Weird dark clusters appear near a large galaxy, NASA creates a Jupiter moon in a can, Saturn's rings go razor-thin and more in our selection of the week's best space-related images.
Something strange is afoot in the elliptical galaxy Centaurus A. In a recent survey of its star clusters, astronomers found that some are far more massive than they should be based on the matter we can see. The result suggests that a new and mysterious class of dark globular clusters may lurk around galaxies across the cosmos.
Globular clusters are loosely bound balls of old stars that orbit most galaxies. Astronomers can weigh them from afar and get a rough count of their stars based on brightness. Until now, such clusters usually had just the right amount of stars to account for their masses. But using ESO’s Very Large Telescope in Chile, astronomers have now found that most of the clusters in a sampling around Centaurus A have way more mass than their brightness suggests. These clusters may be packed with quiescent black holes, the scientists say, or they may contain large amounts of the mysterious substance known as dark matter. Either way, the finding challenges current theories of globular cluster formation.