By Dr David Whitehouse BBC News Online science editor

The new star was found because its relatively swift motion across the sky was picked up by automated sky surveys.

It ranks as the third closest star system and the fifth closest star to our Sun.

It is a faint red star, a so-called red dwarf, and is only 7.5 light years away.

A dim red dwarf star (Nasa/Esa)

As yet unnamed the new star goes by the designation SO025300.5+165258.

It is the closest star system to us after the Alpha Centauri system and Barnard's star.

The discovery was made by searching databases of star images recorded by automated sky surveys.

Such surveys are undertaken to look for comets and asteroids as well as exploding stars.

Because they are regular snapshots of regions of the sky they are also useful for finding nearby stars.

Red dwarf

Nearby stars betray their presence through having a large 'proper motion' - that is their natural motion through space, although no greater than most stars, is more pronounced because of their closeness.

When the new star was detected it was subsequently found in photographs going back half a century.

It is a small dim red dwarf star, nothing unusual in cosmic terms, one of the common folk of the galaxy.

But measurements do indicate that it is one of the closest ever found to our Sun.

The researchers who found it, an international team led by Bonnard Teegarden of the American space agency (Nasa), say that other nearby stars are surely waiting to be discovered.