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Last Updated: Monday, 13 September, 2004, 11:45 GMT 12:45 UK
Astronomers capture galactic dance
By Dr David Whitehouse
BBC News Online science editor

NGC 7320 - at the top-centre - could be much closer

Astronomers have released a stunning image taken by the Gemini Observatory of a cluster of interacting galaxies some 300 million light-years away.

The galaxies are members of a famous group called Stephan's Quintet. Their shapes are distorted by gravitational interactions that scatter arches of gas and dust through space.

Another result of this interaction is a prolific fireworks display of star formation, which is fuelled by clouds of hydrogen that have been forced into clumps to form stellar nurseries.

The unprecedented image of the cluster comes from a unique combination of sensitivity, high-resolution and field of view.

"It doesn't take long to reach an incredible depth when you have an 8-metre mirror collecting light under excellent conditions," says Travis Rector, of the University of Alaska, US, who helped obtain the data with the Gemini North Telescope on Mauna Kea, Hawaii.

"We were able to capture these galaxies at many different wavelengths or colours. This allowed us to bring out some remarkable details in the final colour image that have never been seen before in one view."

The clarity of the image is thanks, in part, to an instrument built in the UK, the Gemini Multi-Object Spectrograph (GMOS).

The instrument, which was built as a joint partnership between the UK Astronomy Technology Centre, University of Durham and the Hertzberg Institute of Astrophysics in Canada, is capable of obtaining hundreds of spectra in a single "snapshot" - enabling the study of galaxies at vast distances, as well as delivering high resolution images of this nature.

Dr Adrian Russell, director of the UK ATC, said: "This particular image demonstrates the exquisite detail that can be achieved when you use state-of-the-art instrumentation to exploit an 8-metre class telescope on a great site."

Foreground galaxy

Astronomers say that one striking element of the image is a group of red clumps that mark star-forming regions within a galaxy called NGC 7320.

The exact status of NGC 7320 and its relation to the others in the cluster is contested. However, most astronomers believe that the galaxy lies in the foreground, isolated from the more distant galaxies.

Observations show that NGC 7320 has an apparent velocity away from us of about 800km per second. In contrast, the rest of the group is being carried away from us by the expansion of the universe at over 6,000km per second.

Using current models for the expanding universe, this would put the bulk of the cluster almost eight times further away from Earth than NGC 7320.

Eventually, the galaxies in the cluster will lose their current identity, combining into even fewer objects than we see today.




SEE ALSO:
Hubble solves cosmic mystery
27 Oct 00  |  Science/Nature
Telescopes catch-up with Hubble
02 Jul 03  |  Science/Nature
Violent galaxy seen in 3D
15 Sep 04  |  Science/Nature


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