A1 Stars definitions

Nebulae

Gigantic clouds of dust and gas, often many hundreds of times larger than our solar system. They are the birthplace of all stars

Planets

An object in orbit with a mass large enough for its own gravity to give it a round shape. It has no fusion reactions and has cleared its orbit of most other objects.

Dwarf planets

The difference between a dwarf planet and a planet is that dwarf planets have not cleared their orbit of other objects

Asteroids

Objects too small and uneven to be planets, usually in near circular orbits round the Sun and without the ice present in comets

Planetary satellites

A body in orbit around a planet. This includes moons and man-made satellites.

Comets

Small irregular bodies made up of ice, dust and rock. All comets orbit the sun, many in highly eccentric elliptical orbits

Solar system

A planetary system consisting of a star and at least one planet in orbit around it

Galaxy

A collection of stars and interstellar dust and gas bound together by their mutual gravitational force

Universe

Everything that exists within space and time

Protostar

A very hot, very dense sphere of condensing dust and gas that is on the way to becoming a star

Fusion

A process in which two smaller nuclei join together to form one larger nucleus

Main sequence

The main period on a H-R diagram in a stars life, during which it is stable

Brown dwarfs

Stars with masses less than 0.08 Msun never become hot enough to burn hydrogen and don’t make it onto the main sequence. Smaller stars continue contracting forming brown dwarfs.

Red giant

An expanding star at the end of its life, with an inert core in which fusion no longer takes place, but in which fusion of lighter elements continues in the shell around the core

Red supergiant

A huge star in the last stages of its life, before it ‘explodes’ in a supernova

White dwarf

A very dense star formed from the core of a red giant, in which no fusion occurs

Planetary nebula

The outer layers of a red giant that have drifted off into space, leaving the hot core behind at the centre as a white dwarf

Electron degeneracy pressure

A quantum-mechanical pressure created by the electrons in the core of a collapsing star due to the Pauli exclusion principle

Chandrasekhar limit

The mass of a stars core beneath which the electron degeneracy pressure is sufficient to prevent gravitational collapse - 1.44 solar masses

Supernova

The implosion of a red supergiant at the end of its life, which leads to the subsequent ejection of stellar matter into space, leaving an inert remnant core

Neutron star

The remnant core of a massive star after the star has gone supernova and the core has collapsed under gravity to an extremely high density, as it is almost entirely made up of neutrons

Black hole

The remnant core of a massive star after it has gone supernova and the core has collapsed so far that in order to escape it an object would need an escape velocity greater than the speed of light, and therefore nothing can escape

Low mass stars stay on main sequence…

Much longer

What mass stars turn in to red giants?

Between 0.5 and 10 solar masses

If mass is greater than Chandrasekhar limit, after supernova it turns into…

Neutron star

If core has a mass greater than 3 solar masses…

Black hole is formed