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Gamma-Ray
Lighthouse At The Edge Of Our Universe
Thursday, October 4, 2007
Artist's
impression of a blazar
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This
is an artist's impression of a blazar. A blazar is a very
compact and highly variable energy source associated with a
supermassive black hole. It is also characterized by a
relativistic jet that is pointing in the general direction of
the Earth. Blazars are among the most violent phenomena in the
universe and are an important topic in extragalactic astronomy.
Credits:
Boston University - Cosmovision
There is a gamma-ray
lighthouse shining from the edge of our universe. Astronomers
have discovered it using ESA’s orbiting gamma-ray
observatory, Integral. Now, they must work hard to understand
it.
The object, known only by its catalog name IGR
J22517+2218, was discovered this year, but its nature was
unknown. This is not an unusual situation. Around 30% of the
sources discovered by Integral remain unidentified so far. All
astronomers know for certain, is that there are celestial sources
out there, pumping gamma rays into space. However, the
identification of the sources with individual celestial objects
will have to wait for more detailed observations in other
wavelengths.
In fact, this was the case for
IGR J22517+2218. It came as a surprise when NASA’s Swift
satellite recorded the object in X-rays, giving its position
within much more precision than can be achieved in gamma-rays.
IGR J22517+2218 was identified with the already known active
galaxy MG3 J225155+2217. This galaxy is so distant that it is the
furthest celestial object ever to be recorded by Integral.
“It
is gobbling up an entire solar system every few days and hurling
the energy out in gamma-rays” All
active galaxies are powered by supermassive black holes. These
celestial monsters contain between a million and several thousand
million times the mass of the Sun.
They generate a gravitational
field so large that they swallow any matter passing nearby,
releasing enormous amounts of energy in the process. In the case
of IGR J22517+2218, the Integral observations show that it is a
gargantuan powerhouse, throwing out stupendous quantities of
gamma rays.
“It is gobbling up an
entire solar system every few days and hurling the energy out in
gamma-rays,” says Loredana Bassani, IASF-Bologna/INAF,
Italy, who together with colleagues has investigated this distant
galaxy.
The Integral observations show
that the galaxy is one of a special kind of active galaxy, known
as a blazar. These are the most energetic of the active galaxies.
However, the Integral data does show some curiosities.
“This is a very peculiar
object. We have been able to classify it as a blazar but it has
some strange characteristics,” says Bassani.
Blazars tend to have two major
peaks of emission. In objects similar to IGR J22517+2218, one
peak occurs in infrared wavelengths and is produced by the
radiation given off by electrons spiraling around the magnetic
field lines. The other peak occurs at high-energy gamma-ray
wavelengths and is produced by those same electrons colliding
with photons of light.
In the case of IGR J22517+2218,
the object appears to have only one peak. This occurs in neither
of the conventional wavelength ranges but, in fact, in the
low-energy gamma-ray band instead. Either the infrared peak has
been moved up in energy, or the high-energy gamma-ray peak has
been moved down.
Either way, when the team can
work out what this means, it will doubtlessly tell them a lot
about active galaxies, and blazars in particular. “Whatever
we discover, this object will stretch our understanding of the
blazars,” says Bassani.
The team hope to continue
observing this object at all wavelengths in an effort to build up
a full picture of the radiation given out by this celestial
object. In this way, they will be able to piece together the
manner in which the supermassive black hole at the heart of IGR
J22517+2218 is devouring its surroundings.
Source: ESA
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