New images show the "last meal" of a giant cannibal galaxy
as it gobbles down a smaller spiral galaxy, which has been twisted and warped
from being devoured.
The giant galaxy, Centaurus A (NGC 5128) is the nearest
giant, elliptical galaxy, at a distance of about 11 million light-years. The
galaxy hosts a supermassive black hole that is 200 million times the mass of
the sun, or 50 times the mass of the black hole at the center
of the Milky Way.
At the galaxy's center is an opaque dust lane that is
thought to be the remains of a cosmic
merger between the galaxy and a smaller spiral galaxy full of dust.
Between 200 and 700 million years ago, this galaxy is
believed to have consumed a smaller spiral, gas-rich galaxy — the contents of
which appear to be churning inside Centaurus A's core, likely triggering new
generations of stars.
First glimpses of the "leftovers" of this meal were obtained
thanks to observations with the European Space Agency's Infrared Space
Observatory, which revealed a 16,500 light-year-wide structure, very similar to
that of a small barred galaxy.
More recently, NASA's Spitzer Space Telescope resolved this
structure into
a parallelogram, which can be explained as the remnant of a gas-rich spiral
galaxy falling into an elliptical galaxy and becoming twisted and warped in the
process. Galaxy merging is the most common mechanism to explain the formation
of such giant elliptical galaxies.
The new images, taken by the European Southern Observatory's
3.58-metre New Technology Telescope (NTT) in La Silla, Chile, allow astronomers to get an even sharper view of the structure of this galaxy, completely
free of obscuring dust.
What the astronomers found in the images was surprising:
"There is a clear ring of stars and clusters hidden behind the dust lanes, and
our images provide an unprecedentedly detailed view toward it," said Jouni
Kainulainen, lead author of the paper reporting these results. "Further analysis
of this structure will provide important clues on how the merging process
occurred and what has been the role of star formation during it."
The technique used to observe Centaurus A could help
scientists better understand star formation in galaxies.
"These are the first steps in the development of a new
technique that has the potential to trace giant clouds of gas in other galaxies
at high resolution and in a cost-effective way," said co-author João Alves.
"Knowing how these giant clouds form and evolve is to understand how stars form
in galaxies."
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