A supernova
spotted earlier this year may actually represent a cosmic event closer to
energetic gamma ray bursts, rather than classic stellar explosions.
European
researchers now suggest that the supernova known as SN 2008D resulted from a
massive star collapsing into a black hole. That event produced a five-minute
long burst of X-rays, which NASA's Swift telescope detected on January 9, 2008.
"Our
observations and modeling show this to be a rather unusual event, to be better
understood in terms of an object lying at the boundary between normal
supernovae and gamma-ray bursts," said Paolo Mazzali, an Italian
astrophysicist at the Padova Observatory and Max-Planck Institute for
Astrophysics.
Stars that
were about eight times more massive at birth than our sun end their relatively
short life in a cataclysmic explosion and collapse into either neutron stars or
black holes. The massive exploding stars emit a short
cry of agony in the form of light, X- or gamma-rays, with gamma-rays being
the most energetic.
Mazzali's
team found that the early behavior of the supernova indicated that it was a
highly energetic event for a supernova, although not quite as powerful as a
gamma-ray burst. Theoretical models show that the original star was at birth as
massive as 30 times the Sun, but had lost so much mass that at the time of the
explosion the star had a mass of only 8 to10 solar masses. The likely result of
the collapse of such a massive star is a black
hole.
The original
star also shed much of its hydrogen and helium-rich outer layers before
exploding, characteristics normally associated with gamma-ray bursts. However,
Mazzali's team saw a helium signature still lingering in the explosion's
aftermath, which suggests that the star did not quite reach the level of a
gamma-ray burst.
This
presents an alternative explanation to one detailed earlier in the journal Nature
by another group of astronomers. That team suggested that X-rays were detected
only because stargazers caught the star in the act of
exploding, and that the event was a more typical supernova.
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