In this illustration, the position of a dark,
absorbing cloud of material is located high above the supermassive black hole
and accretion disk in the center of the active galaxy NGC 5548. Numerous other
filaments twist around the black hole as they are swept away by a torrent of
radiation "winds."
Image Credit: NASA, ESA, and A. Feild (STScI)
An international team of astronomers, using data from several NASA and
European Space Agency (ESA) space observatories, has discovered unexpected
behavior from the supermassive black hole at the heart of the galaxy NGC 5548,
located 244.6 million light-years from Earth. This behavior may provide new
insights into how supermassive black holes interact with their host
galaxies.
Immediately after NASA's Hubble Space Telescope observed NGC 5548 in June
2013, this international research team discovered unexpected features in the
data. They detected a stream of gas flowing rapidly outward from the galaxy's
supermassive black hole, blocking 90 percent of its emitted X-rays.
"The data represented dramatic changes since the last observation with Hubble
in 2011," said Gerard Kriss of the Space Telescope Science Institute (STScI) in
Baltimore, Maryland. "I saw signatures of much colder gas than was present
before, indicating that the wind had cooled down due to a significant decrease
in X-ray radiation from the galaxy's nucleus."
The discovery was made during an intensive observing campaign that also
included data from NASA's Swift spacecraft, Nuclear Spectroscopic Telescope
Array (NuSTAR) and Chandra X-ray Observatory, as well as ESA's X-ray
Multi-Mirror Mission (XMM-Newton) and Integral gamma-ray observatory
(INTEGRAL).
After combining and analyzing data from all six sources, the team was able to
put together the pieces of the puzzle. Supermassive black holes in the nuclei of
active galaxies, such as NGC 5548, expel large amounts of matter through
powerful winds of ionized gas. For instance, the persistent wind of NGC 5548
reaches velocities exceeding 621 miles (approximately 1,000 kilometers) a
second. But now a new wind has arisen, much stronger and faster than the
persistent wind.
"These new winds reach speeds of up to 3,107 miles (5,000 kilometers) per
second, but is much closer to the nucleus than the persistent wind," said lead
scientist Jelle Kaastra of the SRON Netherlands Institute for Space Research.
"The new gas outflow blocks 90 percent of the low-energy X-rays that come from
very close to the black hole, and it obscures up to a third of the region that
emits the ultraviolet radiation at a few light-days distance from the black
hole."
The newly discovered gas stream in NGC 5548 -- one of the best-studied of the
type of galaxy know as Type I Seyfert -- provides the first direct evidence of a
shielding process that accelerates the powerful gas streams, or winds, to high
speeds. These winds only occur if their starting point is shielded from
X-rays.
It appears the shielding in NGC 5548 has been going on for at least three
years, but just recently began crossing their line of sight.
"There are other galaxies with similar streams of gas flowing outward from
the direction of its central black hole, but we've never before found evidence
that the stream of gas changed its position as dramatically as this one has,"
said Kriss. "This is the first time we've seen a stream like this move into our
line of sight. We got lucky."
Researchers also deduced that in more luminous quasars, the winds may be
strong enough to blow off gas that otherwise would have become "food" for the
black hole, thereby regulating both the growth of the black hole and that of its
host galaxy.
These results are being published online in the Thursday issue of Science
Express.
The Hubble Space Telescope is a project of international cooperation between
NASA and the European Space Agency. NASA's Goddard Space Flight Center in
Greenbelt, Maryland, manages the telescope. STScI conducts Hubble science
operations and is operated for NASA by the Association of Universities for
Research in Astronomy, Inc., in Washington.
For images and more information about Hubble, visit:
NASA
Guillermo Gonzalo Sánchez Achutegui
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