Centaurus A (NGC 5128)
|Dark lanes of dust crisscross the giant elliptical
galaxy Centaurus A. This image, taken with Hubble's Wide Field Camera
3 in July 2010, reveals the glow of young, blue star clusters and
a glimpse into regions normally obscured by the dust. The warped shape
of Centaurus A's disk of gas and dust is evidence for a past collision
and merger with another galaxy. The resulting shock waves cause hydrogen
gas clouds to compress, triggering a firestorm of new star formation.
These are visible in the red patches in this Hubble close-up. Credit:
NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration
Centaurus A (NGC 5128) is the second strongest extragalactic radio
source in the sky (after Cygnus A) and the
nearest radio galaxy and active
galactic nucleus to the Milky Way; it lies in the constellation Centaurus,
just over 11 million light-years away in the M83 group of galaxies. Cen
A's optical counterpart, discovered by James Dunlop in 1826, is an unusual elliptical galaxy (NGC 5128) bisected by a dark circumgalactic dust belt that appears to be
debris from a merger between the elliptical and at least one spiral galaxy
over the past few billion years.
Cen A radio emission
At radio wavelengths, Cen A show two vast lobes of radio emission, that
extend thousands of light-years in opposite directions along the polar axis
of the disk of NGC 5128. The most active radio emission, however, is associated
with Cen A's compact core which is the foremost example of a radio-loud
active galactic nucleus and, at only 10 light-days across, the smallest
known extragalactic radio source. Infrared measurements have revealed high-speed
motions in this core that indicate a fast-spinning disk containing some
200 million solar masses of material. These data confirm a previous suspicion
that the active nucleus of Cen A is powered by a supermassive
black hole with a mass of about 100 million solar masses.
The spiral arms of Cen A
As a result of the collision in which Centaurus A gained its famous wide
dust lane, it also, observations published in 2012 revealed, sprouted a pair of spiral arms – making it unique among all known
elliptical galaxies. However, the spiral arms of Cen A are not made mostly
of stars as in the case of spiral galaxy like the Milky Way but instead
of molecular gas. The arms were discovered from a detailed study of the
dust lane region at the radio wavelengths emitted by carbon monoxide molecules.
Such structures may exist in other elliptical galaxies, too, but would not
be easy spot at great distances.
- Espada, D., et al. "Disentangling the circumnuclear environs of Centaurus
A: gaseous spiral arms in a giant elliptical galaxy". ApJ,
756, L10 (2012) doi:10.1088/2041-8205/756/1/L10