Gravitational Lens Reveals Details Of Distant,
Ancient Galaxy
Image
1: This graphic shows a reconstruction (at lower
left) of the brightest galaxy, whose image has been
distorted by the gravity of a distant galaxy
cluster. The small rectangle in the center shows the
location of the background galaxy on the sky if the
intervening galaxy cluster were not there. The
rounded outlines show distinct, distorted images of
the background galaxy resulting from lensing by the
mass in the cluster. The image at lower left is a
reconstruction of what the lensed galaxy would look
like in the absence of the cluster, based on a model
of the cluster’s mass distribution derived from
studying the distorted galaxy images. Courtesy of
NASA; ESA; J. Rigby (NASA Goddard Space Flight
Center); K. Sharon (Kavli Institute for Cosmological
Physics); and M. Gladders and E. Wuyts (University
of Chicago)
Thanks to the presence of a natural
“zoom lens” in space, University of Chicago
scientists working with NASA’s Hubble Space
Telescope have obtained a uniquely close-up look at
the brightest gravitationally magnified galaxy yet
discovered.
The imagery offers a visually
striking example of gravitational lensing, in which
one massive object’s gravitational field can magnify
and distort the light coming from another object
behind it. Such optical tricks stem from Einstein’s
theory of general relativity, which describes how
gravity can warp space and time, including bending
the path that light travels.
In this case, gravity from the galaxy
cluster RCS2 032727-132623 bent and amplified the
light coming from a much more distant galaxy, 10
billion light-years from Earth. This “gravitational
telescope” creates a vast arc of light, as if the
distant galaxy had been reflected in a funhouse
mirror. The UChicago team reconstructed what the
distant galaxy really looks like, using
computational tools that reversed the effect of
gravitational lensing.
“What’s happening here is a
manifestation of general relativity,” said Michael
Gladders, assistant professor in astronomy &
astrophysics at UChicago. “Instead of seeing the
normal, faint image of that distant source, you see
highly distorted, highly magnified, and in this
case, multiple images of the source caused by the
intervening gravitational mass.”
The cosmic lens gave the UChicago
team the unusual opportunity to see what a galaxy
looked like 10 billion years ago. The reconstructed
image of the galaxy revealed regions of star
formation glowing like bright points of light. These
are much brighter than any star-formation region in
Earth’s home galaxy, the Milky Way.
‘Looking at the nature of dark matter’
In 2006 the Chicago astronomers used
the Very Large Telescope in Chile to measure the
arc’s distance and calculated that the galaxy
appears more than three times brighter than
previously discovered lensed galaxies. Then last
year, Jane Rigby of NASA’s Goddard Space Flight
Center in Greenbelt, Md., and the Chicago team
imaged the arc with the Hubble Space Telescope’s
Wide Field Camera 3.
Using this gravitational lens as a
telescope offers two major scientific opportunities,
Gladders said. First, “It gives us a look at that
very distant source with a precision and fidelity
that we couldn’t otherwise achieve,” he said.
And second, it provides an
opportunity to learn something about the
lens-forming mass, which is dominated by dark
matter. “It’s really a way of looking at the nature
of dark matter,” Gladders said. Dark matter accounts
for nearly 90 percent of all matter in the universe,
yet its identity remains one of the biggest
mysteries of modern science.
Keren Sharon, a postdoctoral scholar
at UChicago’s Kavli Institute for Cosmological
Physics, led the effort to perform a detailed
reconstruction of the lensed galaxy. She and her
co-authors, including Gladders, NASA’s Rigby and
UChicago graduate student Eva Wuyts, published their
findings last month in the Astrophysical Journal.
Sharon painstakingly created a
computer reconstruction of the gravitational lens,
then reverse-engineered the distorted image to
determine the distant galaxy’s actual appearance.
“It’s a little bit of an art, but there’s a lot of
physics in it. That’s the beauty of it,” Sharon
said. “It was a fun puzzle to solve, especially when
we had such great data.”
Gladders said Sharon is “one of the
world experts on exactly how to do this. Combine
that degree of finesse with this quality of data,
and you get a very nice result. This object now
becomes not only the brightest-lensed source known,
but because of this analysis, it is also going to be
one of the best-understood sources.”
Through spectroscopy, the spreading
out of light into its constituent colors, the team
plans to analyze the distant galaxy’s star-forming
regions from the inside out to better understand why
they are forming so many stars.
The team also has obtained data from
one of the twin Magellan Telescopes to help them
determine why the galaxy, which is 10 billion light
years away, looks so irregular.
“It’s not like we have something to
compare it to,” Sharon said. “We don’t know what
other galaxies at the same distance look like at
this level of detail.”
Source: redOrbit (http://s.tt/16TRE)
|
