GRAVITATIONAL LENSINGGRAVITATIONAL LENSING

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Phys 43

SRJC

Spring 2011

May 9, 2011

Roman Savinov

Karan Kanagasabapathy

Carlos Plascencia

• What is Gravitational LensingWhat is Gravitational Lensing

• Types of LensingTypes of Lensing

• Why do we careWhy do we care

• How these things are foundHow these things are found

GRAVITATIONAL LENSINGGRAVITATIONAL LENSING

Light does not always travel in straight lines… 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.

… when light passes one of these objets, such as a cluster of galaxies, its path is changed slightly.

What is Gravitational LensingWhat is Gravitational Lensing

What is Gravitational LensingWhat is Gravitational Lensing

This effect is called 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.

It is only visible in rare cases and only the best telescopes can observe the related phenomena.

What is Gravitational LensingWhat is Gravitational Lensing

What is Gravitational LensingWhat is Gravitational Lensing

Unlike an optical lens, maximum 'bending' occurs closest to, and minimum 'bending' furthest from, the center of a gravitational lens.

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.So lensing effect can magnify and distort the image of the background source.

simulation of gravitational lensing simulation of gravitational lensing caused by a Schwarzschild black hole caused by a Schwarzschild black hole passing in front of a background passing in front of a background galaxy.galaxy.

simulation of gravitational lensing simulation of gravitational lensing caused by a Schwarzschild black hole caused by a Schwarzschild black hole passing in front of a background passing in front of a background galaxy.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.

What is Gravitational LensingWhat is Gravitational Lensing

If there is any misalignment the observer will see an arc segment instead.

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.

Einstein Ring Gravitational Lens: Einstein Ring Gravitational Lens: SDSS J120540.43+491029.3SDSS J120540.43+491029.3

Einstein Ring Gravitational Lens:

SDSS J162746.44-005357.5

What is Gravitational LensingWhat 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…

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.

…. 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.Got it?Got it?

Types of LensingTypes of Lensing

There are three classes of gravitational lensingThere are three classes of gravitational lensing

•Strong lensing: Strong lensing:

•Weak lensing:Weak lensing:

•MicrolensingMicrolensing

•Strong lensing: Strong lensing:

•Weak lensing:Weak lensing:

•MicrolensingMicrolensing

lensing effect that is strong enough to produce multiple images, arcs, or Einstein rings

Einstein Cross. Four images of the same distant quasar appear around a foreground galaxy due to strong gravitational lensing.

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.

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

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

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 careWhy do we care

Gravitational lenses can be used as gravitational telescopes. Gravitational lenses can be used as gravitational telescopes.

One of the most distant object in the universe was discovered by the gravitational lensing effect.

The concentrated light from objects seen behind gravitational lenses makes very faint objects appear brighter, larger and therefore more easily studied.

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.

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.

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

Abell 2218

Why do we careWhy do we care

Observations of gravitational lensing can also be inverted to examine the lens itself.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.

Gravitational lensing can probe the amount and distribution of mass.Gravitational lensing can probe the amount and distribution of mass.

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

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

Mass of the universe is dominated by invisible dark matter.

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

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

How these things are foundHow 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