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An international team1 , including
French astronomers from the Institut d’Astrophysique Spatiale (CNRS
- Université Paris 11, Orsay) and the Institut d’Astrophysique
de Paris (CNRS - Université Pierre et Marie Curie, Paris), have
just observed a very distant quasi-stellar object. Located approximately
12 billion light years away, this quasi-stellar object is subject to a
gravitational lensing phenomenon that amplifies its light and distorts
its image. Thanks to this phenomenon, the observation made with the Very
Large Array radio telescope network of the National Radio Astronomy Observatory
in New Mexico (United States) made it possible to reveal the presence
of a disk of molecular gas and dust around a massive black hole. This
disk is the center of intense stellar formation of over 900 solar masses
per year. This observation shows for the first time that the formation
of stars and that of a black hole take place at the same time. These results
are published in the review, Science, of April 4, 2003.
An international team of astronomers recently
observed the quasi-stellar object, PSS J2322+1944, with the "Very
Large Array" (VLA) radio telescope network of the National Science
Foundation, located in New Mexico (United States). This quasi-stellar
object is very distant, approximately 12 billion light years from the
Earth, and is one of the brightest quasi-stellar objects known. Optically
identified by G. Djorgovski (Caltech), PSS J2322+1944 was detected in
dust emission and then in the emission lines of the carbon monoxide molecule
(CO) by using the 30 m radio telescope and the Plateau de Bure interferometer
of the Institut de Radioastronomie Millimétrique, by Alain Omont
(IAP) and Pierre Cox (IAS). Thanks to the VLA, researchers were able to
obtain a radiation map of the CO molecule in this quasar. This observation
could be made with the VLA for the following two reasons:
- the quasi-stellar object being very distant, this carbon monoxide
line that is normally located in the millimetric wavelength radio band
is shifted towards lower frequencies by the Doppler effect. As a result,
the CO molecule can be observed in a centimetric wavelength band that
corresponds to the one covered by the VLA;
- this quasi-stellar object is subject to a gravitational lensing effect:
a galaxy located in the line of sight between us and the object amplifies
and distorts its image (gravitational mirage). In the case of this quasar,
the alignment between the lens and the source is almost perfect and
the resulting image is a ring known as a molecular Einstein ring, predicted
within the framework of the theory of relativity. The light from the
object and its immediate surroundings is amplified, thus making a detailed
study of the central regions of PSS J2322+1944 possible.
New observations reveal a gas and dust disk with
a radius of over 6,500 light years, surrounding the massive black hole.
This disk is the center of intense stellar formation with a production
rate estimated at approximately 900 solar masses per year, or a thousand
times more than in our galaxy.
Observations of "near" galaxies with a central black hole show
that they are also surrounded by gas and dust disks in which stars form,
although the quantities in question are much less than in the case of
PSS J2322+1944. On the basis of recent observations, it was possible to
show that there is a link between stellar formation, on one hand, and
the development of a massive central black hole, on the other, for these
local galaxies. Did these reactions take place when the universe was young,
at the time when the first galaxies were formed?
The discovery of intense stellar formation activity in a disk of matter
surrounding the massive black hole of PSS J2322+1944 shows that similar
processes effectively took place when the universe was only 10% as old
as it is today and, undoubtedly, the formation of black holes and stars
are phenomena that are very closely related.
In addition to this new possibility for observing the central region of
distant quasi-stellar objects, the use of the gravitational lensing phenomenon
opens new observation prospects. If the quasi-stellar object is subject
to light variations over a period of time, the multiple images formed
by gravitational lensing with have variations of intensity at different
moments in time. By measuring these time differences and with the help
of mathematical models, the distance of these objects could be measured
in a more precise way.
References:
A Molecular Einstein Ring: Imaging a Starburst Disk Surrounding a Quasi-Stellar
Object
C.L. Carelli, G.F. Lewis, S.G. Djorgovski and A. Mahabal, P. Cox, F. Bertoldi,
A. Omont, Science of
April 4, 2003
1 - This team includes:
C.L. Carelli of the National Radio Astronomy Observatory
G.F. Lewis of the University of Sydney
S.G. Djorgovski and A. Mahabal of the Califormia Institute of Technology
P. Cox of the Institut d’Astrophysique Spatiale (IAS)
F. Bertoldi of the Max-Planck Institut für Radioastronomie
A. Omont of the Institut d’Astrophysique de Paris (IAP)
Researcher contacts:
Pierre
Cox, Institut d’Astrophysique Spatiale.
Tel: +33 1 69 85 87 37. or at IRAM: +33 4 76 82 49 00
E-mail: Pierre.Cox@ias.u-psud.fr
CNRS-INSU contact:
Philippe Chauvin. Tel: +33 1 44 96 43 36
E-mail: philippe.chauvin@cnrs-dir.fr
Press contact:
Martine Hasler. Tel: +33 1 44 96 46 35
E-mail: martine.hasler@cnrs-dir.fr
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