Astronomers spot Milky Way's youngest supernova

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WASHINGTON (AFP) - Astronomers have discovered the most recent supernova in our Milky Way, hoping it will further knowledge about the spectacular stellar explosions and the workings of our galaxy, a research paper said Wednesday.

Named G1.9+0.3, the supernova in the constellation Sagitarius is some 140 years old and was detected through radio and X-ray telescopes, since the original, dazzling explosion was hidden from view by a dense field of gas and dust near the galaxy center, where it took place.

It is about 200 years younger than Cassiopeia A, the last known Milky Way supernova that exploded around 1680. Age estimates are based on the rate of expansion of the supernova remains -- the faster the expansion the more recent the explosion.

Stephen Reynolds of North Carolina State University in Raleigh, who led the study, said the new supernova was first noticed by astronomers more than 20 years ago, when the original explosion was estimated to have happened 400-1,000 years ago.

Its more recent origin became apparent, he said, when images of the object taken in 2007 through NASA's Chandra X-ray Observatory were compared with the 1985 images of the National Radio Astronomy Observatory's Very Large Array, which also belongs to NASA.

In the intervening 22 years, Reynolds said, the supernova remnants had expanded about 16 percent, indicating that they were much younger than previously thought.

Measurements taken earlier this year by the Very Large Array confirmed the age of the supernova remains at 140 years, possibly less if the expansion has been slowing down, making it the youngest on record in the Milky Way, the astrophysicist said.

With an unobstructed view, had the supernova not taken place near the center of the galaxy, the stellar explosion would have been visible in 1870-1900 in Sagittarius and probably taken for a new star, he explained.

"We can see some supernova explosions with optical telescopes across half of the universe, but when they're in this murk we can miss them in our own cosmic backyard," Reynolds said in a telephone press conference.

"Fortunately, the expanding gas cloud from the explosion shines brightly in radio waves and X-rays for thousands of years. X-ray and radio telescopes can see through all that obscuration and show us what we've been missing."

He said astronomers normally observe ancient supernova remnants with small rates in expansion that are very difficult to measure.

The remains of the galaxy's most recent supernova are very brilliant and should afford astronomers keener insight into the phenomenon and its effects on the surrounding galaxy, Reynolds said.

"No other object in the galaxy has properties like this," he said. "This find is extremely important for learning more about how some stars explode and what happens in the aftermath."

Supernovae occur when stars run out of nuclear fuel and explode, providing crucial information about the universe's history.

They heat and redistribute large amounts of gas, and pump heavy elements out into their surroundings and can trigger the formation of new stars as part of a cycle of stellar death and rebirth.

The explosion also can leave behind, in addition to the expanding remnant, a central neutron star or black hole.

A rare occurrence in the span of a human lifetime, supernovae are estimated to happen about three times per century in the Milky Way.

"If the supernova rate estimates are correct, there should be the remnants of about 10 supernova explosions that are younger than Cassiopeia A," said David Green of the University of Cambridge in the United Kingdom, who led the Very Large Array study.

"It's great to finally track one of them down."

The study is published in the January 10 issue of The Astrophysical Journal Letters.