for National Geographic News
Astronomers have found three galaxies in a never before seen perfect alignment—a discovery that may help scientists better understand the mysterious dark matter and dark energy believed to dominate the universe.
The three galaxies are like beads on a string, one directly behind the other, scientists announced yesterday at a meeting of the American Astronomical Society in Austin, Texas.
This makes the massive galaxy closest to Earth appear nestled in a pair of circular halos known as Einstein rings.
The phenomenon occurs because the gravity of the nearest galaxy distorts the light of the background galaxies as it travels toward Earth. The effect is called a gravitational lens.
When two galaxies are lined up perfectly, the distorted light forms a circle—a so-called Einstein ring. In this case, a third perfectly aligned galaxy forms a second, larger ring.
"Having three objects almost perfectly aligned along the line of sight is an extremely rare event," Tommaso Treu, an astrophysicist at the University of California, Santa Barbara, said at the press briefing.
"It's more unlikely than winning two consecutive bets in a single number of roulette."
Secrets of Nature
Not only is the optical alignment rare, but it also sheds light on some of the greatest mysteries of the cosmos, including dark matter and dark energy, Tommaso added.
"If you have two Einstein rings, you can start to measure a lot of things that you wouldn't be able to with just one ring," he said in a telephone interview Wednesday.
Dark matter, for instance, does not give off or emit light, so the substance can only indirectly be observed by the effects of its gravity. (Related: "Dark Matter Ring Detected by Hubble" [May 15, 2007].)
The double Einstein rings allow astronomers to calculate how dark matter is distributed in the galaxy closest to Earth by observing how the substance's gravity bends light from the more distant galaxies.
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