Cambridge Cosmology: Galaxies

Our own Galaxy - the Milky Way

Our own galaxy consists of about 200 billion stars, with our own Sun being a fairly typical specimen. It is a fairly large spiral galaxy and it has three main components: a disk, in which the solar system resides, a central bulge at the core, and an all encompassing halo.

The spiral galaxy M83 which is believed to be similar in size and shape to the Milky Way (AAO)

Disk:

The disk of the Milky Way has four spiral arms and it is approximately 300pc thick and 30kpc in diameter. It is made up predominantly of Population I stars which tend to be blue and are reasonably young, spanning an age range between a million and ten billion years.

Bulge:

The bulge, at the centre of the galaxy, is a flattened spheroid of dimension 1kpc by 6kpc. This is a high density region where Population II stars predominate---stars which tend toward red and are very old, about 10 billion years. There is growing evidence for a very massive black hole at its centre.

Halo:

The halo, which is a diffuse spherical region, surrounds the disk. It has a low density of old stars mainly in globular clusters (these consist of between 10,000 - 1,000,000 stars).The halo is believed to be composed mainly of dark matter which may extend well beyond the edge of the disk.

A view of the Milky Way from the southern hemisphere - towards the centre of our galaxy (AAO)

[Back][Hot big bang][Galaxies][Relic radiation][Cosmic strings][Inflation][Cosmology][Next]