Supermassive Black Holes Discovered Devouring Whole Galaxies

100416095800-large Black holes -Stephen Hawking's enigmatic "bad boys of the Universe"-
have been discovered to have the ability to strip massive galaxies of
the cool gases required to form new stars, leaving ageing red giants to
fade out of existence with no stars to replace them.

The
study, led by Asa Bluck of the University of Nottingham's School of
Physics and Astronomy and a Fellow of the Royal Society, used images of
unprecedented depth and resolution from the Hubble Space Telescope and
the Chandra X-Ray Observatory to detect black holes in distant
galaxies. Researchers looked for galaxies emitting high levels of
radiation and x-rays — a classic signature of black holes devouring gas
and dust through accretion, or attracting matter gravitationally., used
images of unprecedented depth and resolution from the Hubble Space
Telescope and the Chandra X-Ray Observatory to detect black holes in
distant galaxies. Researchers looked for galaxies emitting high levels
of radiation and x-rays — a classic signature of black holes devouring
gas and dust through accretion, or attracting matter gravitationally.

Funded
by the Science and Technology Facilities Council and NASA, the research
led to some startling results: in supermassive black holes this
radiation can reach huge proportions, emitting X-ray radiation in far
greater quantities then is emitted by the rest of the objects in the
galaxy combined — meaning that the black hole ‘shines’ far brighter
than the entire galaxy it lies at the heart of. In fact, the amount of
energy released is sufficient to strip the galaxy of gas at least 25
times over.

Results have also shown that the vast majority
of the X-ray radiation present in the universe is produced in these
accretion discs surrounding supermassive black holes, with a small
proportion produced by all other objects, including galaxies and
neutron stars.

The accretions discs surrounding supermassive
black holes produce so much energy that they heat up the cold gases
lying at the heart of massive galaxies. The accretion disc shines
across all wavelengths — from radio waves to gamma waves. This speeds
up the random motions of the gas, making it rise in temperature and
pushing it away from the galactic center, where it becomes less dense.
Gas needs to be cold and dense to collapse under gravity to form new
stars, this resulting hot, low-density material must cool down before
gravity will take effect — a process which would take longer than the
age of the universe to achieve. 

Old stars are therefore left to
die out with no new stars replacing them, leaving the galaxy to grow
dark and die. And by pushing gas away from the galactic centre, the
accretion disc starves the supermassive black hole of new material to
devour, leading to its eventual demise. 

“It’s thought that black
holes form inside their host galaxies and grow in proportion to them,
forming an accretion disc which will eventually destroy the host. In
this sense they can be described as viral in nature,” said Asa Bluck.
“Massive galaxies are in the minority in our visible universe — about
one in a thousand galaxies is thought to be massive, but it may be much
less. And at least a third of these have supermassive black holes at
their centre. That’s why it’s so interesting that this type of black
hole produces most of the X-ray light in the universe. They are the
minority but they dominate energy output.”

Jason McManus via University of Nottingham

http://research.nottingham.ac.uk/NewsReviews/newsDisplay.aspx?id=664

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