Assignment 08 Chapter 18 The Bizarre Stellar Graveyard – Flashcards

Degeneracy pressure is the source of the pressure that stops the crush of gravity in all the following except ANSWER: a brown dwarf. the central core of the Sun after hydrogen fusion ceases but before helium fusion begins. a neutron star. a white dwarf. a very massive main-sequence star.

White dwarfs are so called because ANSWER: they are the opposite of black holes. it amplifies the contrast with red giants. they are both very hot and very small. they are the end-products of small, low-mass stars. they are supported by electron degeneracy pressure.

Which of the following is closest in mass to a white dwarf? ANSWER: Jupiter Earth the Moon the Sun

Why is there an upper limit to the mass of a white dwarf? ANSWER: The more massive the white dwarf, the higher its temperature and hence the greater its degeneracy pressure. At about 1.4 solar masses, the temperature becomes so high that all matter effectively melts, even individual subatomic particles. The more massive the white dwarf, the greater the degeneracy pressure and the faster the speeds of its electrons. Near 1.4 solar masses, the speeds of the electrons approach the speed of light, so more mass cannot be added without breaking the degeneracy pressure. The upper limit to the masses of white dwarfs was determined through observations of white dwarfs, but no one knows why the limit exists. White dwarfs come only from stars smaller than 1.4 solar masses.

What is the ultimate fate of an isolated white dwarf? ANSWER: As gravity overwhelms the electron degeneracy pressure, it will explode as a nova. It will cool down and become a cold black dwarf. As gravity overwhelms the electron degeneracy pressure, it will become a neutron star. The electron degeneracy pressure will eventually overwhelm gravity and the white dwarf will slowly evaporate. As gravity overwhelms the electron degeneracy pressure, it will explode as a supernova.

What kind of pressure supports a white dwarf? ANSWER: electron degeneracy pressure thermal pressure radiation pressure neutron degeneracy pressure all of the above

Suppose a white dwarf is gaining mass because of accretion in a binary system. What happens if the mass someday reaches the 1.4-solar-mass limit? ANSWER: A white dwarf can never gain enough mass to reach the limit because a strong stellar wind prevents the material from reaching it in the first place. The white dwarf immediately collapses into a black hole, disappearing from view. The white dwarf undergoes a catastrophic collapse, leading to a type of supernova that is somewhat different from that which occurs in a massive star but is comparable in energy. The white dwarf, which is made mostly of carbon, suddenly becomes much hotter in temperature and therefore is able to begin fusing the carbon. This turns the white dwarf back into a star supported against gravity by ordinary pressure.

What is the upper limit to the mass of a white dwarf? ANSWER: There is an upper limit, but we do not yet know what it is. There is no upper limit. 1 solar mass 2 solar masses 1.4 solar masses

Which of the following is closest in size (radius) to a white dwarf? ANSWER: a football stadium the Sun a small city Earth a basketball

What kind of star is most likely to become a white-dwarf supernova? ANSWER: a white dwarf star with a red giant binary companion an O star a binary M star a star like our Sun a pulsar

Observationally, how can we tell the difference between a white-dwarf supernova and a massive-star supernova? ANSWER: The light of a white-dwarf supernova fades steadily, while the light of a massive-star supernova brightens for many weeks. A massive-star supernova happens only once, while a white-dwarf supernova can repeat periodically. A massive-star supernova is brighter than a white-dwarf supernova. The spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white-dwarf supernova does not. We cannot yet tell the difference between a massive-star supernova and a white-dwarf supernova

After a massive-star supernova, what is left behind? ANSWER: always a black hole always a neutron star either a white dwarf or a neutron star either a neutron star or a black hole always a white dwarf

What is the upper limit to the mass of a neutron star? ANSWER: 1 solar mass 1.4 solar masses There is no upper limit. There is an upper limit less than 3 solar masses, but we do not yet know precisely what it is. precisely 2 solar masses

Which of the following is closest in size (radius) to a neutron star? ANSWER: a football stadium the Sun a city Earth a basketball

From an observational standpoint, what is a pulsar? ANSWER: 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 an object that emits random "pulses" of light that sometimes occur only a fraction of a second apart and other times stop for several days at a time a star that changes color rapidly, from blue to red and back again an object that emits flashes of light several times per second or more, with near perfect regularity

What causes the radio pulses of a pulsar? ANSWER: A black hole near the star absorbs energy and re-emits it as radio waves. As the star spins, beams of radio radiation sweep through space. If one of the beams crosses Earth, we observe a pulse. The star undergoes periodic explosions of nuclear fusion that generate radio emission. The star's orbiting companion periodically eclipses the radio waves emitted by the main pulsar. The star vibrates.

