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A brown dwarf.
A white dwarf.
A neutron star.
A very massive main-sequence star.
The central core of the Sun after hydrogen fusion ceases but before helium fusion begins.
They are both very hot and very small.
They are the end-products of small, low-mass stars.
They are the opposite of black holes.
It amplifies the contrast with red giants.
They are supported by electron degeneracy pressure.
The same as a teaspoonful of Earth-like material.
About the same as Mt. Everest.
About the same as the earth.
A few tons.
A few million tons.
It will cool down and become a cold black dwarf.
As gravity overwhelms the electron degeneracy pressure, it will explode as a nova.
As gravity overwhelms the electron degeneracy pressure, it will explode as a supernova.
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.
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.
The white dwarf immediately collapses into a black hole, disappearing from view.
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.
Neutron degeneracy pressure
Electron degeneracy pressure
All of the above
There is no upper limit.
There is an upper limit, but we do not yet know what it is.
2 solar masses
1.4 solar masses
1 solar mass
It has a larger radius.
It has a smaller radius.
It has a higher surface temperature.
It has a lower surface temperature.
It is supported by neutron, rather than electron, degeneracy pressure.
A small city
A football stadium
Always a white dwarf
Always a neutron star
Always a black hole
Either a white dwarf or a neutron star
Either a neutron star or a black hole
About the same as a teaspoonful of Earth-like material.
A few tons.
More than Mt. Everest.
More than the Moon.
More than the earth.
A football stadium
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 flashes of light several times per second or more, with near perfect regularity
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
The star vibrates.
As the star spins, beams of radio radiation sweep through space. If one of the beams crosses the 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.
A black hole near the star absorbs energy and re-emits it as radio waves.
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.
Any star that is more massive than 8 solar masses will undergo a supernova explosion and leave behind a black-hole remnant.
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.
A black hole forms when two massive main-sequence stars collide.
If you watch someone else fall into a black hole, you will never see him or her cross the event horizon. However, he or she will fade from view as the light he or she emits (or reflects) becomes more and more redshifted.
If we watch a clock fall toward a black hole, we will see it tick slower and slower as it falls nearer to the black hole.
A black hole is truly a hole in spacetime, through which we could leave the observable universe.
If the Sun magically disappeared and was replaced by a black hole of the same mass, the earth would soon be sucked into the black hole.
If you fell into a black hole, you would experience time to be running normally as you plunged rapidly across the event horizon.