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Large Telescopes Team Up to Help Astronomers Discover a Trio ofQuasars (Forwarded)



 
 
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Old January 9th 07, 04:24 AM posted to sci.astro
Andrew Yee
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Default Large Telescopes Team Up to Help Astronomers Discover a Trio ofQuasars (Forwarded)

ESO Education and Public Relations Dept.

Contacts:

Georges Meylan
Ecole Polytechnique Fédérale de Lausanne
Phone (Sauverny): +41 22 379 24 25
Phone (Lausanne): +41 21 693 06 44

S. George Djorgovski
(attending the AAS meeting in Seattle on Jan. 7-8)
Caltech Astronomy, USA
Phone: +1 (626) 395-4415

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For Immediate Release: 8 January 2007

ESO 02/07

It Is No Mirage!

Large Telescopes Team Up to Help Astronomers Discover a Trio of Quasars

Using ESO's Very Large Telescope and the W.M. Keck Observatory,
astronomers at the Ecole Polytechnique Fédérale de Lausanne in Switzerland
and the California Institute of Technology, USA, have discovered what
appears to be the first known triplet of quasars. This close trio of
supermassive black holes lies about 10.5 billion light-years away towards
the Virgo (The Virgin) constellation.

"Quasars are extremely rare objects," says George Djorgovski, from Caltech
and leader of the team that made the discovery. "To find two of them so
close together is very unlikely if they were randomly distributed in
space. To find three is unprecedented."

The findings are being reported at the winter 2007 meeting of the American
Astronomical Society in Seattle, USA.

Quasars are extraordinary luminous objects in the distant universe,
thought to be powered by supermassive black holes at the heart of
galaxies. A single quasar could be a thousand times brighter than an
entire galaxy of a hundred billion stars, and yet this remarkable amount
of energy originates from a volume smaller than our solar system. About a
hundred thousand quasars have been found to date, and among them several
tens of close pairs, but this is the first known case of a close triple
quasar system.

Quasars (QUAsi StellAR Sources) were first discovered in 1963 by the
Dutch-American astronomer Maarten Schmidt at the Palomar Observatory
(California, USA) and the name refers to their 'star-like' appearance on
the images obtained at that time. Distinguishing them from stars is thus
no easy task and discovering a close trio of such objects is even less
obvious.

The feat could only be accomplished by combining images from two of the
largest ground-based telescopes, ESO's 8.2-m Very Large Telescope at Cerro
Paranal, in Chile, and the W. M. Keck Observatory's 10-m telescope atop
Mauna Kea, Hawaii, as well as using a very sophisticated and efficient
image sharpening method.

The distant quasar LBQS 1429-008 was first discovered in 1989 by an
international team of astronomers led by Paul Hewett of the Institute of
Astronomy in Cambridge, England. Hewett and his collaborators found a
fainter companion to their quasar, and proposed that it was a case of
gravitational lensing. According to Einstein's general theory of
relativity, if a large mass (such as a big galaxy or a cluster of
galaxies) is placed along the line of sight to a distant quasar, the light
rays are bent, and an observer on Earth will see two or more close images
of the quasar -- a cosmic mirage. The first such gravitational lens was
discovered in 1979, and hundreds of cases are now known. However, several
groups over the past several years cast doubts that this system is a
gravitational lens, and proposed instead that it is a close physical pair
of quasars.

What the Caltech-Swiss team has found is that there is a third, even
fainter quasar associated with the previously known two. The three quasars
have the same redshift, hence, are at the same distance from us.

The astronomers performed an extensive theoretical modeling, trying to
explain the observed geometry of the three images as a consequence of
gravitational lensing. "We just could not reproduce the data," says
Frédéric Courbin of Lausanne. "It is essentially impossible to account for
what we see using reasonable gravitational lensing models."

Moreover, there is no trace of a possible lensing galaxy, which would be
needed if the system were a gravitational lens. The team has also
documented small, but significant differences in the properties of the
three quasars. These are much easier to understand if the three quasars
are physically distinct objects, rather than gravitational lensing
mirages. Combining all these pieces of evidence effectively eliminated
lensing as a possible explanation.

"We were left with an even more exciting possibility that this is an
actual triple quasar," says Georges Meylan, also from Lausanne. The three
quasars are separated by only about 100,000 to 150,000 light-years, which
is about the size of our own Milky Way.

Gravitational lensing can be used to probe the distribution of dark and
visible mass in the universe, but quasar pairs -- and now a triplet --
provide astronomers with a different kind of insight.

"Quasars are believed to be powered by gas falling into supermassive black
holes," says Djorgovski. "This process happens very effectively when
galaxies collide or merge, and we are observing this system at the time in
the cosmic history when such galaxy interactions were at a peak."

If galaxy interactions were responsible for the quasar activity, having
two quasars close together would be much more likely than if they were
randomly distributed in space. This may explain the unusual abundance of
binary quasars, which have been reported by several groups. "In this case,
we are lucky to catch a rare situation where quasars are ignited in three
interacting galaxies," says Ashish Mahabal, one of the Caltech scientists
involved in the study.

Discoveries of more such systems in the future may help astronomers
understand better the fundamental relationship between the formation and
evolution of galaxies, and the supermassive black holes in their cores,
now believed to be common in most large galaxies, our own Milky Way
included.

This work is also described in a paper submitted to the Astrophysical
Journal Letters. The team is composed of S. George Djorgovski, Ashish
Mahabal, and Eilat Glikman of Caltech (USA), Frédéric Courbin, Georges
Meylan and Dominique Sluse of the Ecole Polytechnique Fédérale de Lausanne
(Switzerland), and David Thompson of the University of Arizona's Large
Binocular Telescope Observatory (USA).

National contacts for the media:

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Finland: Ms. Riitta Tirronen, +358 9 7748 8369
Denmark: Dr. Michael Linden-Vřrnle, +45-33-18 19 97
France: Dr. Daniel Kunth, +33-1-44 32 80 85
Germany: Dr. Jakob Staude, +49-6221-528229
Italy: Dr. Leopoldo Benacchio, +39-357-230 26 51
The Netherlands: Ms. Marieke Baan, +31-20-525 74 80
Portugal: Prof. Teresa Lago, +351-22-089 833
Sweden: Dr. Jesper Sollerman, +46-8-55 37 85 54
Switzerland: Dr. Martin Steinacher, +41-31-324 23 82
United Kingdom: Mr. Peter Barratt, +44-1793-44 20 25

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