Andrew Yee
December 20th 05, 06:56 PM
University of Hertfordshire
College Lane, Hatfield
Herts AL10 9AB, U.K.
For further information, please contact:
Helene Murphy, University of Hertfordshire
+44 (0)1707 28 4095
Embargo until 14 Dec 2005 18:00 GMT
Breakthrough in puzzle of giant explosions in space
Astronomers at the University of Hertfordshire have helped to solve one of
the longest standing puzzles in astrophysics -- the nature of the enormous
explosions known as short-duration gamma ray bursts (GRBs).
In a paper to be published in Nature this week (15th December), they will
reveal that around 15% of short-duration bursts originate from galaxies
within 300 million light years of the Milky Way -- more than 10 times
closer than previously thought.
Dr Nial Tanvir who is leading the Hertfordshire team commented: "GRBs are
difficult to observe because they last such a short time, and the
signature flash of gamma rays can only be observed by specially-designed
satellites."
He claims that this was one of the reasons that the nature of GRBs
remained completely enigmatic until 1997, when it was found that at least
one variety-- the so-called 'long-duration' bursts, which last for more
than two seconds -- arise in very remote galaxies, billions of light years
distant, and therefore must be the most violent explosions known.
However, the second variety of GRBs -- the short-duration bursts (those
lasting less than two seconds) -- remained mysterious until earlier this
year when a few short bursts were pin-pointed sufficiently well to track
down their host galaxies. From looking at the kinds of galaxies the bursts
were found in, and the way their light faded away, astronomers have
concluded that these events were most likely the result of the merging of
two super-dense objects, called neutron stars.
"Neutron stars are amongst the most bizarre objects known to science and
are incredibly dense," said Dr Robert Priddey, another member of the team.
"A tea-spoon full of neutron star material would weigh tens of billions of
tons. Their intense gravitational fields provide huge reservoirs of energy
which we believe can power GRBs when two neutron stars merge together to
form a black hole."
The Hertfordshire team's new result adds a further, unexpected twist to
the tale: a significant proportion of short bursts seem to originate from
galaxies much more local to us than those previously observed. These
nearby short bursts, could, like their more distant brethren, result from
the catastrophic collision of neutron stars, though if so then their
outbursts must be much weaker. Alternatively they could be a fundamentally
different kind of explosion. A prime candidate could be an exotic object
called a magnetar -- a lone neutron star with a magnetic field a hundred
thousand billion times that of the Earth -- tearing itself apart due to
enormous magnetic stresses.
"An example of such an explosion was seen a year ago coming from a
magnetar in our own Galaxy, the Milky Way, so it seems reasonable to
expect they should occur occasionally in other galaxies too," said Bob
Chapman, a graduate student working on the project as part of his PhD
research: "If so, they would look very much like short-duration GRBs."
"Although we still don't know for sure what produces the short-duration
gamma-ray bursts, this is a crucial breakthrough because in astronomy
knowing where something occurs is often the decisive step towards
understanding it," said Dr Andrew Levan, another Hertfordshire astronomer
involved in the discovery.
Notes for editor:
This work made use of a catalogue of GRBs observed by NASAšs Compton
Gamma-Ray Observatory in the 1990s. This satellite observed over 400
short-duration bursts, but only provided very rough positions for them,
meaning that until now it was completely unclear how far away they were.
The new analysis demonstrates statistically that around 15% of these
bursts are associated with galaxies within about 300 million light years.
Although this is a huge volume of space, it is only a tiny fraction of the
volume over which we see the more powerful long-duration GRBs.
College Lane, Hatfield
Herts AL10 9AB, U.K.
For further information, please contact:
Helene Murphy, University of Hertfordshire
+44 (0)1707 28 4095
Embargo until 14 Dec 2005 18:00 GMT
Breakthrough in puzzle of giant explosions in space
Astronomers at the University of Hertfordshire have helped to solve one of
the longest standing puzzles in astrophysics -- the nature of the enormous
explosions known as short-duration gamma ray bursts (GRBs).
In a paper to be published in Nature this week (15th December), they will
reveal that around 15% of short-duration bursts originate from galaxies
within 300 million light years of the Milky Way -- more than 10 times
closer than previously thought.
Dr Nial Tanvir who is leading the Hertfordshire team commented: "GRBs are
difficult to observe because they last such a short time, and the
signature flash of gamma rays can only be observed by specially-designed
satellites."
He claims that this was one of the reasons that the nature of GRBs
remained completely enigmatic until 1997, when it was found that at least
one variety-- the so-called 'long-duration' bursts, which last for more
than two seconds -- arise in very remote galaxies, billions of light years
distant, and therefore must be the most violent explosions known.
However, the second variety of GRBs -- the short-duration bursts (those
lasting less than two seconds) -- remained mysterious until earlier this
year when a few short bursts were pin-pointed sufficiently well to track
down their host galaxies. From looking at the kinds of galaxies the bursts
were found in, and the way their light faded away, astronomers have
concluded that these events were most likely the result of the merging of
two super-dense objects, called neutron stars.
"Neutron stars are amongst the most bizarre objects known to science and
are incredibly dense," said Dr Robert Priddey, another member of the team.
"A tea-spoon full of neutron star material would weigh tens of billions of
tons. Their intense gravitational fields provide huge reservoirs of energy
which we believe can power GRBs when two neutron stars merge together to
form a black hole."
The Hertfordshire team's new result adds a further, unexpected twist to
the tale: a significant proportion of short bursts seem to originate from
galaxies much more local to us than those previously observed. These
nearby short bursts, could, like their more distant brethren, result from
the catastrophic collision of neutron stars, though if so then their
outbursts must be much weaker. Alternatively they could be a fundamentally
different kind of explosion. A prime candidate could be an exotic object
called a magnetar -- a lone neutron star with a magnetic field a hundred
thousand billion times that of the Earth -- tearing itself apart due to
enormous magnetic stresses.
"An example of such an explosion was seen a year ago coming from a
magnetar in our own Galaxy, the Milky Way, so it seems reasonable to
expect they should occur occasionally in other galaxies too," said Bob
Chapman, a graduate student working on the project as part of his PhD
research: "If so, they would look very much like short-duration GRBs."
"Although we still don't know for sure what produces the short-duration
gamma-ray bursts, this is a crucial breakthrough because in astronomy
knowing where something occurs is often the decisive step towards
understanding it," said Dr Andrew Levan, another Hertfordshire astronomer
involved in the discovery.
Notes for editor:
This work made use of a catalogue of GRBs observed by NASAšs Compton
Gamma-Ray Observatory in the 1990s. This satellite observed over 400
short-duration bursts, but only provided very rough positions for them,
meaning that until now it was completely unclear how far away they were.
The new analysis demonstrates statistically that around 15% of these
bursts are associated with galaxies within about 300 million light years.
Although this is a huge volume of space, it is only a tiny fraction of the
volume over which we see the more powerful long-duration GRBs.