Press Release

Cambridge Scientists Follow Doomed Matter on a Ride Around a Black Hole

By SpaceRef Editor
September 9, 2004
Filed under , , ,
Cambridge Scientists Follow Doomed Matter on a Ride Around a Black Hole
2_agn_animation.jpg

Scientists have pieced together the
journey of a bundle of doomed matter as it orbited a
black hole four times, an observational first. Their
technique provides a new method to measure the mass of
a black hole; and this may enable the testing of
Einstein’s theory of gravity to a degree few thought
possible.

A team led by Dr. Kazushi Iwasawa at the Institute of
Astronomy (IoA) in Cambridge, England, followed the
trail of hot gas over the course of a day as it
whipped around the supermassive black hole roughly at
the same distance the Earth orbits the Sun. Quickened
by the extreme gravity of the black hole, however, the
orbit took about a quarter of a day instead of a year.

The scientists could calculate the mass of the black
hole by plugging in the measurements for the energy of
the light, its distance from the black hole, and the
time it took to orbit the black hole — a marriage of
Einstein’s general relativity and good old-fashioned
Keplerian physics.

Iwasawa and his colleague at the IoA, Dr. Giovanni
Miniutti, present this result today during a Web-based
press conference in New Orleans at the meeting of the
High Energy Astrophysics Division of the American
Astronomical Society. Dr. Andrew Fabian of the IoA
joins them on an article appearing in an upcoming
issue of the Monthly Notices of the Royal Astronomical
Society. The data is from the European Space Agency’s
XMM-Newton observatory.

The team studied a galaxy named NGC 3516, about 100
million light years away in the constellation Ursa
Major, home to the Big Dipper (or, the Plough). This
galaxy is thought to harbour a supermassive black hole
in its core. Gas in this central region glows in
X-ray radiation as it is heated to millions of degrees
under the force of the black hole’s gravity.

XMM-Newton captured spectral features from light
around the black hole, displayed on a spectrograph
with spikes indicating certain energy levels, similar
in appearance to the jagged lines of a cardiograph.
During the daylong observation, XMM captured a flare
from excited gas orbiting the black hole as it whipped
around four times. This was the crucial bit of
information needed to measure the black hole mass.

The scientists already knew the distance of the gas
from the black hole from its spectral feature. (The
extent of gravitational redshift, or energy drain
revealed by the spectral line, is related to how close
an object is to a black hole.) With an orbital time
and distance, the scientists could pin down a mass
measurement — between 10 million and 50 million solar
masses, in agreement with values obtained with other
techniques.

While the calculation is straightforward, the analysis
to understand the orbital period of an X-ray flare is
new and intricate. Essentially, the scientists
detected a cycle repeated four times: a modulation in
the light’s intensity accompanied by an oscillation in
the light’s energy. The energy and cycle observed fit
the profile of light gravitationally redshifted
(gravity stealing energy) and Doppler shifted (a gain
and loss in energy as orbiting matter moves towards
and away from us).

The analysis technique implies, to this science team’s
surprise, that the current generation of X-ray
observatories can make significant gains in measuring
black hole mass, albeit with long observations and
black hole systems with long-lasting flares. Building
upon this information, proposed missions such as
Constellation-X or XEUS can make deeper inroads to
testing Einstein’s math in the laboratory of extreme
gravity.

A fuller explanation of this result, including the
analysis technique, is available at:
An image of galaxy NGC 3516 and an artist’s impression
of a black hole surrounded by an accretion disc can be
downloaded from:
http://universe.nasa.gov/press/iwasawa/

CONTACTS:

Dr Kazushi Iwasawa, Dr Giovanni Miniutti and Dr Andy
Fabian

Institute of Astronomy, University of Cambridge,

Madingley Road, Cambridge, CB3 0HA, UK

Tel: +44 (0)1223 337548 or 337509

E-mail (Dr Iwasawa): ki@ast.cam.ac.uk

E-mail (Dr Fabian): acf@ast.cam.ac.uk

AAS High Energy Astrophysics Meeting Pressroom, New
Orleans:
Tel: +1 504 681 4481

NOTES FOR EDITORS

IMAGE CAPTIONS:

IMAGE 1: Seyfert I galaxy NGC 3516, as seen in
optical light with the Hubble Space Telescope. The
observation by Iwasawa et al. is of a region no larger
than our Solar System within this galaxy — by scale,
a mere pinpoint within the center of this HST image.
The Iwasawa et al. observation relied on spectroscopy,
however, not imaging. Credit: HST/UCLA/M. Malkan

IMAGE 2: An artist’s concept of a black hole,
surrounded by an accretion disk. The gas in the
accretion disc is heated to millions of degrees and
emits X-ray radiation, particularly close to the black
hole. The black hole’s event horizon, it’s
theoretical border, is represented here as a black
sphere, although a black hole has no surface.

INSTITUTE OF ASTRONOMY

The Institute of Astronomy is a department of the
University of Cambridge and is engaged in teaching and
research in the fields of theoretical and
observational Astronomy.

FACTS ABOUT XMM

XMM-Newton can detect more X-ray sources than any
previous observatory and is helping to solve many
cosmic mysteries of the violent Universe, from black
holes to the formation of galaxies. It was launched on
10 December 1999, using an Ariane-5 rocket from French
Guiana. It is expected to return data for a decade.
XMM-Newton’s high-tech design uses over 170 wafer-thin
cylindrical mirrors spread over three telescopes. Its
orbit takes it almost a third of the way to the Moon,
so that astronomers can enjoy long, uninterrupted
views of celestial objects.

SpaceRef staff editor.