June 13, 2008

Researchers Witness First Flash of a Dying Star

Scientists on Thursday were given a unique glimpse into how a supernova forms when they witnessed, for the first time, the flash of light produced inside a dying star just before it explodes.

The astronomers said the red supergiant, more than 500 times more massive than the Earth's own sun, was destroyed after its core collapsed and a deadly shock wave of energy completely blew it up.

This marks the first time that scientists have been able to observe the afterglow of a burst while knowing which star in the galaxy exploded.

"We have witnessed the violent death of a massive star in a galaxy almost one billion light years away in unprecedented detail," Kevin Schawinski, an astronomer at the University of Oxford who led the study.

"We caught the star while the supernova shock wave approached the surface of the star and then blew it apart."

A light year is the distance light travels in a year.

Images from a satellite pointed to where telescopes on Earth had detected supernovae"”which are created by the explosion of a star. They expected a first flash from inside a dying star to only be visible in ultraviolet light from space.

Stephen Justham, a University of Oxford astronomer who worked on the study, said after the satellite produced images of a seven-hour flash, the researchers sifted through data taken from telescopes in Hawaii fixed to the same coordinates that later confirmed a supernova formed in that precise location.

Justham said the flash began just hours before the star was disrupted.

"How the shock wave travels in a star tells us the size of the star and what the inside is like in its final moments. The longer the flash, the bigger the star."

The researchers said understanding what happens inside a star is important because the core normally acts as a powerful nuclear furnace producing heat and pressure that makes the star shine and remain stable for a long time.

The cores of these big stars collapse when they run out of fuel and can spark a shock wave that travels to the surface at 20 million miles per hour to create a fireball one billion times brighter than the sun.

The researchers said that supernovae are hurtling fields of heavy material that spew nickel, gold and iron, so understanding more about them can also provide insight into the formation of Earth.

The Earth's sun is smaller so when it reaches the end of its life in about 4 billion years it will bloat and then shed its outer layers, leaving the remains to cool over a long period of time.

Schawinski said most of the heavy elements on Earth were made up from the inside of stars. "If there hadn't been supernovae that created all these heavy elements in the distant past before the sun was formed there wouldn't have been the raw materials to form earth."

The research was reported in the journal Science.


Image Caption: Flash of ultraviolet light revealing the death throes of a star. Credit: Kevin Schawinski (Oxford), NASA/GALEX/HST, COSMOS


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