Enlarge (credit: NASA, ESA, and M. Mutchler (STScI))
The Universe, according to cosmologists, is divided into three unequal portions. In the big bargain bin near the exit aisle you’ll find dark energy. Dark energy’s job is to push everything apart. There’s lots of it, and no one knows why. Then, next to to dark energy, on a display shelf, you’ll find a smaller amount of dark matter. Regular matter, the stuff you and I can see, is tucked off to the side: small and barely noticeable.
But the Universe isn’t a store’s display, and these individual parts can interact. Many of our models for dark matter predict a hierarchy of structures—halos of dark matter in and around galactic clusters and individual galaxies that hold them together. At large scales, we can detect these halos through gravitational lensing. Because there are observations to constrain them, all current theories of dark matter predict large halos correctly.
However, these same theories also predict smaller halos with sizes between 1,000 and a billion solar masses. In this mass range, we have no observations, and consequently, current theories disagree. These tiny halos are going to be hard to spot though: their gravitational effect—the only way we can see them—will be minimal. But, now a group of researchers may have figured out a new way to spot some of them.
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Source: Ars Technica – Dark matter halos may leave twinkling wake in galaxies