IB Physics Option D Astrophysics Definitions
Two stars orbiting a common centre
The remnant of a white dwarf after it has cooled down. It has very low luminosity
A singularity that is the end result of the evolution of a very massive star
A star of variable luminosity. The luminosity increases sharply and falls off gently with a well-defined period. The period is related to the absolute luminosity of the star and so can be used to estimate the distance to the star
Cluster of galaxies
Galaxies close to one another and affecting one another gravitationally, behaving as one unit
A group of stars in a recognizable pattern that appear to be near each other in space
Matter in galaxies that is too cold to radiate. Its existence is inferred from techniques other than direct visual observation
A collection of very large number of stars held together by gravitational forces
Main sequence star
A normal star that is undergoing nuclear fusion of hydrogen into helium.
The end result of the explosion of a red super giant. A very dense star consisting of neutrons
A celestial body that orbits a star
Gravitationally bounded non-stellar objects in orbit around a star or star system.
The ejected envelope of a red giant star
A cloud of dust, hydrogen, helium and other ionized gases.