This labeled image of the first-ever foreground quasar (blue) lensing a background galaxy (red) was taken with the Keck II telescope and its NIRC-2 instrument using laser guide star adaptive optics. Discovering more of these lenses will allow astronomers to determine the masses of quasars’ host galaxies.
Credit: F. Courbin/S. G. Djorgovski/G. Meylan/Caltech/EPFL/WMKO
A giant black hole spouting energy from inside a galaxy is acting like a cosmic magnifying glass, giving astronomers a clear view of an even more distant galaxy behind it.
It is the first time a quasar ? the central region of a galaxy dominated by an energy-spewing black hole ? has been discovered acting as a gravitational lens. The cosmic lens phenomenon was first predicted by Albert Einstein's theory of general relativity.
The discovery gives astronomers a glimpse at two galaxies at once, allowing researchers to photograph the distant object while weighing and measuring the intervening galaxy and the bright powerhouse at its core.
The quasar is known as SDSS J0013+1523 and located about 1.6 billion light-years from Earth.
According to the theory, very large masses warp the space-time around them, even causing light to bend as it travels through the region. Thus, light from faraway objects sometimes can be magnified by the bent space-time to provide a larger and brighter ? though also distorted and curved ? view.
In this case, scientists are more interested in studying the lens itself than the magnified image.
Galaxies that host quasars are hard to study because their light is often overpowered by the blaring radiation from material falling onto the supermassive black holes in their centers. A single quasar can be 1,000 times brighter than an entire galaxy of 100 billion stars.
"It is a bit like staring into bright car headlights and trying to discern the color of their rims," lead researcher Fr?d?ric Courbin of the Ecole Polytechnique F?d?rale de Lausanne in Switzerland said in a statement. By studying the way a quasar magnifies light as a gravitational lens, he said, "we now can measure the masses of these quasar host galaxies and overcome this difficulty."
The newfound lens, and similar ones being sought by researchers, could provide an opportunity to learn about the galaxies that shelter quasars in their centers.
By studying the way the quasar magnifies the distant light ? including the shape of its distortion and the number of magnified images the lens produces ? scientists can measure how matter is distributed in the lens galaxy. They can even calculate the total matter of the quasar and its host galaxy.
Often quasars are discovered when their light is being magnified by an intervening galaxy acting as a gravitational lens. Scientists set out to look for a case of this reverse lensing of a galaxy's light by a quasar by looking through the data obtained by the Sloan Digital Sky Survey ? a detailed map of a quarter of the sky.
It was through that study that researchers found the quasar SDSS J0013+1523 acting as a cosmic lens.
"We were delighted to see that this idea actually works," said Georges Meylan, a professor of physics at Ecole Polytechnique F?d?rale de Lausanne."This discovery demonstrates the continued utility of gravitational lensing as an astrophysical tool."
The researchers published their findings July 20 in the journal Astronomy & Astrophysics.
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