Astronomers find 'cosmic vagabonds'

By Dr David Whitehouse
BBC News Online science editor

Astronomers have discovered clusters of stars drifting in what was thought to be the empty space between the galaxies.

Alone and drifting in-between the galaxies

The stars have been torn from their parent galaxies, and scattered into the intergalactic voids by gravity from other, passing galaxies.

Finding these cosmic "orphans" has pressed the capabilities of telescopes to their limits.

The scientists responsible have presented their work to the International Astronomical Union's (IAU) General Assembly in Sydney, Australia.

Droplets in space

Astronomers have known for more than a century that galaxies are surrounded by a swarm of ancient star clusters. Our own Milky Way galaxy has about 150 of these "globular clusters".

These clusters are no longer held within the gravitational grip of galaxies, and seem to be wandering freely through intergalactic space like cosmic vagabonds Dr Michael West, University of Hawaii

Globular clusters look like a droplet in space and can contain up to a million stars. Studies of them have provided many important insights into the formation of stars and galaxies.

Observations made by the Hubble Space Telescope and the giant 10-metre Keck Telescope on Mauna Kea, Hawaii, found the orphaned globular clusters.

Cosmic spill

"These clusters are no longer held within the gravitational grip of galaxies, and seem to be wandering freely through intergalactic space like cosmic vagabonds," says Dr Michael West of the University of Hawaii.

What it might look like up close

According to West, these globular star clusters probably once resided in galaxies just like most of the normal globular clusters that we see in nearby galaxies today.

However, the pull of gravity from a passing galaxy can rip stars and star clusters loose. In some cases, entire galaxies can be disrupted or destroyed by the gravitational pull from galactic neighbours.

It is thought that the partial or complete destruction of their parent galaxies spilled the globular star clusters into intergalactic space.