A

Accretion disk - A disk of hot gas spiraling into a black hole

Angular momentum - A quantity related to the speed and mass of a rotating object

Axis - The imaginary pole down the center of a rotating object 

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B

Brown dwarf - A star with less than a tenth the mass of the sun that isn’t hot enough to transform hydrogen into helium

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C

Conservation of angular momentum - The scientific law that states no angular momentum can appear out of nowhere or disappear

Conservation of energy - The law in science that energy (or its equivalent in mass) can’t be either created or destroyed

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D

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E

Ergosphere - The area around a rotating black hole in which anything present will be dragged around the black hole in the
same direction the hole is spinning

Escape velocity - The speed necessary to escape the gravity of a massive body

Event horizon - The boundary of a black hole, which forms when the surface of a collapsing star reaches the radius where
light can no longer escape

Exclusion principle - The principle which states that two identical particles of matter can’t have both the same position and the same velocity

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G

Gravitational radiation - Energy emitted in the form of gravity waves by such things as collapsing stars

Gravitational redshift - The shift in wavelengths toward the red end of the spectrum, caused by a gravitational field

Graviton - The messenger particle of gravity, believed to travel at the speed of light

Gravity - A basic force of nature that always attracts

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H

Hydrogen atom - An atom with one proton in the nucleus and one electron

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K

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M

Matter - everything in the universe that is made up of matter particles is called matter. 

Matter particles - electrons, protons, neutrons, and the quarks that make up protons and neutrons. A more technical
definition of matter particle includes all particles, including photons and gravitons

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N

Neutron - A particle that is similar to a proton, but with zero electric charge, found in the nucleus of atoms. It’s made up of
three smaller particles called quarks

Neutron star - A cold star, about 20 miles in diameter. One of the ways a star can spend its old age. Exclusion principle
repulsion among its neutrons balances the pull of gravity

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P

Plasma - Ionized gas

Primordial black hole - A black hole created in the very early universe

Proton - One of the particles in the atomic nucleus. Protons have a positive electric charge and are made up of three
smaller particles called quarks
Pulsar - A neutron star that rotates very rapidly and sends out regular pulses of radio waves, sometimes several hundred to a thousand times a second

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Q

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R

Redshift - A shift in the wavelength of light (or other electromagnetic radiation) toward the red end of the spectrum

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S

Singularity - The dimensionless point at the center of a black hole, where all the mass of the collapsing star has shrunk to
infinite density

Solar mass - The mass of the sun

Speed of light - The speed at which light travels (about 186,300 miles per second)

Static, or stationary limit - The outside border of the ergosphere around a rotating black hole. Inside this limit nothing
can resist being dragged around the black hole in the direction in which the black hole is rotating

Supernova - The explosion of a star

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T

Time dilation - An effect caused by gravity or by acceleration in which the rate at which time passes in once location will be
measured differently by a clock right there and another clock somewhere else

Time-line - The usually vertical line in a diagram showing the time dimension

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W

White dwarf - A cold star, a few thousand miles in diameter. One of the ways a star can spend its old age. Exclusion
principle repulsion among its electrons balances the pull of gravity to keep it from collapsing

Wormhole - After a body falling into a rotating black hole is torn apart and reduced to elementary particles by tidal effects, it
may be possible for those particles to miss the singularity, travel through a small hole or tunnel in spacetime (called a
wormhole) to another universe or another part (or time) of our own universe

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X

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