3C442A: Galaxy Collision Causes Role Reversal (Forwarded)

Megan Watzke
Chandra X-ray Center, Cambridge, Mass. March 29, 2007
(Phone: 617/496-7998)

3C442A: Galaxy Collision Causes Role Reversal
[http://chandra.harvard.edu/photo/2007/3c442a/]

Astronomers think that there are enormous black holes at the centers of
most, if not all, galaxies. These black holes, which can be millions or even
billions of times more massive than the Sun, can greatly affect the galaxy
and the environments around them. One way such black holes shape their
surroundings is by generating powerful jets of high-energy particles. The
jets, which are bright in radio waves, have been seen to push around the hot
gas that envelops the galaxy. When this happens, astronomers can detect huge
cavities and powerful shock fronts in the hot, X-ray emitting gas.

However, the opposite scenario is apparently unfolding in the galaxy known
as 3C442A. X-ray data from NASA's Chandra X-ray Observatory and radio
observations from the NSF's Very Large Array show that the hot gas (blue) in
the middle of 3C442A is pushing apart the radio-bright gas (orange). The
inner sections of the radio structure are sharp and concave, which is
consistent with the idea that the X-ray bright gas is sweeping the
radio-emitting gas aside. This is the first convincing evidence for such a
role reversal.

A team of scientists, led by Diana Worrall of University of Bristol, UK, has
studied this system and determined why the dynamics in 3C442A seem to be
topsy-turvy. First, there are two galaxies near the middle of 3C442A which
are in the process of merging. These two galaxies are on their second pass
toward a collision, having already experienced a close encounter. The energy
generated from this impending merger is heating the combined atmospheres
from these two galaxies, causing them to shine brightly in X-rays and
expand.

The researchers determined that the jets that had produced the lobes of
radio-emitting gas are no longer active. The jets may have ceased at the
time of, and possibly as a result of, the galaxy collision. Since the
radio-emitting gas no longer has a power source, it is then at the mercy of
the expanding hot gas and has been pushed aside.