gravitational lens

(redirected from Bend light)
Also found in: Dictionary.
Gravitational lensingclick for a larger image
Gravitational lensing

gravitational lens

A concept arising from the fact that a gravitational field bends light, and hence a concentration of mass can focus light rays in a manner similar to that of a lens. In the illustration, the observer at O sees two apparent images S′ of the background source S caused by lensing effects of the intervening galaxy. The theory of gravitational lensing was discussed by both Einstein and Lodge in 1919, and its applications to cosmology realized by Zwicky in 1937, but the first known gravitational lens (the double quasar) was not discovered until 1979. Lensing by a smooth mass distribution such as a galaxy or a cluster of galaxies is known as macrolensing, and can occur in several forms.

The simplest form of gravitational lensing is where a pointlike background source, usually a quasar, is split into multiple images, the location and number of which are dependent on the relative geometry of the source and lens. The lens will distort and concentrate the original path of the light, so that an image will also appear brighter, or magnified. Different images forming a multiple system may have their luminosities magnified by different factors. Cases of double, triple and even quadruple lensing have been found (e.g. the Cloverleaf and the Einstein cross). In most cases the lensing galaxy is not observed. Theoretical models of gravitational lensing predict that there should always be an odd number of images so both the double and quadruple systems are expected to have a central image that is too faint to be detected.

If the background object is a distant galaxy that is itself extended, the lensed images are smeared out into long luminous arcs several arc seconds long. Such arcs are commonly observed in the core of rich clusters of galaxies, usually elongated tangentially to the cluster center and bluer in color than the cluster member galaxies. In several clusters many tens of smaller arclets are seen, which originate from weak lensing of background galaxies that are not so strongly magnified. The most extreme case of gravitational lensing is observed when an extended background source is exactly aligned with a symmetrical lens. The lensed image takes the form of an Einstein ring.

The alteration in the light path to the quasar will result in different times of flight for each image. If the quasar itself is variable, then a corresponding time delay for the brightening to be seen in each component of the image may be measured. The difference in the light travel time is related to the inverse of the Hubble constant, so it is theoretically possible to estimate H 0 from such time delays. In practice, precise modeling of the lens geometry is required before H 0 can be well constrained.

It is possible that individual stars in a lensing galaxy can cross the light path to the quasar and cause fluctuations in image brightness known as microlensing. This effect can also be seen when objects known as MACHOs in the galactic halo lens the light from an extragalactic star to cause a large amplification in its brightness, although such events are very rare.

gravitational lens

[‚grav·ə′tā·shən·əl ′lenz]
A massive galaxy or other massive object whose gravitational field focuses light from a distant quasar near or along its line of sight, giving a double or multiple image of the quasar.
References in periodicals archive ?
First, lens edges scatter light, partly because they're held inside a circular mount and some light hits the mount, and partly because lens edges must bend light at a steeper angle than light entering near the middle of the lens.
Both lenses and diffraction gratings bend light at different wavelengths to different extents, what scientists call "chromatic aberration," that can be overcome in conventional optics through use of a series of lenses that correct for that.
The researchers discovered that photonic meta-materials, made up of very small rods just a few hundred nanometres across that are arranged into a structure resembling a woodpile, could be carefully arranged so that they are able to partially bend light waves.
Crandall used phased zone plates to bend light without a loss of brightness, allowing the MicroSight to be used without any additional equipment.
One of the most exciting applications is an electromagnetic cloak that can bend light around itself, similar to the flow of water around a stone," said Hammond.
Metamaterials allow the scientists to bend light so shadows and reflections don't appear.
Materials created by researchers in the US can bend light around three dimensional objects so they seem to disappear.
Mathematicians in Finland are developing "wormholes" using exotic nanomaterials that bend light around objects; the light from planar displays of pixels would travel invisibly through the cloaking wormhole tunnel to their fixed position in space, thus creating a floating 3-D image.
Which component parts of binoculars bend light travelling between the lenses?
The cloak would achieve the same effect as in JK Rowling's blockbuster using special materials that bend light, rather than spells.
They're thinking that] you really shouldn't be able to bend light or fly.
Bend light around corners, stop time with a pair of sunglasses, pour light into the palm of your hand, or even make your small TV project a large-screen image.