http://news.yahoo.com/s/afp/20090219/sc_afp/sciencespaceastronomy;_ylt=Asi18ANbRoh1kO2TFDJ28WzZn414
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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 hours away.
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 said.
Gamma-ray bursts are the universe's most luminous explosions,
which astronomers believe occur when massive stars run out of
nuclear fuel and collapse.
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 said.
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 energy emissions.
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," Michelson said.
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.