Black Holes

- Describe the nature of ... black holes
- Describe how astronomers obtain evidence for the existence of ... black holes.

No astronomer has ever seen a black hole, largely because there is too much material surrounding it and also because it is black as the name suggests.

Most astronomers accept they exist but there is a lot about them that we don't know.

When a very large star explodes, the mass condenses so much that is collapses in on itself. The gravity is still present.

It appears to pull in any material in the vicinity. Once matter goes past the boundary of a black hole (called the event horizon) it cannot escape back out again; not even light can escape which travels at 300,000 kilometres a second.

Evidence from black holes comes from binary stars that get their solar material pulled into the hole. This often forms an accretion disc of matter circling the area. It orbits so fast it is hot enough to give off x-rays which we can measure.

The black hole forces such a gravitational force on these particles it can push them light years away, perpendicular to the disc in the form of particle jets travelling near to the speed of light.

It is thought that most galaxies have a super massive black hole in their centre.


Animation New Window

Star Evolution animation Star Life

Image New Window

Black Hole in the nucleus of the Whirlpool Galaxy

Links New Window

Imagine the Universe Ask an Astrophysicist: Black Holes

Imagine the Universe Black Holes

How Stuff Works Black Holes


  • What are black holes?
  • How are they formed?
  • What evidence is there for their existence?
  • Name a common area in which to find them.