time on the clock will run slower as it approaches the black hole, and light from the clock will be increasingly redshifted
Which statement below about black holes is NOT true?
A spaceship passing near a 10 solar mass black hole is much more likely to be destroyed than a spaceship passing at the same distance from the center of a 10 solar mass main-sequence star.
When we see X rays from an accretion disk in a binary system, we can't immediately tell whether the accretion disk surrounds a neutron star or a black hole. Suppose we then observe each of the following phenomena in this system. Which one would rule out t
intense X ray bursts
Which of the following observatories is most likely to discover a black hole in a binary system?
the Chandra X-ray Observatory
Which of the following statements about gamma ray bursts is NOT true?
The events responsible for gamma ray bursts apparently produce only gamma rays, and no other light that we can hope to detect
Imagine an advanced civilization living on a plant orbiting at a distance of 10 AU (1.5 billion kilometers) from a close binary star system that consists of a 15Msun red giant star and 10 Msun black hole. The black hole is surrounded by an accretion disk.
the red giant will probably supernova within the next million years
Consider again the civilization described in the previous question. (They live on a planet orbiting 10 AU from a close binary star system that consists of a 15 Msun red giant star and a 10M sun black hole surrounded by an accretion disk). One foolhardy da
X rays from the accretion disks
Consider again the civilization described in the previous question. (They live on a planet orbiting 10 AU from a close binary star system that consists of 15Msun red giant star and a 10Msun black hole surrounded by an accretion disk.) Through a bizarre (a
They evolved on a different planet in a different star system, and moved to their current location.