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Baby supernova in Milky Way
15/05/2008 08:04 - (SA)
Washington - 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.
Green first identified the object in 1985 as a possible
supernova, using radio readings from the US 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% 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.
At the centre of the galaxy
The supernova is at the centre of the galaxy, roughly
25 000 light-years from Earth. A light-year is the distance
light travels in one year - about 9.5 trillion kilometres.
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 neighbourhood 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.
'We are all stardust'
Writing in the Astrophysical Journal Letters and Monthly
Notices of the Royal Astronomical Society, the researchers said
they can now watch and analyse the explosion as it unfolds.
While more distant supernovae can be seen with the naked
eye, they quickly fade and the radio waves they create will
take centuries to arrive.
Dr Robert Kirshner of the Harvard Smithsonian Centre for
Astrophysics, who did not work on the study, said studying a
young supernova could help scientists understand the very
beginnings of life.
"The supernova makes a chemical element through real
alchemy - transforming one element into another one," Kirshner
said.
The iron in blood, for instance, was made by a star.
"We are all stardust and it seems reasonable for us to want
to know how these elements get formed when stars explode,"
Kirshner added.
"Our planet, our cells, our pieces are made of the vanished
ashes of these exploded supernovae ... You are actually getting
to see the rock that made the splash, not the wave that is
going out into the pond."
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