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Ref: RAS PN09/34 (NAM 21)
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CHANDRA SHOWS SHOCKING IMPACT OF GALAXY JET
A
survey by the Chandra X-ray observatory has revealed in detail, for
the first time, the effects of a shock wave blasted through a galaxy
by powerful jets of plasma emanating from a supermassive black hole
at the galactic core. The
observations of Centaurus A, the nearest galaxy that contains these
jets, have enabled astronomers to revise dramatically their picture
of how jets affect the galaxies in which they live. The results will
be presented on Wednesday 22nd
April at the European Week of Astronomy and Space Science in Hatfield
by Dr Judith Croston of the University of Hertfordshire.
A team led by Dr Croston and Dr Ralph Kraft, of the Harvard-Smithsonian Center for Astrophysics in the USA, used very deep X-ray observations from Chandra to get a new view of the jets in Centaurus A. The jets inflate large bubbles filled with energetic particles, driving a shock wave through the stars and gas of the surrounding galaxy. By analysing in detail the X-ray emission produced where the supersonically expanding bubble collides with the surrounding galaxy, the team were able to show for the first time that particles are being accelerated to very high energies at the shock front, causing them to produce intense X-ray and gamma-ray radiation. Very high-energy gamma-ray radiation was recently detected from Centaurus A for the first time by another team of researchers using the High Energy Stereoscopic System (HESS) telescope in Namibia.
"Although we expect that galaxies with these shock waves are common in the Universe, Centaurus A is the only one close enough to study in such detail," said Dr Croston. "By understanding the impact that the jet has on the galaxy, its gas and stars, we can hope to understand how important the shock waves are for the life cycles of other, more distant galaxies."
The powerful jets are found in only a small fraction of galaxies but are most common in the largest galaxies, which are thought to have the biggest black holes. The jets are believed to be produced near to a central supermassive black hole, and travel close to the speed of light for distances of up to hundreds of thousands of light years. Recent progress in understanding how galaxies evolve suggests that these jet-driven bubbles, called radio lobes, may play an important part in the life cycle of the largest galaxies in the Universe.
Energetic
particles from radio galaxies may also reach us directly as cosmic
rays hitting the Earth's atmosphere. Centaurus A is thought to
produce many of the highest energy cosmic rays that arrive at the
Earth. The team believe that their results are important for
understanding how such high-energy particles are produced in galaxies
as well as for understanding how massive galaxies evolve.
The results of this research will be published in a forthcoming issue of the Monthly Notices of the Royal Astronomical Society.
NOTES FOR EDITORS
Chandra X-ray Observatory
NASA's Chandra X-ray Observatory, one of NASA’s four great observatories, was launched by the Space Shuttle Columbia on July 23, 1999. It is designed to observe X-rays from high-energy regions of the universe, such as the remnants of exploded stars. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar.
For
further details, see: http://chandra.harvard.edu/about/index.html
Centaurus
A
Centaurus A (NGC 5128) is the nearest active galaxy to Earth. It is located about 14 million light-years away in the constellation Centaurus. Its structure suggests that it is an example of an elliptical galaxy that has been disrupted by a collision with a smaller spiral galaxy.
IMAGES
An image can be found at:
http://hercules.herts.ac.uk/~jcroston/cena_shock.png
Caption:
The image shows in red the X-ray emission produced by high-energy
particles accelerated at the shock front where Centaurus A's
expanding radio lobe (shown in blue) collides with the surrounding
galaxy. (In the top-left corner X-ray emission from close to the
central black hole, and from the X-ray jet extending in the opposite
direction can also be seen.)
Contacts:
Dr Judith Croston
Research Fellow
Centre
for Astrophysics Research
Science and Technology Research
Institute
University of Hertfordshire
College Lane
Hatfield,
AL10 9AB
United Kingdom
Tel:
01707
284942
E-mail:
J.H.Croston@herts.ac.uk