ESA's Integral discovers hidden black holes (Forwarded)

European Space Agency
Science New Release SNR 21-2003
Paris, France 17 October 2003

ESA's Integral discovers hidden black holes

Integral, ESA's powerful gamma-ray space telescope, has discovered what seems to
be a new class of astronomical objects. These are binary systems, probably
including a black hole or a neutron star, embedded in a thick cocoon of cold
gas. They have remained invisible so far to all other telescopes. Integral was
launched exactly one year ago today to study the most energetic phenomena in the
universe.

Integral detected the first of these objects, called IGRJ16318-4848, on 29
January 2003. Although astronomers did not know its distance, they were sure it
was in our Galaxy. Also, after some analysis, researchers concluded that the new
object could be a binary system comprising a compact object, such as a neutron
star or a black hole, and a very massive companion star.

When gas from the companion star is accelerated and swallowed by the more
compact object, energy is released at all wavelengths, from the gamma rays
through to visible and infrared light. About 300 binary systems like those are
known to exist in our galactic neighbourhood and IGRJ16318-4848 could simply
have been one more. But something did not fit: why this particular object had
not been discovered so far?

Astronomers, who have been observing the object regularly, guess that it had
remained invisible because there must be a very thick shell of obscuring
material surrounding it. If that was the case, only the most energetic radiation
from the object could get through the shell; less-energetic radiation would be
blocked. That could explain why space telescopes that are sensitive only to
low-energy radiation had overlooked the object, while Integral, specialised in
detecting very energetic emissions, did see it.

To test their theory, astronomers turned to ESA's XMM-Newton space observatory,
which observes the sky in the X-ray wavelengths. As well as being sensitive to
high-energy radiation, XMM-Newton is also able to check for the presence of
obscuring material. Indeed, XMM-Newton detected this object last February, as
well as the existence of a dense 'cocoon' of cold gas with a diameter of similar
size to that of the Earth's orbit around the Sun.

This obscuring material forming the cocoon is probably 'stellar wind', namely
gas ejected by the supermassive companion star. Astronomers think that this gas
may be accreted by the compact black hole, forming a dense shell around it. This
obscuring cloud traps most of the energy produced inside it.

The main author of these results, Roland Walter of the Integral Science Data
Centre, Switzerland, explained: "Only photons with the highest energies [above
10 keV] could escape from that cocoon. IGR J16318-4848 has therefore not been
detected by surveys performed at lower energies, nor by previous gamma-ray
missions that were much less sensitive than Integral."

The question now is to find out how many of these objects lurk in the Galaxy.
XMM-Newton and Integral together are the perfect tools to do the job. They have
already discovered two more new sources embedded in obscuring material. Future
observations are planned.

Christoph Winkler, ESA Project Scientist for Integral, said: "These early
examples of using two complementary ESA high-energy missions, Integral and
XMM-Newton, shows the potential for future discoveries in high-energy astrophysics."

Notes to Editors:

The paper explaining these results will be published in November in a special
issue of Astronomy and Astrophysics dedicated to Integral, on the occasion of
its first anniversary.

Integral

The International Gamma Ray Astrophysics Laboratory (Integral) is the first
space observatory that can simultaneously observe celestial objects in gamma
rays, X-rays and visible light. Integral was launched on a Russian Proton rocket
on 17 October 2002 into a highly elliptical orbit around Earth. Its principal
targets include regions of the galaxy where chemical elements are being produced
and compact objects, such as black holes.

XMM-Newton

XMM-Newton can detect more X-ray sources than any previous satellite 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.

Contacts:

Christoph Winkler
ESA ESTEC, The Netherlands
Tel: + 31 71 565 3591
E-mail:

Roland Walter
Integral Science Data Centre, Switzerland
Tel: + 41 22 950 91 28
E-mail:

For further information, please contact:

ESA Media Relations Service
Tel: +33 (0)1.53.69.71.55
Fax: +33 (0)1.53.69.76.90

Related articles

* Integral overview
http://www.esa.int/esaSC/120374_index_0_m.html
* XMM-Newton overview
http://www.esa.int/esaSC/120385_index_0_m.html

IMAGE CAPTIONS:

[Image 1:
http://www.esa.int/export/esaCP/SEMP..._index_1.html]
An artist's impression of the mechanisms in an interacting binary system. The
supermassive companion star (on the right-hand side) ejects a lot of gas in the
form of 'stellar wind'. The compact black hole orbits the star and, due to its
strong gravitational attraction, collects a lot of the gas. Some of it is
funnelled and accelerated into a hot disc. This releases a large amount of
energy in all spectral bands, from gamma rays through to visible and infrared.
However, the remaining gas surrounding the black hole forms a thick cloud which
blocks most of the radiation. Only the very energetic gamma rays can escape and
be detected by Integral.

[Image 2:
XMM-Newton spacecraft]
XMM-Newton spacecraft: Detecting the Universe's hot spots.

Credits: ESA. Illustration by Ducros

"Andrew Yee" wrote in message
news ....
Integral detected the first of these objects, called IGRJ16318-4848, on
29
January 2003. Although astronomers did not know its distance, they were
sure it
was in our Galaxy. Also, after some analysis, researchers concluded that
the new
object could be a binary system comprising a compact object, such as a
neutron
star or a black hole, and a very massive companion star.

Was there a direction for this system?

Looks like a possible candidate for Dark Matter, except that it does
certainly affect light directly...

David A. Smith

"dc" == dlzc@aol com \(formerly\) writes:

Integral detected the first of these objects, called
IGRJ16318-4848, on 29 January 2003. Although astronomers did not
know its distance, they were sure it was in our Galaxy. Also, after
some analysis, researchers concluded that the new object could be a
binary system comprising a compact object, such as a neutron star
or a black hole, and a very massive companion star.

dc Was there a direction for this system?

Yes, its name. The source is located at 16h 31.8m, -48d 48' (J2000).
This is in the constellation Norma. The spiral disk of the Milky Way
Galaxy runs through the constellation Norma, hence the comment in the
press release that this source is likely to be in the Galaxy.

dc Looks like a possible candidate for Dark Matter, except that it
dc does certainly affect light directly...

If they have uncovered a previously unknown class of objects, then,
yes, this would be a form of dark matter. However, it would be
baryonic dark matter, which from other observations (e.g., cosmic
nucleosynthesis) we already know is not the main form of dark matter.

--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

Dear Joseph Lazio:

"Joseph Lazio" wrote in message
...
"dc" == dlzc@aol com \(formerly\) writes:

Integral detected the first of these objects, called
IGRJ16318-4848, on 29 January 2003. Although astronomers did not
know its distance, they were sure it was in our Galaxy. Also, after
some analysis, researchers concluded that the new object could be a
binary system comprising a compact object, such as a neutron star
or a black hole, and a very massive companion star.

dc Was there a direction for this system?

Yes, its name. The source is located at 16h 31.8m, -48d 48' (J2000).
This is in the constellation Norma. The spiral disk of the Milky Way
Galaxy runs through the constellation Norma, hence the comment in the
press release that this source is likely to be in the Galaxy.

Thanks!

dc Looks like a possible candidate for Dark Matter, except that it
dc does certainly affect light directly...

If they have uncovered a previously unknown class of objects, then,
yes, this would be a form of dark matter. However, it would be
baryonic dark matter, which from other observations (e.g., cosmic
nucleosynthesis) we already know is not the main form of dark matter.

David A. Smith