Star formation may jump from place to place inside a galaxy like a bushfire front, according to a team of astronomers from the UK, Australia and Spain. The team used the Hubble Space Telescope and other telescopes to study a galaxy called NGC 2903, which lies 25 million light-years away and is similar to our own galaxy. The HST picture shows that known 'hot spots' near the centre of the galaxy are clusters of stars born 5 to 10 million years ago. Other spots in the galaxy are clouds of ionised hydrogen gas where young stars are forming today. The two kinds of spots are far apart, meaning that star-forming activity is shifting from place to place. "It's moving surprisingly fast, about a million kilometres a year on average," says team member Dr Stuart Ryder of the Anglo-Australian Observatory in Sydney. Stars form when a giant cloud of cold hydrogen gas collapses in on itself. "Star formation may be like a bushfire," says Dr Ryder. "Once it has burnt out an area, it has to move on to where there's more fuel, or it will die out." "Perhaps when one cloud of gas is used up by being turned into stars, the star-forming process starts in a neighbouring cloud, possibly triggered by shock waves from stars exploding nearby." The astronomers also found that a dense region of stars in the galaxy, called a bar, seems to funnel gas into the galaxy's centre, fuelling the birth of young stars. "The centre of this galaxy is like a retirement village," Dr Ryder says. "Most of the stars are old. But we see a bit more action in places - a couple of discos starting up. That means there are some younger inhabitants as well." The research team members are Almudena Alonso-Herrero (University of Hertfordshire, UK), Stuart D. Ryder (Anglo-Australian Observatory, Sydney, Australia) and Johan H. Knapen (Isaac Newton Group of Telescopes, Spain and the University of Hertfordshire, UK).
