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black hole  A region of space from which no matter or radiation can escape. A black hole is a result of the extreme curvature of space by a massive compact body.
Chandrasekhar limit  The maximum mass, about 1.4 solar masses, that a white dwarf star can have.
event horizon  The boundary of a black hole. No matter or radiation can escape from within the event horizon.
geodesic  The path in spacetime followed by a light beam or a freely moving object.
gravitational redshift  The increase in the wavelength of electromagnetic radiation that occurs when the radiation travels outward through the gravitational field of a body.
magnetar  A highly magnetized neutron star that emits bursts of gamma rays.
neutron star  A star composed primarily of neutrons and supported by the degenerate pressure of the neutrons.
neutronization  A process by which, during the collapse of the core of a star, protons and electrons are forced together to make neutrons.
pulsar  A rotating neutron star with beams of radiation emerging from its magnetic poles. When the beams sweep past the Earth, we see "pulses" of radiation.
Schwarzschild radius  The radius of the event horizon of a blackhole.
spacelike trip  A path in spacetime that would require motion at a speed faster than the speed of light.
spacetime  The combination of three spatial coordinates and one time coordinate that we use to locate an event.
spacetime diagram  A diagram showing one spatial coordinate against time, in which the paths of bodies and beams of light can be plotted.
supernova  An explosion in which a star’s brightness temporarily increasesby as much as 1 billion times. Type I supernovae are caused by the rapid fusion of carbon and oxygen within a white dwarf. Type II supernovae are produced by the collapse of the core of a star.
supernova remnant  The luminous, expanding region of gas driven outward by a supernova explosion.
synchrotron emission  Electromagnetic radiation, usually observed in the radio region of the spectrum, produced by energetic electrons spiraling about magnetic field lines.
timelike trip  A path in spacetime that can be followed by a body moving slower than the speed of light.
type II supernova  An extremely energetic explosion that occurs when the core of a massive star collapses, probably producing a neutron star or black hole.
white dwarf  A small, dense star that is supported against gravity by the degenerate pressure of its electrons.

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