Public Release: 

Surprise: Satellite galaxies of Centaurus A are on a coordinated dance

American Association for the Advancement of Science

The satellite dwarf galaxies orbiting around the much larger galaxy Centaurus A are rotating in synchrony around their host, to researchers' surprise. (Researchers expected them to orbit at random). The results contradict simulations based on standard cosmology, which predict that fewer than 1% of satellite systems should exhibit this synchronous behavior. Because our own Milky Way and the neighboring Andromeda Galaxy also have similar arrangements of coherently orbiting satellite galaxies, this finding suggests that standard cosmological simulations may be wrong. Current theories of galaxy formation, based on standard cosmological ingredients such as dark matter, predict that small dwarf satellite galaxies should orbit in random positions and directions around their closest large galaxy. Oliver Müller et al. analyzed the satellite galaxies around Centaurus A, a nearby large elliptical galaxy. They found that the satellite galaxies are not only arranged in a single plane, but the plane also rotates coherently: satellite galaxies on one side of Centaurus A are approaching, while those on the other side are receding. Of the 16 satellite galaxies for which scientists have data, 14 followed this organized movement - and yet the probability of such a scenario is a mere 0.5% based on simulations, the authors say. These results hint that widely accepted models of cosmology and/or galaxy formation are lacking, or at least misconstruing crucial components. In a related Perspective, Michael Boylan-Kolchin writes, "The results may lead to either a better understanding of galaxy formation within the [cold dark matter] model or a push to overthrow its underlying assumptions."

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