SOFIA finds cool dust around energetic active black holes

Artist illustration of the thick ring of dust that can
obscure the energetic processes that occur near the
supermassive black hole of an active galactic nuclei. The SOFIA
studies suggest that the dust distribution is about 30 percent
smaller than previously thought. Credit: NASA/SOFIA/Lynette
Cook

Researchers at the University of Texas San Antonio using
observations from NASA’s Stratospheric Observatory for
Infrared Astronomy, SOFIA, found that the dust surrounding
active, ravenous black holes is much more compact than
previously thought.

Most, if not all, large galaxies contain a supermassive black
hole at their centers. Many of these black holes are relatively
quiet and inactive, like the one at the center of our Milky Way
galaxy. However, some supermassive black holes are currently
consuming significant amounts of material that are being drawn
into them, resulting in the of huge amounts of energy. These active
black holes are called .

Previous studies have suggested that all active galactic nuclei
have essentially the same structure. Models indicate that
active galactic nuclei have a donut-shaped dust structure,
known as a torus, surrounding the . Using the
instrument called the Faint Object infraRed CAmera for the
SOFIA Telescope, FORCAST, the team observed the infrared
emissions around 11 supermassive in active galactic nuclei located at
distances of 100 million light years and more, and determined
the size, opacity, and distribution of dust in each torus.

In a paper published in the Monthly Notices of the Royal
Astronomical Society
, the team reports that the tori are 30
percent smaller than predicted and that the peak infrared
emission is at even longer infrared wavelengths than previously
estimated. The implication is that the dust obscuring the
central black hole is more compact that previously thought.

They also indicate that active galactic nuclei radiate most of
their energy at wavelengths that are not observable from the
ground because the energy is absorbed by water vapor in Earth’s
atmosphere. SOFIA flies above 99 percent of the Earth’s water
vapor, enabling the research group to characterize the
properties of the torus-shaped dust structures at far-infrared
wavelengths.

“Using SOFIA, we were able to obtain the most spatially
detailed observations possible at these wavelengths, allowing
us to make new discoveries on the characterization of active
galactic nuclei dust tori,” said Lindsay Fuller, graduate
student at the University of Texas San Antonio and lead author
of the published paper.

Future observations are necessary to determine whether or not
all of the observed emission originates with the tori, or if
there is some other component adding to the total emission of
the active galactic nuclei. Enrique Lopez-Rodriguez, principal
investigator of this project and Universities Space Research
Association staff scientist at the SOFIA Science Center said,
“Next, our goal will be to use SOFIA to observe a larger sample
of active galactic nuclei, and at longer wavelengths. That will
allow us to put tighter constraints on the physical structure
of the dusty environment surrounding the active galactic
.”

Explore further:

Obscured supermassive black holes in galaxies

More information: L. Fuller et al. Investigating the
dusty torus of Seyfert galaxies using SOFIA/FORCAST photometry,
Monthly Notices of the Royal Astronomical Society
(2016). DOI:
10.1093/mnras/stw1780

Journal reference:
Monthly Notices of the Royal Astronomical Society

Provided by: NASA

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