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Dancing around the Black Hole
August 14, 2001ISAAC Finds "Cool" Young Stellar Systems at the Centres of Active Galaxies
Supermassive Black Holes are present at the centres of many galaxies, some
weighing hundreds of millions times more than the Sun. These extremely
dense objects cannot be observed directly, but violently moving gas clouds
and stars in their strong gravitational fields are responsible for the
emission of energetic radiation from such "active galaxy nuclei" (AGN).
A heavy Black Hole feeds agressively on its surroundings. When the
neighbouring gas and stars finally spiral into the Black Hole, a
substantial fraction of the infalling mass is transformed into pure
energy. However, it is not yet well understood how, long before this
dramatic event takes place, all that material is moved from the outer
regions of the galaxy towards the central region.
So how is the food for the central Black Hole delivered to the table in
the first place? To cast more light on this central question, a team of
French and Swiss astronomers has carried out a series of trailblazing
observations with the VLT Infrared Spectrometer And Array Camera (ISAAC)
on the VLT 8.2-m ANTU telescope at the ESO Paranal Observatory.
The ISAAC instrument is particularly well suited to this type of
observations. Visible light cannot penetrate the thick clouds of dust and
gas in the innermost regions of active galaxies, but by recording the
infrared light from the stars close to the Black Hole, their motions can
be studied. By charting those motions in the central regions of three
active galaxies (NGC 1097, NGC 1808 and NGC 5728), the astronomers were
able to confirm the presence of "nuclear bars" in all three. These are
dynamical structures that "open a road" for the flow of material towards
the innermost region.
Moreover, the team was surprised to discover signs of a young stellar
population near the centres of these galaxies - stars that have apparently
formed quite recently in a central gas disk. Such a system is unstable,
however, and will soon disrupt. At some moment, many of those young stars
may get too close to the monster in the centre and suffer an unhappy
fate...
The full text of this Press Release (ESO PR 18/01), with 6 photos and
all weblinks, is available at:
http://www.eso.org/outreach/press-rel/pr-2001/pr-18-01.html
European Southern Observatory (ESO)
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