Tuesday, April 26, 2011

Ancient Supernova Triggered by Stellar Cannibal

Ancient Supernova Triggered by Stellar Cannibal: "

An ordinary star may have lived through a catastrophic explosion that created one of the most famous supernova remnants in astronomy. A new look at the cosmic debris cloud known as Tycho’s supernova remnant shows an arc of material that could explain what creates a key type of supernova.

“It looks like this companion star was right next to an extremely powerful explosion and it survived relatively unscathed,” said astronomer Q. Daniel Wang of the University of Massachusetts in Amherst in a press release. The study appears in the May 1 Astrophysical Journal.

The remnant is named for the great Danish astronomer Tycho Brahe, infamously known for his metal nose and more respectably for describing in 1572 the stellar explosion that bears his name. It was formed by a Type 1a supernova, which are useful in measuring astronomical distances because of their reliable brightness. Type 1a supernovas have also been used to show that the universe’s expansion is accelerating, and to probe the mysterious force called dark energy that’s pushing the universe apart.

Astronomers have two hypotheses for how Type 1a supernovas are sparked. One is that two dense white dwarf stars merge together, and blow up in a cataclysmic blast that leaves no trace of either star. The other is that one white dwarf lives close to an ordinary, sun-like companion star, and steals material from the companion until it explodes. In that case, some bits of the companion might survive.

The new observations of Tycho, made with the Chandra X-Ray Observatory, support the idea of a battered companion. The material that showed up in X-ray images was probably blasted off the companion star in the explosion and shaped into an arc by a shock wave. A dark shadow next to the arc may have been sheltered from the blast.

Previous images with optical telescopes showed a fast-moving star within the remnant that could be the missing companion.

“This stripped stellar material was the missing piece of the puzzle for arguing that Tycho’s supernova was triggered in a binary [system] with a normal stellar companion,” said astronomer Fangjun Lu of the Chinese Academy of Sciences in Beijing in a release. “We now seem to have found this piece.”

Working backward from the X-ray data and the current position of the possible companion star, the astronomers calculated that the star originally sat only 9 million miles from the doomed white dwarf — less than a tenth the distance from the Earth to the sun.

Images: NASA/CXC/Chinese Academy of Sciences/F. Lu et al


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