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Five Images of a Quasar Viewed through a Gravitational Lens
NASA's Hubble Space Telescope has captured the first-ever picture of a group of five star-like images of a single distant quasar. These
images are seen in the above picture as four bright, white spots near the center
of the image and one smaller white spot seen through the large orange galaxy at
the center of the image. The multiple-image effect is produced by a process called
lensing, in which the gravitational field of a massive object—in this case, a cluster of galaxies—bends and amplifies light from an object—in this case, a quasar—farther behind it.
Although many examples of gravitational lensing have been observed, this "quintuple quasar" is the only case so far in which multiple quasar images are produced by an entire galaxy cluster acting as a gravitational lens.
A quasar is the brilliant core of a galaxy. It is powered by a super-massive black hole that is devouring gas and dust and creating a gusher of light in the process. When the quasar's light passes through the gravity field of the galaxy cluster that lies between us and the quasar, the light is bent by the space-warping gravity field in such a way that five separate images of the object are produced surrounding the cluster's center. The fifth quasar image is embedded to the right of the core of the central galaxy in the cluster. The cluster also creates a cobweb of images of other distant galaxies gravitationally lensed into arcs.
The galaxy cluster creating the lens is known as SDSS J1004+4112 and was discovered in the Sloan Digital Sky Survey. It is one of the more distant clusters known (seven billion light-years away), and is seen as it appeared when the universe was half its present age.
Spectral data taken with the Keck I 10-meter telescope show that the five quasar images are images of the same galaxy. The spectral results match those inferred by a lens model based only on the image positions and measurements of the light emitted from the quasar.
A gravitational lens will always produce an odd number of lensed images, but one image—the one bent the least— is usually very weak and embedded deep within the light of the lensing object itself. Though previous observations of SDSS J1004+4112 have revealed four of the images of this system, Hubble's sharp vision and the high magnification of this gravitational lens combine to place a fifth image far enough from the core of the central imaging galaxy to make it visible as well.
The galaxy hosting the background quasar is at a distance of 10 billion light-years, providing a glimpse of the convulsive evolution of galaxies when the universe was a quarter of its present age. The host galaxy can be seen in the image as multiple faint red arcs about the four white spots. This is the most highly magnified quasar host galaxy ever seen.
The Hubble picture also shows a large number of stretched arcs that are more distant galaxies lying behind the cluster, each of which is split into multiple distorted images.