A typical white dwarf is _________.
as massive as the Sun but only about as large in size as Earth
The maximum mass of a white dwarf is _________.
about 1.4 times the mass of our Sun
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 the mass someday reaches the 1.4 solar mass limit?
The white dwarf will explode completely as a white dwarf supernova.
Choose the correct description, of what happens to the electron speeds in a more massive white dwarf.
As the mass of a white dwarf increases, the pressure must increase to resist gravity. To do this, the electrons must move faster.
Choose the correct description, how does this behavior lead to the white dwarf limit for mass.
If mass of the white dwarf becomes so great that the electrons would have to move faster than light to resist the gravity, the white dwarf must collapse into a neutron star. This limit is about 1.4 MSun.
Choose the correct description of what accretion disks are, and why do we find them only in close binary systems.
An accretion disk is a disk of orbiting material that is falling toward a central body, like a white dwarf. We see these only in close binary systems because they require material to be transferred from one star to another.
Choose the correct explanation of how does the accretion disk provide a white dwarf with a new source of energy that we can detect from Earth.
As the material falls onto a white dwarf, gravitational energy is turned into heat. The heat provides the white dwarf with a new energy source, allowing it to glow in the ultraviolet.
Choose the correct description of processes, which cause a white dwarf supernova.
A white dwarf supernova occurs when the white dwarf gains enough mass for the carbon interior of the star to begin carbon fusion. The fusion begins almost instantly throughout the star, so the entire star ignites and the white dwarf explodes completely.
Choose the correct way to distinguish white dwarf and massive star supernovae observationally.
These supernovae, unlike the massive star supernovae, lack hydrogen lines in their spectra, allowing astronomers to tell the two types of supernovae apart.
Which of these objects has the smallest radius?
a 1.2MSunwhite dwarf
A typical neutron star is more massive than our Sun and about the size (radius) of _________.
a small asteroid (10 km in diameter)
Pulsars are thought to be _________.
rapidly rotating neutron stars
How is an X-ray burst (in an X-ray binary system) similar to a nova?
Both involve explosions on the surface of a stellar corpse.
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.
What would happen to a neutron star with an accretion disk orbiting in a direction opposite to the neutron star's spin?
Its spin would slow down.
Which of these neutron stars must have had its angular momentum changed by a binary companion?
Which of these neutron stars must have had its angular momentum changed by a binary companion?
a pulsar that pulses 600 times per second
What do we mean by the event horizon of a black hole?
It is the point beyond which neither 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 remain the same.
What makes us think that the star system Cygnus X-1 contains a black hole?
It emits X-rays 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 the black hole
Which of these objects has the largest radius?
a 1.2MSunwhite dwarf
What would happen if the Sun suddenly became a black hole without changing its mass?
Earth would remain in the same orbit.
Which of these binary systems is most likely to contain a black hole?
an X-ray binary containing an O star and another object of equal mass
Viewed from a distance, how would a flashing red light appear as it fell into a black hole?
Its flashes would shift to the infrared part of the spectrum.
Which of these black holes exerts the weakest tidal force on an object near its event horizon?
a 106MSun 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.
Where do gamma-ray bursts tend to come from?
extremely distant galaxies
To understand how observations allow scientists to determine whether a compact object is a white dwarf, neutron star, or black hole.
SEE NEXT
The following items describe observational characteristics that could indicate that an object is either a white dwarf or a neutron star. Match each characteristic to the correct object.
WD: may be surrounded by a planetary nebula.
emits most strongly in visible and ultraviolet.
may be in a binary system that undergoes nova explosions.
NS: may be in a binary system that undergoes X-ray bursts.
can have a mass of 1.5 solar masses.
may be s
The following items describe observational characteristics that may indicate that an object is either a neutron star or a black hole. Match each characteristic to the correct object; if the characteristic could apply to both types of object, choose the bi
NS: may emit rapid pulses of radio waves.
may be in a binary system that undergoes X-ray bursts.
BH: is detectable only if it is accreting gas from other objects.
can have a mass of 10 solar masses.
Both: may be located in an X-ray binary.
may be surround
The Chandra X-Ray Observatory has detected X rays from a star system that contains a main-sequence star of spectral type B6. The X-ray emission is strong and fairly steady, and no sudden bursts have been observed. Which of the following statements are rea
-The main-sequence star orbits either a neutron star or a black hole.
-Gas from the main-sequence star makes an accretion disk around another object.
What is the key observation needed to determine whether the compact object in Part C is a neutron star or a black hole?
Measure Doppler shifts in the spectrum of the main-sequence star so that you can determine the mass of the compact object.
Listed following are several astronomical objects. Rank these objects based on their diameter, from largest to smallest. (Note that the neutron star and black hole in this example have the same mass to make your comparison easier, but we generally expect
largest diameter to smallest diameter.
main-sequence star of spectral type A, Jupiter, a one-solar-mass white dwarf, the Moon, a two-solar-mass neutron star, the event horizon of a two-solar-mass black hole
Listed following are several astronomical objects. Rank these objects based on their mass, from largest to smallest. (Be sure to notice that the main-sequence star here has a different spectral type from the one in Part A.)
largest mass to smallest mass.
a typical black hole (formed in a supernova), a typical neutron star, a one-solar-mass white dwarf, main-sequence star of spectral type M, Jupiter, the Moon
Listed following are several astronomical objects. Rank these objects based on their density, from highest to lowest.
highest density to lowest density.
the singularity of a black hole, a typical neutron star, a one-solar-mass white dwarf, a main-sequence star
Listed following are distinguishing characteristics of different end states of stars. Match these to the appropriate consequence of stellar death.
WD: in a binary system, it can explode as a supernova.
has mass no greater than 1.4 MSun.
typically about the size (diameter) of Earth.
supported by electron degeneracy pressure.
NS: sometimes appears as a pulsar.
usually has a very strong magnetic field.
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?
Time runs increasingly slower as the rocket approaches the black hole.
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
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?
Its light will become so redshifted that it will be undetectable.
If you were inside the rocket that falls toward the event horizon, you would notice your own clock to be running __________.
at a constant, normal rate as you approach the event horizon
If you were inside the rocket that falls toward the event horizon, from your own viewpoint you would __________.
accelerate as you fall and cross the event horizon completely unhindered
Match the items below with the correct type of supernova.
WD: Can only occur in a binary system.
Spectra always lack strong hydrogen lines.
Can occur in a very old star cluster.
Star explodes completely, leaving no compact object behind.
Has a brighter peak luminosity.
MSS: Black hole or neutron star left behind
Each item below describes an observation of a hypothetical supernova. Classify each observation as either "Not surprising" if it fits in with our current understanding of supernovae, or "Surprising" if the observation would cause us to rethink our underst
Not surprising: A white dwarf supernova in a galaxy of only old stars.
Two massive star supernovae occur in the same young star cluster.
A massive star supernova leaves behind no detectable compact object.
A massive star in a binary system explodes.
Surpr
Match the words in the left-hand column to the appropriate blank in the sentences in the right-hand column. Use each word only once.
CONTINUE
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
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) ______ consists of hot, swirling gas captured by a white dwarf (or neutron star or black hole) from a binary companion star.
accretion disk
A(n) ______ occurs when hydrogen fusion ignites on the surface of a white dwarf in a binary system.
nova
A(n) ______ can occur only in a binary system, and all such events are thought to have about the same luminosity.
white dwarf supernova
A(n) ______ occurs when fusion creates iron in the core of a star.
massive star supernova