Baby supernova seen right in our neighborhood

By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters) - A baby supernova, just over a century old, has been found in the middle of our own Milky Way galaxy and provides an unprecedented opportunity to watch a star dying, astronomers said on Wednesday.

The supernova, known as G1.9+0.3, would have made a bright flash when it first exploded 140 years ago but was not seen because dust obscures it, David Green of Britain's University of Cambridge and colleagues reported.

"It's by far the youngest supernova identified in the galaxy," Green told reporters in a telephone briefing.

Green first identified the object in 1985 as a possible supernova, using radio readings from the U.S. National Science Foundation's Very Large Array.

In 2007, Stephen Reynolds of North Carolina State University and colleagues looked at it using the orbiting Chandra X-Ray Observatory. They were surprised to find it was 16 percent bigger than the radio measurements.

"The only reasonable explanation we could come up with was, in the 22 years between those observations, it had grown by that rate," Reynolds said.

They extrapolated its rate of growth to date the original explosion at 140 years ago.

The supernova is at the center of the galaxy, roughly 25,000 light-years from Earth. A light-year is the distance light travels in one year -- about 5.8 trillion miles.

Reynolds says the discovery renews the question of why so few supernovae have been seen in the Milky Way. Based on other galaxies, astronomers have estimated that about three such stellar explosions should occur every century.

The most recent supernova in Earth's neighborhood known until now occurred around 1680, creating the remnant called Cassiopeia A.

"If the supernova rate estimates are correct, there should be the remnants of about 10 supernova explosions in the Milky Way that are younger than Cassiopeia A," said Green.

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

Dust could be hiding most of them, Green and Reynolds said, but X-ray and radio observations might find them.

"Looking out of the Milky Way, 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 back yard," Reynolds said.

Writing in the Astrophysical Journal Letters and Monthly Notices of the Royal Astronomical Society, the researchers said they can now watch and analyze the explosion as it unfolds.