Artist's concept of a supermassive black hole at the centre of a galaxy.
Credit: NASA / JPL / Caltec
Astronomers see huge clouds of gas orbiting supermassive black holes at
the centres of galaxies. Once thought to be a relatively uniform,
fog-like ring, the accreting matter instead forms clumps dense enough to
intermittently dim the intense radiation blazing forth as these
enormous objects condense and consume matter.
The international team reports their sightings in a paper to be
published in the Monthly Notices of the Royal Astronomical Society,
available online now. Videos depicting the swirling clouds are posted to
YouTube.
Evidence for the clouds comes from records collected over 16 years by
NASA's Rossi X-ray Timing Explorer, a satellite in low-earth orbit
equipped with instruments that measured variations in X-ray sources.
Those sources include active galactic nuclei, brilliantly luminous
objects powered by supermassive black holes as they gather and condense
huge quantities of dust and gas.
By sifting through records for 55 active galactic nuclei Alex Markowitz, an astrophysicist at the University of California, San Diego and the Karl Remeis Observatory in Bamberg, Germany and colleagues found a dozen instances when the X-ray signal dimmed for periods of time ranging from hours to years, presumably when a cloud of dense gas passed between the source and satellite.
Mirko Krumpe of the European Southern Observatory in Garching,
Germany and Robert Nikutta, of Andrés Bello University in Santiago,
Chile co-authored the report, which confirms what recent models of these
systems have predicted.
The clouds they observed orbit a few light-weeks to a few light-years
from the centre of the active galactic nuclei. One, in a spiral galaxy
in the direction of the constellation Centaurus designated NGC 3783,
appeared to be in the midst of being torn apart by tidal forces.
Support for this research came from NASA's Astrophysics Data Analysis
Program (NNX11AD07G) and the European Community's Seventh Framework
Program (229517). Nikutta acknowledges support from ALMA-CONICYT
(31110001). Video produced by the Scientific Visualization Studio,
Goddard Spaceflight Centre, NASA, based in part on visualisations
created by Wolfgang Steffen, Institute of Astronomy, National Autonomous
University of Mexico.
Science contacts
Alex Markowitz, in Germany
almarkowitz@ucsd.edu (preferred)
Tel: +49 (0)951 95222 26
Available for interviews in English only
Mirko Krumpe, in California, U.S.
Tel: +1 858 822 3435
mkrumpe@eso.org
Available for interviews in German (preferred) or English
Robert Nikutta, in Chile
Tel: +56 9 7370 1865
Available for interviews in German or English
Animations
YouTube animations of clouds in orbit around a black hole are available from
http://www.youtube.com/watch?v=fUQ29PQBXhQ
http://www.youtube.com/watch?v=vdQm9VGj7g4 (with weather symbols)
http://www.youtube.com/watch?v=OCLpFTm01VA (with a diagram showing changing X-ray emission)
A NASA video with accompanying soundtrack is available from http://youtu.be/QA8nzRkjOE
Further information
The researchers publish their work in “First X-ray-based statistical
tests for clumpy-torus models: eclipse events from 230 years of
monitoring of Seyfert AGN”, A. G. Markowitz, M. Krumpe and R. Nikutta4,
Monthly Notices of the Royal Astronomical Society. The paper is
available from http://mnras.oxfordjournals.org/content/early/2014/02/04/mnras.stt2492
Notes for editors
The Royal Astronomical Society (RAS, www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy,
solar-system science, geophysics and closely related branches of
science. The RAS organizes scientific meetings, publishes international
research and review journals, recognizes outstanding achievements by the
award of medals and prizes, maintains an extensive library, supports
education through grants and outreach activities and represents UK
astronomy nationally and internationally. Its more than 3800 members
(Fellows), a third based overseas, include scientific researchers in
universities, observatories and laboratories as well as historians of
astronomy and others.
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