ASTRO 101 CH. 14 HMW

25 July 2022
4.7 (114 reviews)
59 test answers

Unlock all answers in this set

Unlock answers (55)
question
Sorting Task: The Bizarre Stellar Graveyard Listed following are distinguishing characteristics of different end states of stars. Match these to the appropriate consequence of stellar death.
answer
White dwarf: -has a mass no greater than 1.4 MSun -in a binary systen, it can explode as a supernova -typically about the size(diameter) of Earth -supported by electron degeneracy pressure Neutron Star: -usually has a very strong magnetic field -sometimes appears as a pulsar Black hole: -viewed from afar, time stops at its event horizon -size defined by its Schwarzschild radius
question
Ranking Task: The Size of Planets, Stars, and Stellar Remnants 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 black holes to have greater masses than neutron stars.) (Jupiter, the Moon, the event horizon of a two solar mass black hole, a two solar mass neutron star, main sequence star of spectral type A, a one solar mass white dwarf)
answer
-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
question
The main-sequence star is obviously much larger than a planet such as Jupiter. A one-solar-mass white dwarf is about the size of Earth, which makes it larger than the Moon.
answer
A neutron star will be larger than a black hole of the same mass, because while light can escape from a neutron star, the same mass in a black hole must be more concentrated so that its gravity is strong enough to prevent light from escaping.
question
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.) (a typical neutron star, Jupiter, the Moon, a typical black hole-formed in a supernova, a one solar mass white dwarf, main sequence star of spectral type M)
answer
-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
question
Note that while the rankings shown are correct for "typical" white dwarfs, neutron stars, and black holes:
answer
each of these objects comes in a range of masses and so there may be some exceptions.
question
Listed following are several astronomical objects. Rank these objects based on their density, from highest to lowest. (a typical neutron star, a main sequence star, the singularity of a black hole, a one solar mass white dwarf)
answer
-the singularity of a black hole -a typical neutron star -a one solar mass white dwarf -a main sequence star
question
The singularity of a black hole:
answer
is a place where density approaches infinity, so it is clearly the most dense of the objects shown.
question
Neutron stars are much more dense than:
answer
white dwarfs, which in turn are much more dense than main-sequence stars.
question
Process of Science: Identifying Stellar Corpses 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.
answer
white dwarf: -may be surrounded by a planetary nebula -emits most strongly in visible and ultraviolet -may be in a binary system that undergoes nova explosions neutron star: -may be in a binary system that undergoes Xray bursts -can have a mass of 1.5 solar masses -may repeatedly dim and brighten more than once per second -may be surround by a supernova remnant
question
white dwarfs may be surrounded by:
answer
planetary nebulae because they are the remains of low-mass stars, while neutron stars form only in supernovae.
question
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 bin labeled "Both neutron stars and black holes."
answer
neutron star only: -may emit rapid pulses of radio waves -may be in a binary system that undergoes Xray bursts black hole only: is detectable only if it is accreting gas from other objects -can have a mass of 10 solar masses both neutron stars and black holes: -may be surrounded by a supernova remnant -may be located in an Xray binary
question
radio pulses and X-ray bursts cannot come from black holes, because both are caused by events that happen on the surface of a compact object.
answer
Note also that the fact that two important items go in the "Both" bin indicates that it can be more difficult to distinguish between neutron stars and black holes than between white dwarfs and neutron stars
question
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 reasonable conclusions about this system?
answer
-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
question
The system is an X-ray binary, which means the companion to the main-sequence star can be either a neutron star or a black hole.
answer
The X rays come from the hot accretion disk consisting of gas that the compact object's gravity is pulling away from the main-sequence star.
question
What is the key observation needed to determine whether the compact object in Part C is a neutron star or a black hole?
answer
measure Doppler shifts in the spectrum of the main sequence star so that you can determine the mass of the compact object
question
The Doppler shifts will allow you to determine the speed (or at least the component of the speed that is in your line of sight) of the main-sequence star as it orbits the compact object.
answer
You can then use this speed along with the known mass of the main-sequence star to determine the compact object's mass (or a lower limit on its mass). If this mass is greater than the neutron star limit of about 3 solar masses, then the object must be a black hole.
question
Sorting Task: Distinguishing Massive Star and White Dwarf Supernovae To distinguish between properties of the two major types of supernovae: massive star supernovae and white dwarf supernovae. All supernovae represent the explosions of stars, but current understanding suggests there are two basic types of supernovae: one that occurs when a massive star reaches the end of its life, and the other that occurs when a white dwarf star explodes because its mass has exceeded the white dwarf limit (also called the Chandrasekhar limit) of 1.4 solar masses.
answer
white dwarf supernova: ---spectra always lack strong hydrogen lines -can only occur in a binary system -can occur in a very old star cluster -star explodes completely leaving no compact object behind -has a brighter peak luminosity massive star supernova: -can only occur in a galaxy with ongoing star formation -black hole or neutron star left behind
question
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 understanding of supernovae.
answer
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 Surprising: -a young(5 million years) star explodes as a white dwarf supernova -an isolated star like our Sun explodes as a white dwarf supernova
