Alien Star System Buzzed the Sun

An alien star passed through our Solar System just 70,000 years ago, astronomers have announced. No other star is known to have approached this close to us.

An international team of researchers says it came five times closer than our current nearest stellar neighbour - Proxima Centauri.

The object, a red dwarf known as Scholz's star, cruised through the outer reaches of the Solar System - a region known as the Oort Cloud.

Scholz's star was not alone; it was accompanied on its travels by an object known as a brown dwarf. These are essentially failed stars that lacked the necessary mass to get fusion going in their cores.

The findings are published in Astrophysical Journal Letters.

Observations of the star's trajectory suggest that 70,000 years ago this cosmic infiltrator passed within 0.8 light years of the Sun. By comparison, Proxima Centauri is 4.2 light years away.

In the paper, astronomers led by Eric Mamajek at the University of Rochester, New York, say they are 98% certain that Scholz's star travelled through what is known as the "outer Oort Cloud" - a region at the edge of the Solar System filled with trillions of comets a mile or more across.

This region is like a spherical shell around the Solar System and may extend out to as much as 100,000 Astronomical Units, or AU (one AU is the distance between the Earth and the Sun).

The Oort Cloud is thought to give rise to long-period comets that can swing past the Sun when their orbits are disturbed.

To determine the trajectory of the star, the researchers needed two pieces of information: the change in distance from the Sun to the star (its radial velocity) and the star's motion across the sky (its tangential velocity).

Scholz's star currently lies 20 light years away - making it a fairly nearby system. But it showed very slow tangential motion for a star this close. This indicated that it was either moving away from us or towards a future close encounter with the Solar System.

The radial velocity measurements confirmed that the star system was actually speeding away from us. By tracing its movements back in time, they found that its close shave with the Sun occurred some 70,000 years ago. (BBC)