Scientists have discovered the most recent supernova in our galaxy, which they say would have been visible to the naked eye, had it not happened so close to the murky centre of the Milky Way.

Named G1.9+0.3, the supernova in the constellation Sagitarius is some 140 years old. It 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.

Experts hope it will allow them to learn more about stellar explosions, and about their effects on the surrounding area. 

"No other object in the galaxy has properties like this," said Stephen Reynolds of North Carolina State University in Raleigh, who led the study.

"This find is extremely important for learning more about how some stars explode and what happens in the aftermath."

Expanding remains

The 'new' supernova is about 200 years younger than Cassiopeia A, the last known Milky Way supernova that exploded around 1680.

It 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 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.

Age estimates are based on the rate of expansion of the supernova remains - the faster the expansion the more recent the explosion - and in the intervening 22 years, the remnants had expanded about 16 per cent, 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.

Bright gas cloud

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, and would probably have been taken for a new star.

"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," Mr Reynolds said.

"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."

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.

Neutron star

The explosion can also 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.


Source: AFP/SBS