The Universe Used as a Lens
CHICAGO, Feb. 25, 2009 – Scientists are harnessing the cosmos as a scientific “instrument” in their quest to determine the makeup of the universe.
The University of Chicago’s Evalyn Gates calls the instrument “Einstein’s telescope.” The instrument is actually the phenomenon of gravitational lensing, which acts as a sort of natural telescope. Gates’ new book, “Einstein's Telescope: The Hunt for Dark Matter and Dark Energy in the Universe,” explains how it works. (See a video of Gates explaining gravitational lensing here.)
Galaxies can warp space and time, distorting our view of distant objects, much the way this plexiglass lens distorts the appearance of University of Chicago astrophysicist Evalyn Gates. Astrophysicists use this effect, called gravitational lensing, in their studies of the cosmos. Gates explains how in her new book, “Einstein's Telescope: The Hunt for Dark Matter and Dark Energy in the Universe.” (Photo: Dan Dry)
Although based on Albert Einstein’s general theory of relativity, the effect is easily demonstrated. Look at a light through the bottom of a wine glass, Gates recommends, and see the resulting light distortion.
“Einstein’s telescope is using the universe itself as a lens through which we can seek out galaxies that would otherwise be too faint to be seen,” said Gates, assistant director of the university’s Kavli Institute for Cosmological Physics.
Long ago, Einstein recognized the potential existence of gravitational lensing, a consequence of his theory of general relativity. According to general relativity, celestial objects create dimples in space-time that bend the light traveling from behind.
Einstein realized that the gravitational influence of a foreground star could theoretically bend the light of another star sitting almost directly far beyond it, producing two images of the background star.
“Gravitational lensing magnifies things as well as making multiple images and distorting the shape of images, so you can actually use it as a magnifying glass,” Gates said.
But, assuming that the effect would be too weak to detect, Einstein immediately dismissed its significance.“What he didn’t anticipate, among other things, were the incredible leaps forward in telescope technology,” Gates said.
Astronomers now use gravitational lensing to look for dark matter and the imprint of dark energy, two of the greatest modern scientific mysteries.
Dark energy, which acts in opposition to gravity, is the dominant force in the universe.
“We can’t see dark energy directly by any means, but we’re looking for how it has sculpted the matter distribution of the universe over the past few billion years, since it’s been the dominant factor, and also how it has affected the rate at which the universe is expanding,” Gates said.
The Hubble Space Telescope captured this image of galaxy cluster Abell 1689. This view shows the cluster bending light from galaxies that lie behind it to produce multiple, curved images of the distant galaxies. (Image: NASA, N. Benitez [JHU], T. Broadhurst [Hebrew University], H. Ford [JHU], M. Clampin [STScI], G. Hartig [STScI], G. Illingworth [UCO/Lick Observatory], ACS Science Team and ESA STScI-PRC03-01a)
And gravitational lensing is essentially the only method astronomers have for tracing out the web of dark matter that pervades the universe, and for determining how dark energy has impacted the evolution of this web. “It’s really hot scientifically,” she said.
As with dark energy, dark matter also is invisible. It accounts for most of the matter in the universe, but exactly what it is remains unknown. Scientists know only that dark matter differs significantly from normal matter (which is essentially composed of protons and neutrons) that dominates everyday life.
“What we’re made of is just about five percent of everything that’s in the universe,” Gates said.
In the 1990s, scientists wondered whether a significant quantity of dark matter in the halo consisted of MACHOs (Massive Astrophysical Compact Halo Objects) – faint objects such as dim stars, Jupiter-size planets or stellar-mass black holes that are all composed of normal matter but hard to see.
Gates and her collaborators were among the researchers who used gravitational lensing to search for MACHOs within the halo of the Milky Way galaxy.
“We have seen MACHOs, but what we found is that they make up, at most, a small fraction of the galactic halo,” Gates said.
Scientists also use galaxy clusters as gravitational lenses to probe 13 billion years back into the history of the universe. “They’re seeing some of the very first galaxies,” she said. Gravitational lensing offers astrophysicists a tool comparable to magnetic resonance imaging and computing tomography, which have provided health professionals with unprecedented new views of the human body.
“Gravitational lensing is going to allow us to image the universe in ways that wouldn’t have been possible even 50 years ago,” she said.
During the 20th century, quantum mechanics and general relativity radically altered scientists’ view of the universe, Gates said. Investigations of dark matter and dark energy may do likewise.
“It may lead us to another revolution in our understanding of the most fundamental aspects of the universe, time, matter, and energy,” she said.
For more information, visit: http://cfcp.uchicago.edu
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