Sept. 18, 2007 — The 70-year effort to unravel the mysteries of dark matter just got a big boost from some very puny galaxies.
In the past few years a score of dwarf galaxies have been discovered hanging about the fringes of the Milky Way. Now new measurements of the few stars in these dwarfs reveal them to be dark matter distilleries, with upwards of 1,000 times more dark matter than normal matter.
As a result, the dwarfs seem like a likely place to learn more about the elusive stuff.
Dark matter has long stumped scientists since it is something that has gravity but appears to not interact in any other way with the normal matter that makes up people, the planets and the stars.
The reason astronomers suspect dark matter exists is that measurements of the quantities of visible matter in galaxies, and stars within galaxies, persistently come up short on matter to explain how they were moving.
It was as if they had invisible dance partners. Exactly what the dance partner — this dark matter — is, however, remains a nagging enigma.
The current most favored theory is that it is some sort of particle that interacts only extremely rarely with normal matter in any other way than tugging its gravity.
Physicists hope to settle the question in the next few years by possibly creating dark matter particles in the world’s largest particle accelerator, the Large Hadron Collider, set to begin working next year at CERN, a particle physics laboratory in Geneva.
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Dwarf Discoveries
In the meantime, space is still the best place to detect the effects of dark matter and narrow down the constraints on what sort of particles dark matter might be. The newfound dwarf companions to the Milky Way are now presenting a rare opportunity to learn details about how dark matter behaves on a relatively small scale very close to home.
"There are many ways to look at larger-scale distribution of dark matter," said dwarf galaxy investigator Beth Willman, a fellow at the Harvard-Smithsonian Center for Astrophysics.
Already there are lots of models looking at the overall distribution of dark matter in the universe, which help to make sense of the structure of the universe in the largest scale.
"But as you go to smaller and smaller scales," she said, "the predictions of those models can be quite different."
