Transcript Gravitational Lensing

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
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When Eddington observed the 1919 eclipse, he could
have 3 results:
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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
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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.
Bibliography
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http://images.google.com/imgres?imgurl=http://www.ams.org/featurecolumn/images/HSTgravlens.jpg&imgrefurl=ht
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http://www.jpl.nasa.gov/releases/2004/103a.cfm
www.nsf.gov
http://en.wikipedia.org/wiki/Einstein_ring