GRAVITATIONAL LENSING Phys 43 SRJC Spring 2011 May 9, 2011 Roman Savinov Karan Kanagasabapathy Carlos Plascencia Attention! must be seen in the full screen mode. Hit below

GRAVITATIONAL LENSING What is Gravitational Lensing Types of Lensing Why do we care How these things are found

What is Gravitational Lensing Light does not always travel in straight lines… … massive objects deform the fabric of space itself... … when light passes one of these objets, such as a cluster of galaxies, its path is changed slightly.

What is Gravitational Lensing This effect is called gravitational lensing. It is only visible in rare cases and only the best telescopes can observe the related phenomena.

What is Gravitational Lensing

What is Gravitational Lensing simulation of gravitational lensing caused by a Schwarzschild black hole passing in front of a background galaxy. The surface brightness of the source image remains constant, but its angular size vary, hence producing an amplification of the galaxy luminosity as seen by a distant observer. Maximum amplification occurs when the galaxy (or in this case a bright part of it) is exactly behind the black hole. Unlike an optical lens, maximum 'bending' occurs closest to, and minimum 'bending' furthest from, the center of a gravitational lens. So lensing effect can magnify and distort the image of the background source. Hit Me

What is Gravitational Lensing Einstein Ring Gravitational Lens: SDSS J162746.44-005357.5 Einstein Ring Gravitational Lens: SDSS J120540.43+491029.3 If the distant galaxy, the lensing mass, and the observer lie in a straight line, the original galaxy will appear as a ring around the massive lensing object, called Einstein ring. If there is any misalignment the observer will see an arc segment instead.

Got it? What is Gravitational Lensing More commonly, when the lensing mass is complex (such as galaxy groups and clusters), the observer may then see multiple distorted images of the same source… …. the number and shape of these images depend upon the relative positions of the source, lens, and observer, and the shape of the gravitational well of the lensing object.

Types of Lensing Einstein Cross. Four images of the same distant quasar appear around a foreground galaxy due to strong gravitational lensing. Weak gravitational lensing causes many subtle shifts in the path of a light ray as it crosses the universe. This diagram shows the path of light from several galaxies (blue ovals at the back of the box) as it journeys toward us There are three classes of gravitational lensing Strong lensing: Weak lensing: Microlensing lensing effect that is strong enough to produce multiple images, arcs, or Einstein rings In this type of lensing the distortions of background sources are much smaller and can only be detected by analyzing large numbers of sources to find coherent distortions of only a few percent. Thus it is an intrinsically statistical measurement. Hit Me no distortion in shape can be seen but the amount of light received from a background object changes in time. The effect is small, which produces multiple images separated by only a few arcseconds

Why do we care A faint galaxy is outlined by a white ring in the shape of a sausage. The image is elongated due to the gravitational-lensing effect of a closer galaxy cluster. Abell 2218 Gravitational lenses can be used as gravitational telescopes. The concentrated light from objects seen behind gravitational lenses makes very faint objects appear brighter, larger and therefore more easily studied. One of the most distant object in the universe was discovered by the gravitational lensing effect. Hit Me Abell 2218 Abell 2218, a cluster of galaxies about 2 billion light-years away, was used as lens to see a galaxy some 13 billion years old This galaxy at the background of the Abell 2218 is seen from Earth as it would have been just 750 million years after the Big Bang.

Why do we care Observations of gravitational lensing can also be inverted to examine the lens itself. Gravitational lensing is particularly useful if the lens is for some reason difficult to see. Hit Me If the foreground lensing star has a planet, then that planet's own gravitational field can make a detectable contribution to the lensing effect. Gravitational lensing can probe the amount and distribution of mass. Hit Me Mass of the universe is dominated by invisible dark matter. The mass of lens’s constituent particles and their cross-section affect the distribution of dark matter in lens systems. Thus it is possible to determining how much dark matter they contain Next

If the foreground lensing star has a planet, then that planet's own gravitational field can make a detectable contribution to the lensing effect. Back

3D map of the large-scale distribution of dark matter, reconstructed from measurements of weak gravitational lensing with the Hubble Space Telescope. Back

How these things are found In the past most of the gravitational lenses have been discovered accidentally Today the search is done at 20 GHz frequency in the radio domain of the electromagnetic spectrum A big chunk of known lenses today were discovered by VLA -radio astronomy observatory in New Mexico The lensing is easier to detect and identify in simple objects compared to objects with complexity in them Very Large Array (VLA) - a radio astronomy observatory in New Mexico. Was used to discover most of the gravitational lenses known today.

Resources http://en.wikipedia.org/wiki/Gravitational_lens http://www.spacetelescope.org/science/gravitational_lensing/ http://dougintology.blogspot.com/2007/10/gravitational-lensing.html http://hetdex.org/dark_energy/how_find_it/gravitational_lensing.php http://en.wikipedia.org/wiki/Methods_of_detecting_extrasolar_planets