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Exploding star
10 April 2006What happens when stars go bang?
Astronomers from Liverpool and around the world have been able to watch a star explode in unprecedented detail, using an armada of telescopes on the ground and in space, giving them unrivalled new evidence of what happens "when stars go bang".
Mike Bode, LJMU's Professor of Astrophysics, presented findings on the explosion, alongside Dr Tim O'Brien of Jodrell Bank Observatory, at the National Astronomy Meeting of leading astronomers in Leicester on Friday 7 April.
The findings received media coverage around the world, including on the BBC website, http://news.bbc.co.uk/2/hi/science/nature/4885700.stm. To see a movie depicting a nova outburst similar to the RS Ophiuchi system, where a white dwarf (centre), which has steadily been accreting material from a red giant companion, undergoes a thermonuclear explosion on its surface, click here.
Professor Bode explained the importance of the explosion saying: "Like the Sun, most stars in the Universe end their days with a whimper, but a few literally go out with a bang. Among these are the supernovae and their even more energetic cousins known as Gamma Ray Bursters (GRBs). The latter are the largest explosions since the Big Bang itself, and we now think that most GRBs are due to the collapse of stars over 30 times the mass of the Sun in a so-called 'hypernova' explosion".
He continued: "What makes the star we have just seen explode so important is that although it is not a supernova or hypernova, it is close enough to study in great detail and we also know a great deal about what it was like before it exploded. What's more, the remnant of a supernova or hypernova explosion takes around 10,000 years to go through all its phases, whereas the star we are studying is evolving right before our eyes. It will help us better understand those catastrophic cosmic explosions that are responsible, among other things, for the origins and distribution of many of the vital elements that make up not only the heavenly bodies but also our own."
The star, a so-called 'recurrent nova' known as RS Ophiuchi, is about 5,000 light years from Earth and it exploded with such ferocity and power that it was clearly visible in the night sky without the aid of a telescope. In just one day, the star emitted more energy than the Sun does in several centuries and expelled several times the mass of Earth in hydrogen-rich gases at speeds of several thousand km per second.
It's not the first time that the star has been seen to explode - the first was recorded in 1898 and the last time was as recently as 1985 - but this time telescope technology was advanced enough to respond to the outburst extremely rapidly and capture the explosion in minute detail. An array of space and ground-based telescopes has been recording the explosion since amateur astronomers alerted the international professional astronomical community on February 12th, and more data are arriving every day.
RS Ophiuchi is in fact a binary star system comprising a super-dense star known as a white dwarf, about the size of the Earth, which is in orbit with a far larger red giant star. The two stars are so close together that the outer layers of the red giant are continuously being pulled onto the smaller dwarf star by its high gravity. Every 20 years or so, the dwarf star accumulates enough gas that a runaway thermonuclear explosion occurs on its surface.
Within hours of notification of RS Ophiuchi's latest outburst being relayed to the international astronomical community, telescopes both on the ground and in space swung into action. Among these is NASA's Swift satellite which, as its name suggests, can be used to react rapidly to things that change in the sky, and began observing the star just three days after its outburst began.
"We realised from the few X-ray measurements taken late in the last outburst that this was an important part of the spectrum in which to observe RS Ophiuchi as soon as possible," said Professor Bode, who led the observing campaign for the 1985 outburst and now heads the Swift follow-up team on the current explosion.
Radio telescopes in Europe, North America and Asia are now monitoring the star very closely and optical observations are also being obtained by many observatories around the globe, including LJMU's robotic Liverpool Telescope on La Palma. Observations are also being conducted at the longer wavelengths of the infrared part of the spectrum.
"In the 2006 outburst, we have a unique opportunity of understanding much more fully such things as runaway thermonuclear explosions and the end-points of the evolution of stars," said Professor Bode. "With the observational tools now at our disposal, our efforts 21 years ago look rather primitive by comparison."
Illustration: Artist's impression of the recurrent nova RS exploding 5,000 light years from Earth.
Credit: David A. Hardy (www.astroart.org/) & PPARC.
Movie credit: Dr Andrew Beardmore, University of Leicester.
