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An international team of astronomers, led by Pavel Mancera Piña (University of Groningen and ASTRON), has discovered six ultra-faint dwarf galaxies that contain hardly any dark matter. Thit is pretty unique as most ultra-faint dwarf galaxies are expected to be held together almost entirely by large amounts of dark matter. The researchers will soon publish their findings in The Astrophysical Journal Letters.
The astronomers used the Dutch Westerbork Synthesis Radio Telescope and the American Very Large Array for their research. They looked at six faint dwarf galaxies at 240 million light-years to 320 million light-years away. These types of galaxies have, as of yet, not been studied in detail because they provide little light.
The name dwarf galaxy in this group refers to the faintness of these galaxies and not to their size. They are just as big as our own Milky Way but contain fewer stars. The prevailing idea is therefore that such large dwarf systems can only exist if they are held together by dark matter.
The researchers were surprised to find that the faint dwarf galaxies and their environment did not seem to contain any dark matter at all. According to current theories, these six systems should not exist.
The researchers postulated a few explanations in their scientific publication for the lack of dark matter, but being honest, they say, they don't have a good explanation for it as of yet.
Earlier, another research group had also discovered two galaxies similar that also contained almost no dark matter. However, more details are now known about the six newly observed systems.
Sources and further reading: Astron Press Release - Off the baryonic Tully-Fisher relation: a population of baryon-dominated ultra-diffuse galaxies
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