Astronomers have discovered a small galaxy that is invisible to telescopes and may be completely composed of dark matter, which reflects no light. The newfound galaxy is incredibly distant and extremely small. It orbits as a satellite of a larger galaxy. Though telescopes can’t spot the dwarf galaxy, scientists detected its presence through the tiny distortions its gravity causes to light that passes it by. The new dwarf galaxy is about 7 billion light-years away. It weighs about 190 million times the mass of the sun. According to study co-author Matthew Auger of the University of California, Santa Barbara this is the lowest mass galaxy that they have seen at this distance by far. Because it is so far and hard to see, astronomers can’t be sure if the newly
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discovered galaxy really is made almost exclusively of dark matter, or if it just contains stars that are too dim to be visible at this distance. However, theoretical models aren’t clear on this issue, and astronomers would like to know more about when light matter galaxies form, and when dark matter clumps remain starless.