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New evidence on what triggered ancient Supernovas

April 27, 2011 - Washington

Using NASA's Chandra X-ray Observatory, astronomers have discovered new evidence on what trigged an historic supernova explosion.

The discovery also provides strong evidence that a star can survive the explosive impact generated when a companion star goes supernova.

The new study examined the remnant of a supernova observed by the Danish astronomer Tycho Brahe in 1572.

The object, dubbed Tycho for short, was formed by a Type Ia supernova, a category of stellar explosion useful in measuring astronomical distances because of their reliable brightness.

The researchers analyzed a deep Chandra observation of Tycho and found an arc of X-ray emission in the supernova remnant.

Evidence supports the conclusion that a shock wave created the arc when a white dwarf exploded and blew material off the surface of a nearby companion star.

"There has been an ongoing long-standing question about what causesype Ia supernovas," said Fangjun Lu of the Institute of High Energy Physics, Chinese Academy of Sciences in Beijing.

"Because they are used as steady beacons of light across vast distances, it is critical to understand what triggers them," he added.

Astronomers have two hypotheses for how Type 1a supernovas are sparked.

One is that two white dwarf stars merge together, and blow up in a cataclysmic blast that leaves no trace of either star.

The other is that a white dwarf pulls material from a "normal," or Sun-like, companion star until a thermonuclear explosion occurs.

The new observations, however, support the latter one.

In addition, the Tycho study seems to show the remarkable resiliency of stars, as the supernova explosion appears to have blasted very little material off the companion star.

Previously, studies with optical telescopes have revealed a star within the remnant that is moving much more quickly than its neighbors, hinting that it could be the missing companion.

"It looks like this companion star was right next to an extremely powerful explosion and it survived relatively unscathed," said Q. Daniel Wang of the University of Massachusetts in Amherst.

Using the properties of the X-ray arc and the candidate stellar companion, the team determined the orbital period and separation between the two stars in the binary system before the explosion.

Other details of the arc support the idea that it was blasted away from the companion star.

For example, the X-ray emission of the remnant shows an apparent "shadow" next to the arc, consistent with the blocking of debris from the explosion by the expanding cone of material stripped from the companion.

"This stripped stellar material was the missing piece of the puzzle for arguing that Tycho's supernova was triggered in a binary with a normal stellar companion. We now seem to have found this piece," said Lu.


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