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 analyzing 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.
