Astronomers have discovered a pair of stars that go round each other in less than five and a half minutes.

The pair, known as a binary star, has the name of HM Cancri. It is the smallest known binary star, and also has the shortest known orbital period (the time it takes for the stars to revolve around each other).

HM Cancri is almost 16,000 light years from Earth and is made up of two white dwarf stars. These were stars similar to our sun, but have run out of fuel and collapsed in on themselves due to the force of gravity.

These two white dwarfs are so close that material is actually travelling from one to the other. It is a very unusual example, and astronomers hope that it could help to answer some questions about how gravity works.

Image by Rob Hynes