These extremely dense objects can't 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 neighboring gas and stars finally spiral into the black hole, a substantial fraction of the infalling mass is transformed into pure energy.

It is not yet understood how, long before this dramatic event takes place, all that material is moved from the outer regions of the galaxy toward the central region.

To cast more light on this subject, 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 in northern Chile.

The ISAAC instrument is particularly well suited to this type of observation. Visible light can't 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 bars are dynamical structures that "open a road" for the flow of material toward the innermost region.

The research team was surprised to discover signs of a young stellar population near the centers 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 center and suffer an unhappy fate...

Related images:

NGC 1097

NGC 1808

NGC 5728

The Role of Nuclear Bars

[Contact: Eric Emsellem]

15-Aug-2001