20-year dark matter mystery `unravelled`
Washington: Astronomers believe that they have found the answers to a 20-year debate over how dark matter is distributed in small galaxies.
Graduate student John Jardel and his advisor Karl Gebhardt found that the distribution, on average, follows a simple law of decreasing density from the galaxy`s center, although the exact distribution often varies from galaxy to galaxy.
Jardel`s work set out to study the question using both data from telescopes and newly developed computer modeling. The project started out "not assuming core or cusp theory is right," he says, "but just asking `what is it?.` These new models allowed us to take this approach."
Jardel used telescope observations of several of the satellite galaxies orbiting the Milky Way, including the Carina, Draco, Fornax, Sculptor , and Sextans dwarf galaxies.
The work involved running many supercomputer models for each galaxy to determine the distribution of dark matter within it, using the university`s Texas Advanced Computing Center (TACC).
He found that in some of the galaxies, the dark matter density decreased steadily from the center. In others, the density held constant. And some galaxies fell in between. However, when all the galaxies` distributions were analyzed together, the results showed that on average, the theorists were right.
Jardel said that when they look at individual galaxies, some of them look wildly different from expectations but when several galaxies are averaged together, these differences tend to cancel each other out.
This seems to suggest that the theory behind dark matter in galaxies is correct on the whole, but that `each galaxy develops slightly differently.`
The findings have been published in The Astrophysical Journal Letters.
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