Up Close and Personal
with a Gravitational Lens
Amid the thousands
of galaxies in this galaxy field
- one stands out as different that the others.
Notice the dramatic blue
arc in the center of the detail photo below.
"The blue arc is an image of a distant galaxy
that has been smeared into the odd shape by a
phenomenon called gravitational lensing. This
"funhouse- mirror effect" occurs when
light from a distant object is bent and stretched
by the mass of an intervening object. In this
case the gravitational lens, or intervening object,
is a red elliptical galaxy nearly 6 billion light-years
from Earth. The red color suggests that the galaxy
contains older, cooler stars.
The distant object whose image is smeared into
the long blue arc is about 10 billion light-years
away. This ancient galaxy existed just a few billion
years after the Big Bang, when the universe was
about a quarter of its present age. The blue color
indicates that the galaxy contains hot, young
Gravitational lenses can be seen throughout the
sky because the cosmos is crowded with galaxies.
Light from distant galaxies, therefore, cannot
always travel through space without another galaxy
getting in the way. It is like walking through
a crowded airport. In space, a faraway galaxy's
light will travel through a galaxy that is in
the way. But if the galaxy is massive enough,
its gravity will bend and distort the light.
Long arcs, such as the one in this image, are
commonly seen in large clusters of galaxies because
of their huge concentrations of mass. But they
are not as common in isolated galaxies such as
this one. For the gravitational lens to occur,
the galaxies must be almost perfectly aligned
with each other.
Gravitational lenses yield important information
about galaxies. They are a unique and extremely
useful way of directly determining the amount
of mass, including dark matter, in a galaxy. Galaxies
are not just made up of stars, gas, and dust.
An invisible form of matter, called dark matter,
makes up most of a galaxy's mass. Studies of this
galaxy, together with similar observations, may
allow astronomers to make the first direct measurements
of the masses of bright, nearby galaxies."
Visit the STScI
Website for more information on this gravitational