The galaxy NGC 1068 is shown above with an active supermassive black
hole at its nucleus. Astronomers studying similar extreme galaxies in
the infrared have found that in man
y cases
material obscuring the nucleus may be located over an extended region, and not confined in a small torus.
At the core of most galaxies including our own Milky Way is a massive
black hole. Material falling into the environment of the black hole
heats up, and can radiate dramatically, sometimes also powering the
ejection of bipolar jets of rapidly moving charged particles. These
so-called active galactic nuclei (AGN) are observed to have roughly two
types of characteristics: bright, rapidly moving hot gas with dust
emission features, or dust absorption with modest (or no) fast gas.
According to the "unified" model of AGN, these and most other
variations in appearance are primarily due to the angle at which a
galaxy and its central engine are seen. In the first case the galaxy is
seen face-on, and fast-moving gas close to the black hole is clearly
visible. In the latter, the whole galaxy as well as a torus of obscuring
dust around the black hole are seen edge-on; the torus blocks our view
of the fast-moving gas and absorbs infrared in characteristic dust
features.
But is this simple model correct in all cases? CfA
astronomers Andy Goulding, Bill Forman, Christine Jones, and Markos
Trichas have undertaken a study of the origin of this infrared dust
absorption feature. They specifically study the nature of the presumed
torus: is it a small, uniform ring of dense material, a large extended
structure of more diffuse material, or is it perhaps composed of many
small dense clumps?
The observed strength the infrared dust
absorption is key to sorting out these differences. The astronomers used
the infrared spectrometer on the Spitzer Space Telescope to examine the
dust feature in all twenty nearby AGN having extremely large columns of
neutral gas .
At the core of most galaxies including our own Milky Way is a massive black hole. Material falling into the environment of the black hole heats up, and can radiate dramatically, sometimes also powering the ejection of bipolar jets of rapidly moving charged particles. These so-called active galactic nuclei (AGN) are observed to have roughly two types of characteristics: bright, rapidly moving hot gas with dust emission features, or dust absorption with modest (or no) fast gas.
According to the "unified" model of AGN, these and most other variations in appearance are primarily due to the angle at which a galaxy and its central engine are seen. In the first case the galaxy is seen face-on, and fast-moving gas close to the black hole is clearly visible. In the latter, the whole galaxy as well as a torus of obscuring dust around the black hole are seen edge-on; the torus blocks our view of the fast-moving gas and absorbs infrared in characteristic dust features.
But is this simple model correct in all cases? CfA astronomers Andy Goulding, Bill Forman, Christine Jones, and Markos Trichas have undertaken a study of the origin of this infrared dust absorption feature. They specifically study the nature of the presumed torus: is it a small, uniform ring of dense material, a large extended structure of more diffuse material, or is it perhaps composed of many small dense clumps?
The observed strength the infrared dust absorption is key to sorting out these differences. The astronomers used the infrared spectrometer on the Spitzer Space Telescope to examine the dust feature in all twenty nearby AGN having extremely large columns of neutral gas .
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