A2 Physics Unit 2 Module 5

Front 1

Galaxy

Back 1

A large collection of stars orbiting its own centre of gravity.

Front 2

Nebulae

Back 2

A huge collection of mainly hydrogen gas forming a cloud-like structure in space.

Front 3

Main sequence star

Back 3

A star in the main phase of its life.

Front 4

Red giant

Back 4

A star in the later stages of its life that has nearly exhausted the hydrogen in its core. It therefore begins to fuse helium, cools and expands.

Front 5

White dwarf

Back 5

The end product of low mass stars when the outer layers have dispersed into space.

Front 6

Supernova

Back 6

A huge explosion caused when a large star collaspses in on itself.

Front 7

Neutron star

Back 7

The remains of the core of a large star after it has undergone a supernova . It is incredibly dense and is composed mainly of neutrons. Also known as a pulsar.

Front 8

Black hole

Back 8

The remains of the core of a very large star after it has gone supernova. It has an infinite density and a gravitational field strength so great that even light cannot escape.

Front 9

Hubble's law

Back 9

The speed of recession of a galaxy is directly proportional to its distance from the Earth.

Front 10

Cosmological principle

Back 10

On a large scale the universe is uniform( the universe is the same in all directions and of uniform density, provided a large enough volume is considered).

Front 11

Isotropic

Back 11

The same in all directions.

Front 12

Homogeneous galaxy

Back 12

Of uniform density

Front 13

Plasma

Back 13

A state in which protons and electrons are not bound to one another because the temperature is too high.

Front 14

Closed universe

Back 14

The situation if the mean density of the universe is greater than the critical density. The universe will collapse back into a single point(big crunch).

Front 15

Open universe

Back 15

The situation if the mean density of the universe is less than the critical density. The universe will continue to expand.

Front 16

Flat universe

Back 16

The situation if the mean density of the universe is equal to the critical density. The galaxies in the universe will slow down but never quite stop. This situation is very unlikely.