WHEN supernova 1987A exploded 12 years ago, stellar debris was ejected in a
narrow jet travelling at close to the speed of light. Astronomers who have
reanalysed observations made at the time say this finding strengthens the case
for a connection between the dramatic gamma-ray bursters and exploding
stars.
SN1987A, the brightest supernova recorded in more than 400 years, created a
sensation when it appeared in a neighbouring galaxy, the Large Magellanic Cloud.
Peter Nisenson and Costas Papaliolios of the Harvard-Smithsonian Center for
Astrophysics in Cambridge, Massachusetts, made high-resolution images of the
exploding star 30 and 38 days later.
These images showed a spot with about a tenth of the brightness of the
supernova about 17 millionths of a degree away. At the time, scientists
published papers about this spot, Nisenson says, but they never reached any
consensus on what it was.
Using state-of-the-art image-processing techniques, Nisenson and Papaliolios
have now reanalysed their images and have found another less bright spot on the
other side of the supernova, about 42 millionths of a degree away. “The two
spots and the supernova were aligned, strongly suggesting we were seeing a
two-sided jet emerging from the explosion,” says Nisenson. Their results, which
will appear later this year in Astrophysical Journal Letters, suggest
that matter was ejected by the explosion in a jet moving almost as fast as
light.
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In January, another jet firing off directly towards the Earth
coincided with a powerful gamma-ray burst
(This Week, 3 April, p 5).
The source of such bursts—enormously powerful flashes
of gamma rays from near the edge of the
visible Universe—has been a matter of heated debate. But if supernovae
create jets, as the new results suggest, this would provide compelling evidence
that the sources of gamma-ray bursters and powerful explosions of stars are
one and the same thing.
Bohdan Paczynski, an expert on gamma-ray bursters at Princeton University in
New Jersey, says this link is intriguing: “It’s a giant step in a direction I
like a lot.” But he warns against generalising too much. “We should be aware of
the possibility that not every supernova has a relativistic jet, and not every
relativistic jet must produce a gamma-ray burst.”
More evidence for the link was announced by Brian Schmidt of the Australian
National University in Canberra last week. He says the postion of a gamma-ray
burster in 1997 coincided with an unusually bright supernova.
