Centaurus A is a well-studied galaxy about 10 million light-years away. Now
it has been seen in even greater detail with the infrared eye of NASA's Spitzer
Space Telescope. This image, released yesterday, shows the remains of merger
and helps explain the galaxy's history.
About 200 million years ago, this galaxy is believed to have consumed a smaller
spiral galaxy, the contents of which appear to be churning inside Centaurus
A's core, triggering new generations of star birth.
Also remaining is a parallelogram-shaped structure of dust that's wrapped tightly
around the very center of the galaxy.
The image was presented at a meeting of the American Astronomical Society in
Denver.
While previous observations with other telescopes have revealed this galactic
remnant, it appeared as one long and irregular bar of dust.
"Now we can actually see the shape of this structure, which helps us explain
how it arose," said Jocelyn Keene, principal investigator for the new research
and an astronomer at NASA's Jet Propulsion Laboratory and the California Institute
of Technology, both in Pasadena, Calif.
Centaurus A is a type of galaxy known as "elliptical." It is one of the brightest
sources of radio waves in the sky, which suggests the presence of a supermassive
black hole at its center.
Resolving this unusual parallelogram structure has helped astronomers put together
a picture of its history. The geometric shape can be explained using a model
that describes a flat spiral galaxy falling into an elliptical galaxy and becoming
twisted and warped in the process. The folds in the warped disc, when viewed
nearly edge-on, take on the appearance of a parallelogram. The model predicts
that the leftover galaxy will ultimately flatten into a plane before being entirely
devoured by Centaurus A.
Such galactic feeding has long thought to be a mechanism by which giant elliptical
galaxies form and grow, and likely provides the fuel that drives the strong
radio activity surrounding Centaurus A's central black hole.
