Scientists are using funhouse images of faraway galaxies to learn how dark matter shaped the cosmos we see today. This picture from the Hubble Space Telescope, with the monster galaxy cluster MACS J1206.2-0847 (or MACS 1206 for short) at the center, illustrates how gravitational lenses can focus on phenomena that would otherwise go unseen.
Notice how a lot of the galaxies surrounding the central smudge of light have been distorted into thin arcs of light. That's due to the light-bending effect of the massive MACS 1206, as dictated by Einstein's general theory of relativity. Astronomers can do a careful analysis of those distortion effects to figure out just how massive the galaxy cluster is, and even where the mass is most concentrated.
Scientists have known for a long time that such galaxy clusters are much more massive than they thought they'd be, based on how much light they're giving out. The motions of galaxies suggest that visible matter makes up 15 percent or less of the universe's total mass. The rest of the stuff is the dark matter. It's not yet clear exactly what dark matter is, but scientists suspect it consists of exotic particles that don't interact much with the "ordinary" matter we all know and love.
MACS 1206, which lies 4.5 billion light-years from Earth, is one of 25 galaxy clusters that have been targeted by an effort known as the Cluster Lensing and Supernova Survey Using Hubble, or CLASH. So far, the effort has completed its observations for six of the clusters. By analyzing variations in the gravitational effects, the CLASH team hopes to map out how dark matter's effect has shaped galaxy clusters over time.
"These maps are being used to test previous, but surprising, results that suggest that dark matter is more densely packed inside clusters than some models predict," Hubble's handlers say in an image advisory issued today. "This might mean that galaxy cluster assembly began earlier than commonly thought."
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