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See a dark-matter magnet

NASA / ESA / ESO / CXC / Penn State
This Hubble-Chandra image highlights the X-ray halo surrounding the elliptical galaxy NGC 1132. Click
on the image for a larger version.

The Hubble Space Telescope has added a new view of the giant elliptical galaxy NGC 1132, filling out our picture of a huge depository of dark matter that may have coalesced from smaller galaxies – or somehow formed in isolation as a "lone wolf" in the cosmos.

Elliptical galaxies tend to look like unremarkable fuzzballs, but there's something special about this one: It has an impressive halo of X-ray-emitting gas - which shows up in shades of blue and purple in this image, a composite of Hubble's visible-light view and a false-color view from the Chandra X-Ray Observatory.

Based on how the X-ray halo is gravitationally bound to the galaxy, astronomers figure that there's enough dark matter within NGC 1132 for a whole cluster of galaxies.

Dark matter is a mysterious invisible substance that can be detected only by its gravitational effect. It may be made up of exotic subatomic particles or unseen objects. Whatever it is, dark matter appears to make up as much as 90 percent of the matter in the universe. That's a mystery exceeded in magnitude only by dark energy, an unknown factor that scientists say accounts for almost three times as much of the universe's combined matter-energy content. (Of course, they could be wrong.)

All that dark matter makes astronomers think that NGC 1132 grew up through the mergers of many smaller galaxies in an entire group, drawn in by the dark matter. That's why the galaxy is sometimes called a "fossil group." However, they can't rule out a scenario in which NGC 1132 was born as a full-fledged giant - perhaps under conditions that somehow suppressed the formation of lesser galaxies.

NGC 1132 is in the southern constellation Eridanus, 318 million light-years from Earth. The Hubble imagery was collected in 2005 and 2006 using the telescope's Advanced Camera for Surveys. Even though NGC 1132 itself is featureless, a high-resolution view offers gobs of galaxies to feast your eyes on. (Here's an even higher-resolution version.)

Check out the Space Telescope Science Institute's Hubblesite and the European Space Agency's Hubble Information Center to learn more about the dark-matter magnet - and click through our space gallery for additional highlights from Hubble.