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> Huge gamma-ray blast spotted 12.2 bln light-years from earth
Huge gamma-ray blast spotted 12.2 bln light-years from earth
Thu Feb 19, 3:58 pm ET AFP/NASA
WASHINGTON (AFP) The US space agency's Fermi telescope has
detected a massive explosion in space which scientists say is the
biggest gamma-ray burst ever detected, a report published Thursday in
Science Express said.
The spectacular blast, which occurred in September in the Carina
constellation, produced energies ranging from 3,000 to more than five
billion times that of visible light, astrophysicists said.
"Visible light has an energy range of between two and three electron
volts and these were in the millions to billions of electron volts,"
astrophysicist Frank Reddy of US space agency NASA told AFP.
"If you think about it in terms of energy, X-rays are more energetic
because they penetrate matter. These things don't stop for anything --
they just bore through and that's why we can see them from enormous
distances," Reddy said.
A team led by Jochen Greiner of Germany's Max Planck Institute for
Extraterrestrial Physics determined that the huge gamma-ray burst
occurred 12.2 billion light years away.
The sun is eight light minutes from Earth, and Pluto is 12 light
Taking into account the huge distance from earth of the burst,
scientists worked out that the blast was stronger than 9,000
supernovae -- powerful explosions that occur at the end of a star's
lifetime -- and that the gas jets emitting the initial gamma rays
moved at nearly the speed of light.
"This burst's tremendous power and speed make it the most extreme
recorded to date," a statement issued by the US Department of Energy
Gamma-ray bursts are the universe's most luminous explosions, which
astronomers believe occur when massive stars run out of nuclear fuel
Long bursts, which last more than two seconds, occur in massive stars
that are undergoing collapse, while short bursts lasting less than
two seconds occur in smaller stars.
In short gamma-ray bursts, stars simply explode and form supernovae,
but in long bursts, the enormous bulk of the star leads its core to
collapse and form a blackhole, into which the rest of the star falls.
As the star's core collapses into the black hole, jets of material
blast outward, boring through the collapsing star and continuing into
space where they interact with gas previously shed by the star,
generating bright afterglows that fade with time.
"It's thought that something involved in spinning up and collapsing
into that blackhole in the center is what drives these jets. No one
really has figured that out. The jets rip through the star and the
supernova follows after the jets," Reddy said.
Studying gamma-ray bursts allows scientists to "sample an individual
star at a distance where we can't even see galaxies clearly," Reddy
Observing the massive explosions could also lift the veil on more of
space's enigmas, including those raised by the burst spotted by
Fermi, such as a "curious time delay" between its highest and lowest
Such a time lag has been seen in only one earlier burst, and "may
mean that the highest-energy emissions are coming from different
parts of the jet or created through a different mechanism," said
Stanford University physicist Peter Michelson, the chief investigator
on Fermi's large area telescope.
"Burst emissions at these energies are still poorly understood, and
Fermi is giving us the tools to understand them. In a few years,
we'll have a fairly good sample of bursts and may have some answers,"
The Fermi telescope and NASA's Swift satellite detect "in the order
of 1,000 gamma-ray bursts a year, or a burst every 100,000 years in a
given galaxy," said Reddy.
Astrophysicists estimate there are hundreds of billions of galaxies.
The Fermi gamma-ray space telescope was developed by NASA in
collaboration with the US Department of Energy and partners including
academic institutions in France, Germany, Italy, Japan, Sweden and
the United States.