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For astronomers¹ who study the large-scale structure of the universe, dwarf² galaxies³ have proven quite vexing⁴. Because the leading model of cosmology has been unable to account for their relative lack of substance. Now scientists writing in the journal Nature show that the current model can actually generate dwarf galaxies just fine. You just need to look at the stars.

There are two types of matter in the universe: ordinary matter, including the material that makes up stars. And dark matter: that mysterious stuff we can’t see but that clearly affects ordinary matter. It’s the presence of cold dark matter that explains how the young universe went from being smooth to being lumpy, as ordinary matter coalesced⁵ first into stars and then into galaxies. The problem is dwarf galaxies are not as dense⁶ as the cold dark matter model says they should be.

Now an international team of astronomers says you can blame gusts⁷ of stellar wind. Because in the roiling⁸ cauldron of activity that governs galaxy⁹ formation, some stars go supernova. Those spectacular explosions literally¹⁰ blow matter away, and you’re left with a dwarf galaxy that’s a lot like most independent films: a bit light on stars.

—Karen Hopkin