question
the radius of a white dwarf is determined by a balance between the inward force of gravity and the outward push of:
answer
electron degeneracy pressure
question
a ____ occurs when hydrogen fusion ignites on the surface of a white dwarf in a binary system
answer
nova
question
a _______ occurs when fusion creates iron in the core of a star
answer
massive star supernova
question
a white dwarf in a close binary system will explode as a supernova if it gains enough mass to exceed the:
answer
white dwarf limit (1.4 solar masses)
question
A ________ consists of hot, swirling gas captured by a white dwarf (or neutron star or black hole) from a binary companion star.
answer
accretion disk
question
a _______ can occur only in a binary system, and all such events are thought to have the same luminosity
answer
white dwarf supernova
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
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?
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
From your point of view, time runs normally in your spaceship and gravity must accelerate you as you fall toward the black hole.
answer
There is no physical barrier at the event horizon, so you cross it unhindered.
question
Which of these objects has the smallest radius? -a 1.2Msun white dwarf -a 0.6Msun white dwarf -Jupiter
answer
-a 1.2 Msun white dwarf
question
If we see a nova, we know that we are observing:
answer
a white dwarf in a binary system
question
Which of these isolated neutron stars must have had a binary companion?
answer
an isolated pulsar that pulses 600 times per second
question
What would happen to a neutron star with an accretion disk orbiting in a direction opposite to the neutron star's spin
answer
its spin would slow down
question
In a massive star supernova explosion, a stellar core collapses down to form a neutron star roughly 10 kilometers in radius. The gravitational potential energy released in such a collapse is approximately equal to GM2r where M is the mass of the neutron star, r is its radius, and G=6.67×10−11m3/kg×s2 is the gravitational constant. Using this formula, estimate the amount of gravitational potential energy released in a massive star supernova explosion.
answer
~10^47 jouls
question
In a massive star supernova explosion, a stellar core collapses down to form a neutron star roughly 10 kilometers in radius. The gravitational potential energy released in such a collapse is approximately equal to GM2r where M is the mass of the neutron star, r is its radius, and G=6.67×10−11m3/kg×s2 is the gravitational constant. How does it compare with the amount of energy released by the Sun during its entire main-sequence lifetime?
answer
(Esupernova explosion)/ (Esun total) ~ 10^2
question
Which of these objects has the largest radius? -1.2 Msun white dwarf -1.5 Msun neutron star -3.0 Msun black hole
answer
1.2 Msun white dwarf
question
Viewed from a distance, how would a flashing red light appear as it fell into a black hole?
answer
Its flashes would shift to the infrared part of the spectrum
question
Which of these black holes exerts the weakest tidal forces on an object near its event horizon? -10Msun black hole -100Msun black hole -10^6Msun black hole
answer
10^6 Msun black hole
question
What would happen if the Sun suddenly became a black hole without changing its mass?
answer
earths orbit would not change
question
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 - a binary with an X-ray burster - an X-ray binary containing a G star and another object of equal mass
answer
an X-ray binary containing an O star and another object of equal mass
question
Calculate the Schwarzschild radius (in kilometers) for each of the following. A 108MSun black hole in the center of a quasar
answer
3.00 x 10^8 km
question
Calculate the Schwarzschild radius (in kilometers) for each of the following. A 5MSun black hole that formed in the supernova of a massive star.
answer
15 km
question
Calculate the Schwarzschild radius (in kilometers) for each of the following. A mini-black hole with the mass of the Moon.
answer
1.10 x 10^-7 km
question
Calculate the Schwarzschild radius (in kilometers) for each of the following. A miniblack hole formed when a superadvanced civilization decides to punish you (unfairly) by squeezing you until you become so small that you disappear inside your own event horizon. (Assume that your mass is 50 kg.)
answer
7.40 x 10^-29 km
question
Where do gamma-ray bursts tend to come from?
answer
extremely distant galaxies
question
At peak brightness, the white dwarf supernova is approximately __________ times as luminous as the massive star supernova at its peak brightness.
answer
3
question
For the white dwarf supernova, the luminosity 175 days after it reaches peak brightness is about __________ of the luminosity at peak brightness
answer
1%
question
Approximately how many days does it take for a white dwarf supernova to decline to 10% of its peak brightness?
answer
30 days
question
Approximately how many days does it take for a massive star supernova to decline to 10% of its peak brightness?
answer
100 days
question
Approximately how many days does it take for a massive star supernova to decline to 1% of its peak brightness?
answer
300 days
question
consider three planets. All have the same mass as Earth but with different radii. For which planet is the escape velocity from the surface the largest? Planet 1 = ___________________ Planet 2 = ______________ Planet 3 = _________
answer
Planet 3
question
the event horizon of a 3 solar mass black hole is roughly the same size as:
answer
a small town
question
the event horizon for a 10 solar mass black hole is:
answer
larger than that of a 1 solar mass black hole
question
which of the following is true about observational evidence for black holes?
answer
we have inferred the presence of supermassive black holes in many galaxies
question
some Xray binaries are candidates for black holes because:
answer
the object in the center of the accretion disk is too massive to be a neutron star
question
if you could measure the orbital speeds of particles in an accretion disk around a black hole, you would notice that:
answer
particles near the center are moving fastest
question
if jupiter turned into a black hole:
answer
Earth would continue orbiting the Sun, unaffected by this event
question
what makes us think that black holes really exist?
answer
we have observed orbital motions around objects so compact that according to current understandings, they must be black holes