Gravitational Lensing By: Shawn Carney

What is Gravitational Lensing? Gravitational lensing is a visual effect caused by the distortion of space-time caused by large masses. The paths that light follow no longer remain straight.

History General Relativity: Explain the orbit of Mercury Gravitational redshifting Gravitational lensing Einstein’s Theory of relativity was proved by Arthur Eddington in 1919 with the viewing of lensing around the Sun of the Hyades.

Einstein v Newton Angle of deflection: Θ=4GM/bc2 When Eddington observed the 1919 eclipse, he could have 3 results: NO lensing .87 arc seconds of lensing 1.74 arc seconds of lensing Angle of deflection: Θ=4GM/bc2

Effects and Applications of lensing The Einstein Cross Arcs and rings Images are amplified in intensity Time delays Distance calculations Ability to calculate lens mass

Einstein Cross For this effect, the lensing is so great, the original image is multiplied, usually to two or four images. These images are usually also magnified. This specific image is a quasar located about 8 billion light years from Earth, and the lensing galaxy is located about 400 million light years from earth. Only Two of these occurances have ever been observed.

Microlensing Microlensing is a lensing effect caused by fore-ground stars or planets. While the lensing is much less than that caused by a galaxy, microlensing can greatly magnify the original source. This effect can also increase the ability to study the lens’s composition. http://www.jpl.nasa.gov/videos/microlensing/mag4.mov

Weak Gravitational lensing Also known as the Einstein rings. Most commonly made by light from other galaxies or quasars passing by a galaxy cluster. This form of lensing creates multiple arcs and even rings of the source galaxy. The size of an Einstein ring in radians is denoted by:

Time Delay Because images follow different paths, light from stellar objects can reach Earth several days, or even years before other photons from the same instance do. This allows for observers a second chance viewing for which they are prepared, most significantly for explosive events. This time delay also allows for distance calculation to the lensing galaxy or cluster.

Distance calculation A result of the time delay aspect caused by lensing, absolute distances can be calculated to distant objects. This holds great significance as it allows for the calculation of the Hubble constant, the expansion rate of the universe.

Mass calculation Because the angle of deflection can be measured, the mass of the lens can be calculated. Discrepencies between this mass and the mass predicted by the luminosity of the lens are accounted for by dark matter.

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