Satellite
observations have confirmed how a certain type of star explosion occurs and
revealed a previously unknown stage of radiation release during the stellar
burst.
Using
NASA's Swift
satellite, astronomers observed two dozen supernovas [image]
shortly after they happened. Two, especially, were of special interest.
One, called
SN2005ke [image],
was a Type
1a supernova. These explosions are thought to occur when small, dead stars
called white dwarfs siphon
gas from the atmosphere of either another white
dwarf or a red
giant star. The white dwarfs accumulate matter until they reach a critical
mass of 1.4 solar masses and explode.
Astronomers
use Type 1a supernovas as "standard
candles" to measure cosmic distances because all Type 1a's are thought
to blaze with equal brightness at their peaks, although this has been
challenged by recent observations.
X-ray and
ultraviolet observations by Swift showed shock waves from SN2005ke ramming into
very dense gas that could have only come from a red giant star, confirming at
least one of the Type 1a formation scenarios.
"The
only explanation that we have for X-ray and ultraviolet emission is that this
Type 1a supernova has to have a companion
star. This companion has to be a massive star that is losing a lot of mass
from its stellar wind particles," study leader Stefan Immler of NASA
Goddard Space Flight Center in Maryland told reporters at a press conference.
Also of
interest was SN2006bp [image],
a Type
II supernova created when a massive star ran out of fuel and collapsed under
its own gravity. Swift detected X-ray radiation immediately after the explosion
that had never been seen before and which faded within days. The researchers
were also surprised to find evidence of hot gas lingering near the exploded
star's remains. This suggests that the star's radiation did not create a cavity
around the star before the explosion, as is commonly thought.
"That
was our surprise finding," Immler explained. "We had expected that
the stellar wind blows a cavity
around the star and that there is nothing there that can be shock-heated to
high enough temperatures to give off X-rays."
One
possible explanation for the anomalous gas, Immler said, is that the exploded star might have been a red
supergiant whose stellar wind was slow and dense.
"That's
just the nature of the stellar
wind, if it's a slow enough, dense enough stellar wind, it will not blow a
hole in the environment," he said.
The
research was presented last week at the annual meeting of the High Energy
Astrophysics Division of the American Astronomical Society in San Francisco.
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