Supernova remnant: The expanding remains of G1.9+0.3. The original explosion was not seen in visible light because a dense field of gas and dust made it a trillion times fainter than if it had been unobscured. X-rays and radio waves from the resulting supernova remnant easily penetrate the field and allow us to capture an image.
Credit: X-ray (NASA/CXC/NCSU/S.Reynolds et al.); Radio (NSF/NRAO/VLA/Cambridge/D.Green et al.); Infrared (2MASS/UMass/IPAC-Caltech/NASA/
WASHINGTON DC: Astronomers have captured images of the most recent supernova in our galaxy. They hope the data will further knowledge about these spectacular stellar explosions and the workings of the Milky Way.
Named 'G1.9+0.3', the supernova in the constellation Sagittarius is some 140 years old and was detected through radio and X-ray telescopes. Visible light from the original, dazzling explosion has been hidden from view by a dense field of gas and dust near the galactic centre, where it took place.
Rate of expansion
It is about 200 years younger than Cassiopeia A, the previous most recent known supernova in the Milky Way, which exploded around 1680. Age estimates are based on the rate of expansion of supernovae remains – the faster the expansion the more recent the explosion.
Stephen Reynolds of North Carolina State University in Raleigh, U.S. – who led the team that report the discovery in an upcoming Astrophysical Journal Letters – said the new supernova was first noticed by astronomers more than 20 years ago, though the original explosion was estimated to have happened 400 to 1,000 years ago.
The fact that it was such a recent explosion only 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 per cent, indicating that they were much younger than previously thought.
The materials surrounding it are still expanding at almost 35 million miles per hour, said NASA, an unprecedented speed for a supernova remnant.
Buried in space muck
Measurements taken earlier this year by the Very Large Array radio astronomy observatory in New Mexico, U.S., confirmed the age of the supernova remains at 140 years, possibly less if the expansion has been slowing down.
Had the supernova not taken place near the centre of the galaxy, where its view was obstructed, the stellar explosion would have been visible from around 1870 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," said Reynolds. "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.
Brilliant insights
"No other object in the galaxy has properties like this," said Reynolds. "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 U.K., who led the Very Large Array part of the study. "It's great to finally track one of them down."
