Astronomers discover an unusual cosmic lens

Jul 16, 2010
These images of the first-ever foreground quasar (blue) lensing a background galaxy (red) were taken with the Keck II telescope using laser guide-star adaptive optics. Credit: Courbin, Meylan, Djorgovski, et al., EPFL/Caltech/WMKO.

Astronomers at the California Institute of Technology (Caltech) and Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have discovered the first known case of a distant galaxy being magnified by a quasar acting as a gravitational lens. The discovery, based in part on observations done at the W. M. Keck Observatory on Hawaii's Mauna Kea, is being published July 16 in the journal Astronomy & Astrophysics.

Quasars, which are extraordinary luminous objects in the distant universe, are thought to be powered by supermassive black holes in the cores of galaxies. A single quasar could be a thousand times brighter than an entire galaxy of a hundred billion stars, which makes studies of their host galaxies exceedingly difficult. The significance of the discovery, the researchers say, is that it provides a novel way to understand these host galaxies.

"It is a bit like staring into bright car headlights and trying to discern the color of their rims," says Frédéric Courbin of EPFL, the lead author on the paper. Using gravitational lensing, he says, "we now can measure the masses of these quasar host galaxies and overcome this difficulty."

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 galaxy, the part of the light that comes from the galaxy will split. Because of this, an observer on Earth will see two or more close images of the now-magnified background galaxy.

The first such gravitational lens was discovered in 1979, and produced an image of a distant quasar that was magnified and split by a foreground galaxy. Hundreds of cases of gravitationally lensed quasars are now known. But, until the current work, the reverse process—a background galaxy being lensed by the massive host galaxy of a foreground quasar—had never been detected.

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EPFL and Caltech researchers have discovered a quasar acting as a cosmic lens, magnifying a 7.5 light year distant galaxy. Video by EPFL.

Using gravitational lensing to measure the masses of distant galaxies independent of their brightness was suggested in 1936 by Caltech astrophysicist Fritz Zwicky, and the technique has been used effectively for this purpose in recent years. Until now, it had never been applied to measure the masses of quasar hosts themselves.

To find the cosmic lens, the astronomers searched a large database of quasar spectra obtained by the Sloan Digital Sky Survey (SDSS) to select candidates for "reverse" quasar-galaxy gravitational lensing. Follow-up observations of the best candidate—quasar SDSS J0013+1523, located about 1.6 billion light years away—using the W. M. Keck Observatory's 10-meter telescope, confirmed that the quasar was indeed magnifying a , located about 7.5 billion light years away.

Astronomers discover an unusual cosmic lens
These images of the first-ever foreground quasar (blue) lensing a background galaxy (red) were taken with the Keck II telescope using laser guide-star adaptive optics. Credit: Courbin, Meylan, Djorgovski, et al., EPFL/Caltech/WMKO.

"We were delighted to see that this idea actually works," says Georges Meylan, a professor of physics and leader of the EPFL team. "This discovery demonstrates the continued utility of as an astrophysical tool."

"Quasars are valuable probes of galaxy formation and evolution," says Professor of Astronomy S. George Djorgovski, leader of the Caltech team. Furthermore, he adds, "discoveries of more such systems will help us understand better the relationship between and the which contain them, and their coevolution."

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More information: Other coauthors of the Astronomy & Astrophysics paper, entitled "First case of strong gravitational lensing by a QSO: SDSS J0013+1523 at z = 0.120," are Malte Tewes and François Rerat of EPFL, Ashish Mahabal of Caltech, and Dominique Sluse of the Astronomical Research Institute in Heidelberg, Germany.

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User comments : 9

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nada
3 / 5 (6) Jul 16, 2010
I have to say this is the most poorly written article I have ever seen. Meandering on until finally in the sixth paragraph, a clue as to what the crap the author is talking about is put in the a sentence fragment of questionable composition "a background galaxy being lensed by the massive host galaxy of a foreground quasar"

The comment box instructions say "Brevity is the soul of wit." I wish the authors would apply the same rule as given to commenters.
ArcainOne
5 / 5 (5) Jul 16, 2010
I have to say this is the most poorly written article I have ever seen. Meandering on until finally in the sixth paragraph, a clue as to what the crap the author is talking about is put in the a sentence fragment of questionable composition "a background galaxy being lensed by the massive host galaxy of a foreground quasar"

The comment box instructions say "Brevity is the soul of wit." I wish the authors would apply the same rule as given to commenters.


"in Switzerland have discovered the first known case of a distant galaxy being magnified by a quasar acting as a gravitational lens."... litterally taken from the main title...
JustTheFacts
5 / 5 (3) Jul 16, 2010
"...the part of the light that comes from the galaxy will split. "

This couldn't be stated more incorrectly. There is no "splitting" of the light. There is only bending of light not originally moving toward us, causing us to see a trace of something that was otherwise obscured.
DoubleD
5 / 5 (2) Jul 16, 2010
"There is only bending of light not originally moving toward us"

Isnt it more appropriate to say that the light moves in a straight line, but spacetime is distorted ?
Skeptic_Heretic
2.3 / 5 (4) Jul 16, 2010
"...the part of the light that comes from the galaxy will split. "

This couldn't be stated more incorrectly. There is no "splitting" of the light. There is only bending of light not originally moving toward us, causing us to see a trace of something that was otherwise obscured.

Actually the light, as in all light originating from the obscured object, IS split around the quazar. In some cases you'll actually see multiple images of a single object due to gravitational lensing. This is similar to the effect seen in the dual slit experiment.
jonnyboy
3.7 / 5 (3) Jul 16, 2010
no, it isn't split. It IS photons that are originally going in one direction being redirected by the distortion of space time so that they end up coming at us.
SteWe
not rated yet Jul 17, 2010
The original paper:
http://arxiv.org/abs/1002.4991

Nothing is "split": Gravitation is a continuous field. Light passing through it is _not_ bend towards us at one point, and going straight on 5 milimeters to the left. Some people here seem to visualise gravitational lensing like this :
-----------
light -----------
-------%
SteWe
not rated yet Jul 17, 2010
Sadly, looks like the fancy ASCII graphics doesn't work out here :(
Anyhow, the lower "beam" suddenly getting a kink and going down would be wrong: Every "beam" would be slightly bend, the more the nearer one gets to the quasar galaxy.
Skeptic_Heretic
not rated yet Jul 17, 2010
Looks like we have us a bunch of people insisting on classical relativity and not applying quantum mechanics to complete the observation.