For the special case in which the source lies exactly behind
the lens (), due to the symmetry a ring-like image occurs whose angular
radius is called
Einstein radius
:
The Einstein radius defines the angular scale for a lens
situation. For a massive galaxy with a mass of
at a redshift of
and a source at redshift
, (we used here
as the value of the Hubble constant and an Einstein-deSitter
universe), the Einstein radius is
(note that for cosmological distances in general
!). For a galactic microlensing scenario in which stars in the
disk of the Milky Way act as lenses for bulge stars close to the
center of the Milky Way, the scale defined by the Einstein radius
is
An application and some illustrations of the point lens case can be found in Section 4.7 on galactic microlensing.
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Gravitational Lensing in Astronomy
Joachim Wambsganss http://www.livingreviews.org/lrr-1998-12 © Max-Planck-Gesellschaft. ISSN 1433-8351 Problems/Comments to livrev@aei-potsdam.mpg.de |