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Supernova Birth Observed for First Time - updated at 17:26 GMT, Wednesday, 21
May 2008 18:26




By Andrea Thompson Galaxy NGC 2770 before supernova SN 2008D exploded. An X-ray
image is on the left; the right is in visible light.

Exploding star caught in the act Supernova Birth Observed for First Time

NASA/Swift Science Team/Stefan Immler
Galaxy NGC 2770 before supernova SN 2008D exploded. An X-ray image is on the
left; the right is in visible light.


While peering at her computer screen four months ago, astronomer Alicia
Soderberg expected to see the small glowing smudge of a month-old supernova.
But what she and her colleague saw instead was a strange, extremely bright,
five-minute burst of X-rays.
With that observation, they became the first astronomers to catch a star in the
act of exploding.
'For years we have dreamed of seeing a star just as it was exploding, but
actually finding one is a once-in-a-lifetime, event,' said Soderberg, a Hubble
and Carnegie Princeton Fellow at Princeton University.
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The discovery, detailed in the May 22 issue of the journal Nature, will shed
light on the early stages of this violent stellar death, acting as a deciphering
key or 'Rosetta Stone' for supernova studies, as Soderberg puts it.

And analysis of the energy emitted by the new supernova, dubbed SN 2008D, could
help astronomers better understand this explosive process and the properties of
the stars that lead to it.
X-ray 'breakout'
A typical supernova occurs when the core of a massive star runs out of nuclear
fuel and collapses under its own gravity to form an ultradense object known as a
neutron star.
But only so much material can compress into the neutron star, so some of the
original star's collapsing gaseous outer layers can't fit; instead, they simply
bounce off the neutron star, Soderberg explained, triggering a shock wave that
plows back through the outer layers and blows the star to smithereens.
Astronomers had predicted for decades that this 'breakout' phase would produce
an X-ray blast lasting several minutes, but until Soderberg and Princeton
postdoctoral researcher Edo Berger's discovery, no one had ever observed the
signal. Supernovas were only found as they brightened days or weeks after their
initial explosion.
'Using the most powerful radio, optical and X-ray telescopes on the ground and
in space, we were eventually able to observe the evolution of the explosion
right from the start,' Berger said. 'This eventually confirmed that the big
X-ray blast marked the birth of a supernova.'
The discovery was a case of serendipity, Soderberg said, as the team had NASA's
Swift satellite pointed at NGC 2770 to observe supernova SN 2007uy (located 90
million light years from Earth in the constellation Lynx) and happened to catch
the X-ray outburst.
'We were in the right place, at the right time, with the right telescope on
January 9th and witnessed history,' Soderberg said.
World-wide monitoring
After observing the X-ray outburst, Soderberg mounted an international observing
campaign, with telescopes all over the world joining in to monitor the baby
supernova, including the Hubble Space Telescope, the Gemini South Telescope in
Chile, Lick Observatory and the Keck I telescope in Hawaii, among others.
The combined observations helped to pin down the energy of the initial X-ray
burst and showed that it was a typical Type Ibc supernova, which occurs when a
massive, compact star explodes.
The observations will also provide insight into the early stages of supernovas.
'This first instance of catching the X-ray signature of stellar death is going
to help us fill in a lot of gaps about the properties of massive stars, the
birth of neutron stars and black holes, and the impact of supernovae on their
environments,' said Neil Gehrels, principal investigator of the Swift satellite.
Studying this initial X-ray outburst will also give astronomers a signature to
help them spy other newborn supernovas and set their time of explosion to within
a few seconds, instead of a few days like previous timing estimates.
'We also now know what X-ray pattern to look for,' Gehrels said. 'Hopefully we
will be able to find many more supernovae at this critical moment.'

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