Press Release

Black hole monster in a spin releases energy!

By SpaceRef Editor
October 22, 2001
Filed under , ,

Black holes may be worse monsters than we thought. Not only do they
inexorably devour matter around them, but they may also be able to
steadily belch out energy. This is the conclusion of a European-led team
of astronomers whose work with ESA’s XMM-Newton X-ray observatory has
produced surprising new results.

Black holes can contain the mass of a billion Suns compressed into the
space the size of the Solar System. Their gravitational fields are so
intense that nothing – not even light – can escape their attraction.
Before being swallowed, the gas and dust takes the form of a fast rotating
accretion disc, a disc of material which has accumulated around the black
hole, where friction causes it to glow strongly in X-rays.

The spiral galaxy MCG-6-30-15, situated 100 million light-years away, was
targeted by XMM-Newton in June 2000 for a team of astronomers led by Dr.
Jörn Wilms, from the Astronomy and Astrophysics Institute at the
Eberhard-Karls University in Tuebingen, Germany. The data obtained has led
them to conclude that energy is not only going in to the galaxy’s black
hole, but is also escaping.

“With XMM-Newton’s great collecting power we have discovered something
never observed before in a black hole,” explains Jörn Wilms. “The
observatory’s EPIC cameras have obtained a spectrum, a kind of chemical
fingerprint of the elements present. This graph displays an unusually
broad ‘line’ for the X-ray emission corresponding to the presence of iron
in the accretion disc. This broad line had first been detected in 1995
with the ASCA satellite but we had never seen it so clearly. And, it is
full of surprising features.”

Analysis of this iron line has led the team to deduce that the broad line
arises from X-ray emission stemming from the innermost areas of the
accretion disc, just before matter disappears into the black hole. But the
number of photons and their energies measured by XMM-Newton far exceed
what could be expected from the established models for accretion discs of
supermassive black holes. It was clear to the team that something else was
“powering up” the iron atoms which glow so much in X-rays.

The hunt for a suitable explanation involved intensive spectral modelling
and theoretical mathematics, one of whose parameters included the fact
that the data shows that the black hole itself is rotating.

According to the team, one model fits the XMM-Newton data well. It
corresponds to a theory proposed over 25 years ago by two Cambridge
University astronomers. Roger Blandford and Roman Znajek had suggested
that rotational energy could escape from a black hole when it is in a
strong magnetic field which exerts a braking effect. This theory fits the
physical laws of thermodynamics which state that energy released should be
absorbed by the surrounding gas.

“We have probably seen this electric dynamo effect for the very first
time. Energy is being extracted from the black hole’s spin and is conveyed
into the innermost parts of the accretion disc, making it hotter and
brighter in X-rays,” says Jörn Wilms.

Co-investigator Dr. Christopher Reynolds at the University of Maryland and
other American members of the team contributed greatly to the theoretical
interpretation of the data. “Never before have we seen energy extracted
from black holes. We always see energy going in, not out,” says Reynolds,
who performed much of the analysis whilst at the University of Colorado.
Other scientists involved in this work are James Reeves of Leicester
University, United Kingdom, and Silvano Molendi of the Instituto di Fisica
Cosmica “G. Occhialini”, Milan, Italy.

The team’s conclusion that a magnetodynamic process is involved is already
provoking intense debate. “We recognise that more observations are
required to confirm our work,” says Jörn Wilms. “But there is no disputing
the presence of this exceptionally strong iron line in the spectrum of
MCG-6-30-15. It is extremely puzzling and an explanation must be found.”

One thing is sure: only a couple of years ago, before operations with the
European X-ray observatory began, no one would have dared propose such
interpretations. Sufficiently detailed spectra of the kind today provided
by XMM-Newton were just not available.

REFERENCE

“XMM-EPIC observation of MCG-6-30-15: Direct evidence for the extraction
of energy from a spinning black hole?” by Jörn Wilms, Christopher S.
Reynolds, Mitchell C. Begelman, James Reeves, Silvano Molendi, Rüdiger
Staubert and Eckhard Kendziorra, to be published in the Monthly Notices of
the Royal Astronomical Society.

NOTE TO THE EDITORS

The XMM-Newton observatory, ESA’s second ‘Cornerstone’ mission, was
launched in December 1999. It carries three advanced X-ray telescopes with
an unprecedented X-ray collecting power. Its instruments were provided by
large European consortia, including American institutes. NASA helped fund
the mission development and supports guest observatory time.

For more information please contact:

Dr. Fred Jansen

XMM-Newton Project Scientist, ESA-ESTEC, The Netherlands

Tel: +31.71.565.4426

Email: [email protected]

DR. JÖRN WILMS

Institute for Astronomy and Astrophysics, Eberhard-Karls University,

Tuebingen, Germany

Email: [email protected]

Tel: +49 7071 29-76128

DR. CHRISTOPHER REYNOLDS

University of Maryland, USA

Tel: + 1 301.405.2682

Email: [email protected]

To know more about XMM and ESA’s Science Programme visit:

http://sci.esa.int

SpaceRef staff editor.