Youngest supernova is 140 years old

May 14, 2008 1:31:22 PM PDT
Astronomers have discovered the youngest known supernova in the Milky Way galaxy, still just a baby at 140 years old. The scientists, who announced their findings Wednesday, used a radio observatory in New Mexico and NASA's Chandra X-ray Observatory in space to identify when the supernova, or stellar, explosion occurred. They put the star-dying event at sometime around 1868.

Before this, the youngest supernova in the Milky Way was thought to have occurred around 1680.

A supernova is the catastrophic explosion of a star that releases an extraordinary amount of energy, enough to outshine an entire galaxy.

This new baby supernova is located near the center of the galaxy and obscured by dense gas and dust, making it virtually impossible to see in optical light.

Two to three supernovae are thought to occur every century in the Milky Way. As a result, there are probably even younger ones out there waiting to be identified, said David Green of the University of Cambridge in England, who led the radio observatory study.

Green and others have been tracking the remnant of this supernova since 1985 via the National Science Foundation's Very Large Array, a radio astronomy observatory. But it wasn't until last year that a team led by North Carolina State University physicist Stephen Reynolds found with help from Chandra how much the remnant had expanded. That indicated the supernova was much younger than initial estimates ranging from 400 to 1,000 years old.

The Very Large Array made new observations in March and helped pinpoint the age at 140 years, possibly less if the expansion has been slowing.

"It's the combination of the radio and the X-ray, the older technique and the new one, that tells us what this object really is. So you get a lot more when you put all of these clues together," said Robert Kirshner, a Harvard University astronomer who is not affiliated with the study.

"It's a little like one of those shows on TV where they investigate a death. This is a stellar death, all right, and the corpse is still warm," Kirshner said during a teleconference with reporters.

Astronomers typically observe supernova remnants that are 10,000 or so years old, not relative infants like this one. Getting the total picture, from the start, is important in figuring out how often supernovae explode in the Milky Way.

In this case, "you're actually getting to see the rock that made the splash, not the wave that's going out into the pond," Kirshner said.

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