Stars, Galaxies, The Universe
black hole
A black hole is defined as a region of spacetime from which gravity prevents anything, including light, from escaping. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole
Nebula
A nebula is an interstellar cloud of dust, hydrogen, helium and other ionized gases.
protostar
A protostar is a large mass that forms by contraction out of the gas of a giant molecular cloud in the interstellar medium. The protostellar phase is an early stage in the process of star formation.
red giant
A red giant is a luminous giant star of low or intermediate mass (roughly 0.3-8 solar masses (M☉)) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low,
white dwarf
A white dwarf, also called a degenerate dwarf, is a stellar remnant composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun, and its volume is comparable to that of the Earth.
main sequence star
Main sequence stars are stars that are fusing hydrogen atoms to form helium atoms in their cores. Most of the stars in the universe are main sequence stars
galaxy
a collection of stars, dust, and gas bound together by gravity
supernova
a gigantic explosion in which a massive star collapses and throws its outer layers into space
cluster
a group of stars and galaxies bound by gravity
doppler effect
an observed change in the frequency of a wave when the source or observer is moving
quasar
quasi-stellar radio source a very luminous object that produces energy at a high rate, thought to be the most distant objects in the universe
lightyear
the distance that light travels in one year, 9.46 trillion kilometers
interstellar matter
the gas and dust located between stars in a galaxy
universe
the sum of all space, matter, and energy that exist, that have existed in the past and that will exist in the future.
big bang theory
the theory that all matter and energy in the universe was compressed into an extremely small volume that 15 billion years ago exploded and began expanding in all directions
