Option D: Astrophysics

Two stars orbiting a common centre

The remnant of a white dwarf after it has cooled down. It has very low luminosity.

A singularity in space time; the end result of the evolution of a very massive star

Gas and dust that did not reach high enough temperatures to initiate fusion. These objects continue to compact and cool down.

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.

Galaxies close to one another and affecting one another gravitationally, behaving as one unit

a small body of ice, rock, and cosmic dust orbiting the Sun in an elliptical orbit

A group of stars in a recognisable pattern that ‘appear’ to be near each other in space

Generic name for matter in galaxies and clusters of galaxies that is too cold to radiate. Its existence is inferred from techniques other than direct visual observation

A collection of a very large number of stars mutually attracting one another through the gravitational force and staying together.

Gases (mainly hydrogen and helium) and dust grains (silicates, carbon and iron) filling the space in between stars, the density of interstellar mass is very low.

A normal star that is undergoing nuclear fusion of hydrogen into helium. Our sun is a typical main sequence star.

Clouds of ‘dust’, i.e. compounds of carbon, oxygen, silicon and metals, as well as molecular hydrogen in the space in between stars

The end result of the explosion of a red supergiant; a very small star a few tens of kilometres in diameter, and very dense. It consists almost entirely of neutrons which form a superfluid around a core of immense pressure and density.

The ejected envelope of a red giant star

A very small star with low temperature, reddish in colour.

A main-sequence star evolves into a red giant – a very large, reddish star. There are nuclear reactions involving the fusion of helium into heavier elements.

A group of stars that physically near each other in space, created by the collapse of a single gas cloud.

The explosion of a white dwarf that has accreted mass from a companion star exceeding its stability limit

The explosion of a red supergiant star: The amount of energy emitted in a supernova explosion can be staggering – comparable to the total energy radiated by our Sun in its entire lifetime!

The end result of the explosion of a red giant. A small, dense star (about the size of the Earth), in which no nuclear reactions take place – very hot but its small size gives it a very low luminosity

Large numbers of mainly old, evolved stars

Small numbers of young stars (some are very hot) that are further apart

Collections of clusters of galaxies

Nuclei of hydrogen fuse to produce helium and energy

The sequence of nuclear fusion reactions that take place in stellar interiors