CENTAURUS A - NGC 5128
What Do These Images Tell Us?
Cen A gets its name from radio astronomy. It is one of the first
radio sources to be identified with a galaxy- NGC 5128. As the
nearest active radio galaxy, it has been well studied by
astronomers and is considered a prototype of a major class of
"low-luminosity" active galaxies.
The Chandra X-ray image of Cen A shows a bright source in the nucleus of
the galaxy, which is probably due to a supermassive black hole. The bright
jet extending out from the nucleus to the upper left is due to explosive
or highly energetic activity around the black hole which ejects matter at
high speeds from the vicinity of the black hole. A faint "counter jet" extending
to the lower right can also be seen. This jet is probably pointing away
from us. Numerous point-like sources of X rays are also apparent. These
are probably due to neutron stars or black holes that are accreting matter
from nearby companion stars.
Angular size of the box = 15 arc min, corresponding
to 50,000 light years
Optical images show that NGC5128 is an elliptical galaxy with huge dust
lanes across the middle of the galaxy. This has led astronomers to speculate
that Cen A was the site of a merger between a small spiral galaxy and a
large elliptical galaxy several hundred million years ago. The optical radiation
is primarily from stars.
Angular size of box = 7.5 arc min, corresponding
to 25,000 light years
The infrared image gives a better view of the dust lanes, as well as the
brilliance of the central source. The infrared radiation is produced by
cool stars with temperatures of "only" a few thousand degrees Celsius, and
by dust that has been heated to a few hundred to a thousand degrees.
Angular size of box = 10 arc min, corresponding
to 38,000 light years
The radio image shows striking jet-like structures that flare out from the
center of the galaxy. These structures have been traced well beyond the
galaxy out to distances of 600,000 years. The total length of the radio
jet shown here is about ten arc minutes, or about 30,000 light years in
length. The radio emission is produced by the synchrotron process, in which
high-energy electrons radiate as they spiral around the magnetic field of
Angular size of box = 12.5 arc min corresponding
to 42,000 light years
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