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Orbiting Telescope Linked to Cambridge Finds Young Supernova

Orbiting Telescope Linked to Cambridge Finds Young Supernova

By Karen Klinger

Using an orbiting X-ray telescope whose day-to-day science and flight operations are controlled by the Smithsonian Astrophysical Observatory in Cambridge, researchers have discovered the youngest known supernova in the Milky Way--a star that exploded near the center of our galaxy about 140 years ago.

The scientists, who announced the finding May 14, used NASA's Chandra X-ray Observatory, along with a radio array observatory in New Mexico, to identify the remnants of the star dubbed G1.9. Previously, the most recent known stellar explosion in the Milky Way was thought to have occurred around 1680.

Although the earlier explosion of the star Cassiopeia A may have been visible from Earth, scientists said the death of G1.9 could not be detected in optical light because it was obscured by dense clouds of dust and gas. In other words, as spectacular as the explosion might have been, no one living then could see it.

Stephen Reynolds of North Carolina State University, who led the Chandra team, said that while optical telescopes can observe supernova explosions even halfway across the universe, "when they are in this murk, we can miss them in our own backyard." But X-ray and radio telescopes "can see through all that obscuration and show us what we've been missing."

Researchers using the radio telescope array in New Mexico first detected the remnants of G1.9 in 1985, but estimated that it could be 400 to 1,000 years old--making it about as old or older than the Cassiopeia supernova. It wasn't until they used Chandra, the world's most powerful X-ray telescope, to track its rapid rate of expansion that they discovered it was much younger than previously thought. The Chandra findings were confirmed with new data from the radio array within just the past few weeks.

In a teleconference with reporters, Harvard University astronomer Robert Kirshner said "self-interest" is one reason for studying stellar explosions because "the calcium that's in your bones and the iron that's in your blood probably came from supernovae that exploded before the sun was formed. So, we're all stardust, and it seems reasonable for us to want to know how these elements get formed when stars explode."

Most known supernovae remnants are at least 10,000 years old and "there you are seeing the glowing shock wave going out into the gas between the stars, but you don't see the actual shredded star. With young objects like this one (G1.9), you're actually getting to see the rock that made the splash, not the wave going into the pond," said Kirshner, the associate director of the Harvard-Smithsonian Center for Astrophysics, which includes the Smithsonian observatory.

He said what made the discovery possible was the inspired decision to coordinate the observations of the decades-old radio observatory with the cutting-edge technology of the Chandra telescope. Launched by the space shuttle in 1999, Chandra is 25 times sharper than the best previous X-ray telescopes and allows scientists to track cosmic events through clouds of hot gas stretching millions of light years across the universe.

It is the "combination of the radio and the X-ray--the older technique and the new one--that tells us what this object (G1.9) really is. So you get a lot more when you put all of these clues together," Kirshner said. "It's a little like one of those shows on television where they investigate a death. This is a stellar death, and the corpse is still warm."

NASA Photo Credits: Supernova remnant G1.9 composite image made by Chandra X-ray Observatory and Very Large Array radio image (X-ray: NASA/CXC/Reynolds et al; Radio: NSF/NRAO/VLA/Cambridge/D.Green et al); Artists's impression looking down on the Milky Way with G1.9 position in black (NASA/CXC/M.Weiss); Artist's impression of supernova explosion resulting in the formation of G1.9 (NASA/CXC/M.Weiss)