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2009-12-03 08:48:52
Clara Moskowitz
Staff Writer
SPACE.com clara Moskowitz
staff Writer
space.com Wed Dec 2, 1:15 pm ET
All supernova explosions are violent affairs, but this one takes the cake.
Astronomers have spotted a new type of extremely bright cosmic explosion they
think originates from an exceptionally massive star.
This breed of explosion has been long predicted, but never before seen. Like
all supernovas, the blast is thought to have marked the end of a star's life.
But in this case, that star may have started out with 200 times the mass of the
sun.
The supernova in question, SN2007bi, was observed in 2007 in a nearby dwarf
galaxy. Scientists knew at once it was something different because it was about
50 to 100 times brighter than a typical supernova.
"It was much brighter, and it was bright for a very long time," said researcher
Paolo Mazzali of the Max-Planck Institute for Astrophysics in Germany. "We
could observe this thing almost two years after it was discovered, where you
normally don't see anything anymore."
After analyzing its signature, astronomers published a paper in the Dec. 3
issue of the journal Nature confirming that it matches theoretical predictions
of a so-called pair-instability supernova.
"There were some doubts that they existed," said astronomer Norbert Langer of
the University of Bonn in Germany, who did not work on the project. Langer
wrote an opinion essay on the finding in the same issue of Nature. "There were
severe doubts that stars that massive could ever form in the universe. Now we
seem to be very sure that there was a star with 200 solar masses."
In a pair-instability supernova, the star has neared the end of its life and
exhausted its main supplies of hydrogen and helium, leaving it a core of mostly
oxygen. In smaller stars, the core continues to burn until eventually it is all
iron, then collapses in a Type II supernova, leaving behind a remnant black
hole or neutron star.
But in the case of an extremely massive star, while its core is still made of
oxygen, it releases photons that are so energetic, they create pairs of
electrons and their anti-matter opposites, positrons. When the matter and
antimatter meet, they annihilate each other. This reaction reduces the star's
pressure, and it collapses, igniting the oxygen core in a runaway nuclear
explosion that eats up the whole star, leaving no remnant at all.
The discovery of this rare type of supernova suggests that a few stars actually
can grow into such large behemoths which has long been a topic of debate.
"I was never a believer in very massive stars," Mazzali told SPACE.com. "Seeing
something like this explode means these things exist. This is a fairly new
development in the formation of stars."