Dismembered galaxy has 'last hurrah' of star birth

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Dismembered galaxy has 'last hurrah' of star birth

20:35 02 March 2007
NewScientist.com news service
David Shiga

A galaxy in the process of being dismembered has been imaged by the Hubble Space Telescope. The unfortunate victim is having its stars and gas stripped away as it plunges at great speed towards the centre of a massive galaxy cluster.

The galaxy has been nicknamed the 'Comet galaxy' because of its unusual shape, which includes a tail of stars and gas streaming out behind it. It was discovered in Hubble images of a galaxy cluster called Abell 2667 by a team of astronomers led by Luca Cortese of Cardiff University in the UK.

It is a spiral galaxy with about the same mass as our own Milky Way. But while the Milky Way resides in a relatively placid environment, the Comet galaxy is hurtling towards the core of a massive cluster of galaxies, drawn by the cluster's tremendous gravity.

The galaxy is being ripped apart by the pressure of hot gas within the cluster that it is speeding through, as well as so-called 'tidal' forces due to the uneven pull of the cluster's gravity on different parts of the galaxy.

Stagnant future
As a result of these forces, millions of stars are being flung off into intergalactic space. The galaxy is also losing the gas it would need to fuel future star formation, dooming it to a stagnant future as its stars age and few new ones are born.

Watch an animation illustrating the dismemberment process.

Even as the galaxy is being sterilised, it is having a last hurrah of star formation. The tidal forces have dislodged gas from the galaxy's outskirts and funnelled it to the galaxy's centre, where it has ignited a burst of star birth.

"In the midst of all this destruction, the cluster's strong forces have triggered a baby-boom of star formation," says team member Giovanni Covone of the Osservatorio Astronomico di Capodimonte in Naples, Italy.

The same process may help explain why there are more gas-poor galaxies dominated by old stars today than there were billions of years ago.

Journal reference: Monthly Notices of the Royal Astronomical Society (in press)

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