Nature has again thrown astronomers for a loop. Just when they thought
they understood how gamma-ray bursts formed, they have uncovered what
appears to be evidence for a new kind of cosmic explosion. These seem
to arise when a newly born black hole swallows most of the matter from
its doomed parent star.
Three-colour
image (B, V, and R-band) of the gamma-ray burst observed on 5 May 2006,
GRB 060505, with FORS on the VLT. The galaxy is a spiral galaxy at a
distance of 1300 million light-years. The yellow arrow shows where the
star exploded, namely in a star-forming region in one of the spiral
arms of the galaxy. (Image courtesy of European Southern Observatory)
Gamma-ray bursts (GRBs), the
most powerful explosions in the Universe, signal the formation of a new
black hole and come in two flavours, long and short ones. In recent
years, international efforts have shown that long gamma-ray bursts are
linked with the explosive deaths of massive stars (hypernovae).
Last
year, observations by different teams - including the GRACE and MISTICI
collaborations that use ESO's telescopes - of the afterglows of two
short gamma-ray bursts provided the first conclusive evidence that this
class of objects most likely originates from the collision of compact
objects: neutron stars or black holes.
The newly found
gamma-ray bursts, however, do not fit the picture. They instead seem to
share the properties of both the long and short classes.
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