Rubin Planetarium Video - Gravitational Lenses

A gravitational lens is an optical illusion produced when a concentration of mass, such as a galaxy or galaxy cluster, is located between the observer and a distant object, such as a galaxy or quasar. The intermediate concentration of mass serves as a lens, bending and magnifying the light of the distant object. The effect is explained by the general theory of relativity.

Gravitational lensing is a powerful tool used by astronomers to find and study dark matter. By measuring the shapes and locations of the gravitationally lensed images, it is possible to calculate the mass of the intermediate object. Using this technique, astronomers have been able to find dark matter inside galaxy clusters. Otherwise invisible, dark matter can be detected by the gravitational lensing it causes.

Currently only a couple dozen gravitational lenses are known to exist. LSST will find thousands more, ranging in size from single galaxies to giant galaxy clusters. These lenses will enable astronomers to better understand the distribution of dark matter throughout the Universe, which in turn will help us better understand the formation and the fate of the Universe.

Stroyboard

This animation illustrates gravitational lensing of distant galaxies caused by a foreground cluster. While astronomical images of this phenomenon are by necessity static snapshots, adding motion demonstrates the “lens” nature more effectively, as the viewer can follow the progress of background sources in and out of the lensing region. A number of bright blue galaxies in particular are easy to identify and follow. The lensing represented here comes primarily from the extended dark matter halo (not pictured) centered on the cluster and its largest central member (also known as the Brightest Cluster Galaxy or BCG). The lens distortion is shown mostly symmetric with some small perturbations caused by the asymmetric distribution of galaxies in the cluster. The filamentary structure visible over the entire dome represents the large-scale distribution of other galaxies throughout the Universe. Some parallax on these can be seen as our view rotates around the cluster. The lensing effect is shown to be strongest on the most distant/faintest galaxies, with progressively reduced distortion on closer objects in the background.

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A particularly dramatic distortion of a background galaxy can be seen here, creating multiple strongly-distorted images of the galaxy all around the cluster.

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A blue background source is distorted into a broken “Einstein ring” around the outer confines of the galaxy.

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Contact: Amanda Bauer, Head of LSST Education and Public Outreach abauer@lsst.org

Additional References

• https://www.symmetrymagazine.org/article/gravitational-lenses
• https://www.lsst.org/science/dark-matter
• https://www.lsst.org/sites/default/files/docs/aas/2010/215-RC-557-AAS_Marshall.pdf