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Stellar surprises

07 May 2010

The cloud of gas and dust called RCW120, courtesy of ESA/PACS/SPIRE/HOBYS ConsortiaThe cloud of gas and dust called RCW120, courtesy of ESA/PACS/SPIRE/HOBYS Consortia

Previously unseen star formation has been revealed in the first scientific results from the Herschel infrared space observatory.

Herschel is the largest astronomical telescope ever to be placed into space and the SPIRE instrument onboard was built by an international consortium, led by the School of Physics and Astronomy.

The new images show thousands of distant galaxies furiously building stars and one picture catches an ‘impossible’ star in the act of formation. The findings challenge old ideas of star birth and were presented during a major scientific symposium held at the European Space Agency (ESA), attended by leading academics from the School.

Herschel’s observation of a cloud of gas and dust, called RCW120 has revealed an embryonic star which looks set to turn into one of the biggest and brightest stars in our Galaxy within the next few hundred thousand years. The very young star already weighs in at around ten times the mass of the Sun, and can continue to grow by feeding on the surrounding cloud, which still contains about 200 times as much material as the star.

Current theories suggest that the fierce light emitted by such large stars should blast away their birth clouds before they grow any larger than around ten times the mass of the Sun. Despite this, many of these ‘impossible’ stars are already known, some up to 150 times the mass of the Sun.

"The fact that stars like this exist at all is one of the biggest mysteries in astronomy, and this star is probably going to be huge", said Professor Derek Ward-Thompson of the School of Physics and Astronomy. "Now that we’ve seen such a young example, we can start to investigate why our theories can’t explain its existence". Professor Ward-Thompson is part of the Herschel imaging survey of OB Young Stellar objects (HOBYS) programme led by SAp/CEA, Saclay, France.

Thousands of galaxies were captured by HerschelThousands of galaxies were captured by Herschel

Herschel has also been measuring the infrared light from thousands of other galaxies, spread across billions of light-years. Each galaxy appears as just a pinprick but its brightness allows astronomers to determine how quickly it is forming stars. Roughly speaking, the brighter the galaxy the more stars it is forming.

Until now, astronomers believed that galaxies have been forming stars at about the same rate for the last three billion years. Herschel shows this is not true, finding that galaxies have been changing over cosmic time much faster than previously thought.

These findings will be examined as part of the largest Herschel project, called Herschel ATLAS which will let astronomers investigate the reasons for this behaviour.

Investigating the evolution of galaxies is just one of the science projects that Herschel ATLAS will carry out. This survey will cover one eightieth of the sky, four times larger than all the other Herschel surveys combined.

Professor Steve Eales, of the School of Physics and Astronomy who will lead the ATLAS programme, along with Nottingham University said: "Every time astronomers have observed the universe in a new waveband, they have discovered something new. So as well as our regular science programmes, I am hoping for the unexpected."

These are just two of the many discoveries presented this week at the Herschel First Results Symposium, ESLAB 2010, held at the European Space Research and Technology Centre, Noordwijk, the Netherlands where many Cardiff astronomers are presenting their results, due to be published in a special issue of the journal Astronomy & Astrophysics.

Speaking about the symposium, Professor Matt Griffin of the School, who leads the international team responsible for the Herschel-SPIRE instrument, said: "At this meeting we are seeing how Herschel is making now discoveries across the whole range of astronomy, from the solar system to the most distant galaxies. That’s very satisfying for those who worked for so long to build the observatory and its instruments."

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