A pair of papers that appear in this week’s edition of Nature report on
some interesting astrophysical observations. Two teams from different
continents have found supernovae that have an anomalous
feature: matter is moving away from them at significant fractions of the
speed of light—0.60c and 0.86c. The well known explosion dynamics of a supernova shouldn’t produce that sort of acceleration; in a typical supernova event, matter shouldn’t reach velocities much
beyond three percent the speed of light.
Speeds this great are often associated with gamma ray bursts, but these observations were missing that key component.
“In every respect, these objects look like gamma-ray bursts—except
that they produced no gamma rays,” said Alicia Soderberg, lead author
of one of the papers. Her team examined SN
2009bb, a supernova in the spiral galaxy NGC 3278, nearly 130 million
light years from Earth. The other team examined SN 2007gr, a supernova in spiral galaxy NGC
1058, a scant 35 million light years from Earth.
Using NASA records of known gamma ray bursts, the teams
attempted to find an event that had a spatial and temporal correlation with the supernovae, but none was
identified. Typical gamma ray bursts are thought to be the result of
the acceleration of matter by a black hole, with the matter reaching nearly 99 percent the speed of light. The fast-moving matter here suggests that these supernovae are powered in part by a nascent black
hole at the center left behind after the core collapse.
Casting a wider net for nearby supernovae suggest that these
‘central engine’ driven type Ib/c supernovae are fairly rare, only
accounting for about one percent of all cases. However, the work
provides a new tool for astronomers to be able to detect them in the future. “These observations are the first to show some
supernovae are powered
by a central engine,” Soderberg said. “These new radio techniques now
give us a way to find explosions that resemble gamma-ray bursts without
relying on detections from gamma-ray satellites.”
Nature,
2010. DOI: 10.1038/nature08714
Nature,
2010. DOI: 10.1038/nature08713
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