Artist impression of the heart of galaxy NGC 1068, which harbors an actively feeding supermassive black hole. Arising from the black hole's outer accretion disk, ALMA discovered clouds of cold molecular gas and dust. This material is being accelerated by magnetic fields in the disk, reaching speeds of about 400 to 800 kilometers per second. This material gets expelled from the disk and goes on to hide the region around the black hole from optical telescopes on Earth. Essentially, the black hole is cloaking itself behind a veil of its own exhaust. Credit: NRAO/AUI/NSF; D. Berry / Skyworks
ALMA image of the central region of galaxy NGC 1068. The torus of material harboring the supermassive black hole is highlighted in the pullout box. This region, which is approximately 40 light-years across, is the result of material flung out of the black hole's accretion disk.
The colors in this image represent the motion of the gas: blue is material moving toward us, red moving away. The areas in green are low velocity and consistent with rotation around a black hole. The white in the central region means the gas is moving both toward and away at very high speed, the conditions illustrated in the artist impression.
The outer ring area is unrelated to the black hole and is more tied to the structure of the central 1,000 light-years of the host galaxy. Credit: Gallimore et al.; ALMA (ESO/NAOJ/NRAO); B. Saxton (NRAO/AUI/NSF)
Supermassive black holes, millions to billions of times the mass of our
Sun, are found at the centers of galaxies. Many of these galactic
behemoths are hidden within a thick doughnut-shape ring of dust and gas
known as a torus. Previous observations suggest these cloaking,
tire-like structures are formed from the native material found near the
center of a galaxy.
New data from the Atacama Large Millimeter/submillimeter Array (ALMA),
however, reveal that the black hole at the center of a galaxy named NGC
1068 is actually the source of its own dusty torus of dust and gas,
forged from material flung out of the black hole’s accretion disk.
This
newly discovered cosmic fountain of cold gas and dust could reshape our
understanding of how black holes impact their host galaxy and
potentially the intergalactic medium.
"Think of a black hole as
an engine. It's fueled by material falling in on it from a flattened
disk of dust and gas,” said Jack Gallimore, an astronomer at Bucknell
University in Lewisburg, Pennsylvania, and lead author on a paper
published in Astrophysical Journal Letters. "But like any
engine, a black hole can also emit exhaust." That exhaust, astronomers
discovered, is the likely source of the torus of material that
effectively obscures the region around the galaxy's supermassive black
hole from optical telescopes.
NGC 1068 (also known as Messier 77)
is a barred spiral galaxy approximately 47 million light-years from
Earth in the direction of the constellation Cetus. At its center is an
active galactic nucleus, a supermassive black hole that is being fed by a
thin, rotating disk of gas and dust known as an accretion disk. As
material in the disk spirals toward the central black hole, it becomes
superheated and blazes bright with ultraviolet radiation. The outer
reaches of the disk, however, are considerably cooler and glow more
appreciably in infrared light and the millimeter-wavelength light that
ALMA can detect.
Using ALMA, an international team of
astronomers peered deep into this region and discovered a sprinkling of
cool clouds of carbon monoxide lifting off the outer portion of the
accretion disk. The energy from the hot inner disk partially ionizes
these clouds, enabling them to adhere to powerful magnetic field lines
that wrap around the disk.
Like water being flung out of a
rapidly rotating garden sprinkler, the clouds rising above the accretion
disk get accelerated centrifugally along the magnetic field lines to
very high speeds -- approximately 400 to 800 kilometers per second
(nearly 2 million miles per hour). This is up to nearly three times
faster than the rotational speed of the outer accretion disk, fast
enough to send the clouds hurtling further out into the galaxy.
"These
clouds are traveling so fast that they reach 'escape velocity' and are
jettisoned in a cone-like spray from both sides of the disk," said
Gallimore. "With ALMA, we can for the first time see that it is the gas
that is thrown out that hides the black hole, not the gas falling in."
This suggests that the general theory of an active black hole is
oversimplified, he concludes.
With future ALMA observations, the
astronomers hope to work out a fuel budget for this black hole engine:
how much mass per year goes into the black hole and how much is ejected
as exhaust.
"These are fundamental quantities for understanding
black holes that we really don't have a good handle on at this time,"
concludes Gallimore.
The National Radio Astronomy Observatory is a
facility of the National Science Foundation, operated under cooperative
agreement by Associated Universities,
Reference:
This research is presented in the paper titled
“High-velocity bipolar molecular emission from an AGN torus,” by J.
Gallimore et al., published in Astrophysical Journal Letters on 15
September 2016.
Contact:
Charles Blue
NRAO Public Information Officer
+1 434.296.0314; cblue@nrao.edu
The team is composed of Jack Gallimore (Bucknell University,
Lewisburg, Pennsylvania), Moshe Elitzur (University of California,
Berkeley), Roberto Maiolino (University of Cambridge, U.K.), Alessandro
Marconi (University of Firenze, Italy), Christopher P. O’Dea (University
of Manitoba, Winnipeg, Canada), Dieter Lutz (Max Planck Institute for
Extraterrestrial Physics, Garching, Germany), Stefi A. Baum, University
of Manitoba, Winnipeg, Canada), Robert Nikutta (Catholic University of
Chile, Santiago), C.M.V. Impellizzeri (Joint ALMA Observatory, Santiago,
Chile), Richard Davies (Max Planck Institute for Extraterrestrial
Physics, Garching, Germany), Amy E. Kimball (National Radio Astronomy
Observatory, Socorro, New Mexico), Eleonora Sani (European Southern
Observatory, Santiago, Chile).
The Atacama Large Millimeter/submillimeter Array (ALMA), an
international astronomy facility, is a partnership of the European
Organisation for Astronomical Research in the Southern Hemisphere (ESO),
the U.S. National Science Foundation (NSF) and the National Institutes
of Natural Sciences (NINS) of Japan in cooperation with the Republic of
Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in
cooperation with the National Research Council of Canada (NRC) and the
National Science Council of Taiwan (NSC) and by NINS in cooperation with
the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space
Science Institute (KASI).
ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
