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Last Updated: Saturday, 20 November, 2004, 17:23 GMT
Nasa launches cosmic blast hunter
Delta launch (Boeing)
Swift is sent on its way (Image: Carleton Bailie/Boeing)
A new space observatory has been launched to hunt down and study the most powerful explosions seen in the Universe since the Big Bang itself.

The Swift satellite will detect and analyse gamma-ray bursts - very intense but fleeting flashes of radiation.

Scientists think they may signal the birth of black holes which are created when giant stars fall in on themselves.

Swift - a combined US, UK and Italian mission - was launched on a Delta rocket from Cape Canaveral in Florida.

The $250m observatory carries three instruments which work together.

The Burst Alert Telescope has been built by the US space agency's (Nasa) Goddard research centre to detect and locate a gamma-ray burst over a wide portion of the sky.

The information it provides will be used to swivel Swift directly at the burst position.

Quick response

It can then study the event with its X-ray Telescope (XRT), built by Penn State University, the University of Leicester and the Osservatorio Astronomico di Brera; and its UltraViolet/Optical Telescope (UVOT), made by Penn State and University College London's Mullard Space Science Laboratory.

Impression: Forming black hole exudes energetic jet (BBC)
In the formation of black holes, highly energetic jets are created
Speed is all important - as the name of the observatory suggests.

The gamma-ray event itself may last only a few seconds - although the afterglow that frequently follows a burst continues to emit X-rays, optical light and radio waves for hours or weeks afterwards.

Scientists have struggled to explain the power of these cataclysmic events. They pack more energy into their fleeting appearance than our Sun will release in its entire lifetime.

"The only way we can think of to produce such high luminosities is by making a black hole and that is our current best estimate of how these gamma-ray bursts are actually formed," said Professor Keith Mason, from the Mullard Space Science Laboratory and UK lead investigator for the UVOT on Swift.

Superfast jet

Theory suggests a giant short-lived star can experience a catastrophic collapse when the nuclear reactions in its core can no longer support its mass.

This type of star implodes, creating a black hole at its centre and sucking in all the material around it.

"This material spirals down into the black hole very quickly," Professor Mason told BBC News. "One of the consequences of this is that a high velocity jet is formed.

Swift, Nasa
Swift will investigate the source of gamma-ray bursts
"This jet is travelling at very close to the speed of light, and it punches its way out through the star, producing shocks which produce gamma-rays, which produce X-rays, which produce the flash that we see."

Scientists also think the bursts can form when two neutron stars collide. However, they are keeping their minds open to the possibility that other, hitherto unimagined, phenomena might cause the giant blasts.

Most are extremely distant, and scientists hope they can be used to peer back in time to understand the nature of the very first stars to shine in the Universe.

They will be keen to know, too, if the sorts of stars that give rise to gamma-ray bursts could exist nearby in our galaxy.

No Hope

"If an event were to occur relatively close to our position in our galaxy, the energy emission is so intense that you could envisage massive doses of gamma-ray radiation reaching the Earth's surface," said Professor Alan Wells, from the University of Leicester and UK lead investigator for the XRT.

"That would be very damaging to life as we know it and have a very serious effect on the preservation of the atmosphere around the Earth," he told the BBC.

Supernova remnant W49B (Chandra/Palomar - Nasa/CXC/SSC/J.Keohane et al)
Star wreckage W49B: 35,000 light-years from Earth and possible location of past burst
"Even if we survived that, the expectation is that following the gamma-rays there would be very high-energy particles - cosmic rays - which would arrive over a period of weeks and even months from which, to be honest, there is no escape," added Dr Nial Tanviar, from the University of Hertfordshire, who will use Swift data.

"These particles can penetrate quite deep underwater and into the ground, and so you can see how life on Earth would be in pretty serious trouble."

Gamma-ray bursts were first observed during the Cold War, when Western researchers thought that they might be the product of Soviet nuclear tests on the Moon or on other planets.

Swift will join four other satellites connected to a largely automated system that relays alerts on gamma-ray bursts in real time to scientists worldwide. This network will distribute Swift alerts via e-mail to scientists and to robotic telescopes.

Swift is a Nasa-led mission. "We expect to detect and analyse over 100 gamma-ray bursts a year," said Dr Neil Gehrels, Swift's Principal Investigator at Goddard.

"Swift will lead to a windfall of discovery on these most powerful explosions in the Universe."

Find out more about the Swift observatory

Gamma-ray burst mystery solved
16 Apr 03 |  Science/Nature
Scattered spacecraft pinpoint cosmic burst
18 Oct 00 |  Science/Nature
Space blast teaser
25 Mar 99 |  Science/Nature
Scientists snap deep space blast
28 Jan 99 |  Science/Nature

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