From a theoretical standpoint, what is a pulsar? ANSWER: a neutron star or black hole that happens to be in a binary system a star that is burning iron in its core a rapidly rotating neutron star a star that alternately expands and contracts in size a binary system that happens to be aligned so that one star periodically eclipses the other

What is the basic definition of a black hole? ANSWER: any object from which the escape velocity exceeds the speed of light any compact mass that emits no light a dead galactic nucleus that can only be viewed in infrared a dead star that has faded from view any object made from dark matter

How does the gravity of an object affect light? ANSWER: Light doesn't have mass; therefore, it is not affected by gravity. Less energetic light will not be able to escape from a compact massive object, such as a neutron star, but more energetic light will be able to. Light coming from a compact massive object, such as a neutron star, will be redshifted. Visible light coming from a compact massive object, such as a neutron star, will be redshifted, but higher frequencies such as X rays and gamma rays will not be affected. Light coming from a compact massive object, such as a neutron star, will be blueshifted.

How does a black hole form from a massive star? ANSWER: A black hole forms when two massive main-sequence stars collide. If enough mass is accreted by a white-dwarf star so that it exceeds the 1.4-solar-mass limit, it will undergo a supernova explosion and leave behind a black-hole remnant. If enough mass is accreted by a neutron star, it will undergo a supernova explosion and leave behind a black-hole remnant. Any star that is more massive than 8 solar masses will undergo a supernova explosion and leave behind a black-hole remnant. During a supernova, if a star is massive enough for its gravity to overcome neutron degeneracy of the core, the core will be compressed until it becomes a black hole.

What do we mean by the singularity of a black hole? ANSWER: It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions. There are no binary black holes â each one is isolated. It is the edge of the black hole, where one could leave the observable universe. An object can become a black hole only once, and a black hole cannot evolve into anything else. 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. Correct

If you were to come back to our Solar System in 6 billion years, what might you expect to find? ANSWER: a rapidly spinning pulsar a white dwarf a red giant star a black hole Everything will be pretty much the same as it is now.

Brown dwarfs, white dwarfs, and neutrons stars are all kept from collapsing by degeneracy pressure. ANSWER: True False

The upper limit to the mass of a white dwarf is 1.4 solar masses. ANSWER: True False

More massive white dwarfs are smaller than less massive white dwarfs ANSWER: True False

Our Sun will likely undergo a nova event in about 5 billion years. ANSWER: True False

All pulsars are neutron stars, but not all neutron stars are pulsars. ANSWER: True False

All massive-star supernovae leave behind black holes as remnants. ANSWER: True False

Which of these objects has the smallest radius? ANSWER: a 1.2MSunwhite dwarf a 0.6MSun white dwarf Jupiter

Which of these objects has the largest radius? ANSWER: a 1.2MSunwhite dwarf a 1.5MSun neutron star a 3.0MSun black hole

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 speed up. Its spin would slow down. Its spin would stay the same.

Where do gamma-ray bursts tend to come from? ANSWER: neutron stars in our galaxy black holes in our galaxy extremely distant galaxies

What is the Schwarzschild radius of a 267 million-solar-mass black hole? The mass of the Sun is about 2×1030kg, and the formula for the Schwarzschild radius of a black hole of mass M is: Rs=2GMc2 (G=6.67×10−11m3kg×s2; c=3×108m/s) ANSWER: 8 million km 80 km 800 million km 8000 km 8 km

A 2×108 MSun black hole in the center of a quasar. Express your answer using two significant figures. ANSWER:

A 5 MSun black hole that formed in the supernova of a massive star. Express your answer using two significant figures.

A mini-black hole with the mass of the Moon. Express your answer using two significant figures.

Estimate the Schwarzschild radius (in kilometers) for a mini-black 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 the your weight is 50 kg) Express your answer using one significant figure.