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Astronomers have been using optical telescopes for over four centuries.
But they like thinking out of the box, and innovation has
taken astronomy far beyond its historical realm of visible wavelengths.
In the history of astronomy, there have really only been two major revolutions in
the way we view the universe.
The first was the invention of the telescope,
first used systematically by Galileo to observe the night sky,
and subsequent to that the le, gradual growth in the size of
collecting area to gain this factor of ten billion in depth over the naked eye.
The second revolution in astronomy, equally important, was the levering open
of the electromagnetic spectrum by technologies that allowed us to detect.
Radio waves, infrared waves, x-rays, gamma rays, and
ultraviolet radiation, often from the same astrophysical object.
These technologies took awhile to be worked into serious and
mature radio facilities, x-ray facilities, and gamma ray facilities.
But now we have ways to probe the universe across the full range of
the electromagnetic spectrum.
Perhaps the final frontier in this history would be opening up the universe to
gravity waves, which essentially give us gravity eyes and
let us see the mass of the universe directly.
Remember that electromagnetic radiation is sometimes an indirect way of
seeing the universe.
Because it depends on the ways that light reflects, refracts, and
emits from normal matter.
We don't see the matter itself.
With gravity waves, we would see the stuff of the universe directly, and
this may be the final frontier in astronomy.
As a prelude to seeing the stuff of the universe,
astronomers have experimented with using the universe itself as a telescope.
Einstein's General Theory of Relativity contained a core prediction that
mass would bend space and that light would follow the contours of space and
so be bent by matter.
This is called gravitational lensing.
The gravitational lensing effect,
where mass literally acts a way an optical lens would by focusing and
magnifying and distorting radiation, has been observed now thousands of times.
The typical situation would be when a massive cluster of
galaxies containing the equivalent of perhaps ten to the power of 15 stars,
sits between us and more distant galaxies.
That huge concentration of matter bends light such that the distant
galaxies appear magnified, amplified, and distorted by the foreground cluster.
The cluster is acting essentially as a lens.
The lensing effect,
the amount of the deflection, is a key to how much mass that cluster contains.
So this is a way of weighing the universe or objects within it.
A simulation shows the effect.
The foreground lensing object is made of massive red galaxies like
elliptical galaxies.
The background more distant young galaxies are blue, and their light is sheared and
distorted into miniature arcs.
These little arcs which exist in fragments that form concentric circles around
the center of the mass distribution causing the lensing is
a classic signature of lensing, cannot be mistaken for any other phenomenon.
In a simulation it's easy to show what would happen if we moved the lens across
the sky and observe its distorting effect on different background galaxies.
Hubble Space Telescope was the first facility that showed this
effect strongly and clearly with its exquisite imaging, and
Hubble itself has now seen this effect hundreds of times.
A single deep image of a cluster of galaxies with the Hubble Space Telescope
shows the dozens of red, relatively nearby galaxies in the cluster.
And literally hundreds of distant background galaxies,
more blue, that are distorted into tiny little fragments and arcs.
Each of these little distorted fragments is like a ray tracing in
an optical diagram, and this entire configuration gives us
a wonderful measurement in the mass distribution of that's object,
the cluster of galaxies causing the lensing.
Along the way, of course, we're confirming Einstein's general theory of
relativity since this was a core prediction of the theory that was
unobserved when Einstein made the prediction.
Astronomers have moved beyond vision to new ways of seeing the universe.
The first was just an assistance to the eye.
The optical telescope.
Larger and larger gathering power to amplify what the eye could see.
More profound was the revolution that opened up the electro magnetic spectrum.
A factor of a trillion in wavelength.
And more recent is the prospect of looking at the universe in terms of its mass.
Either by the detection of gravity waves, or by the use of the tele,
the universe as a telescope, through the gravitational lensing effect.
Chris ImpeyDistinguished Professor
