NGC 247, holed (Image: ESO)

A GIANT clump of dark matter may have smashed into a nearby galaxy and punched a hole in its starry disc.

The victim is NGC 247, a small spiral galaxy 11 million light years away, which sports a void that spans a sixth of its diameter. It does harbour some stars, but a new study of Hubble images found they are on average about a billion years older than those surrounding the void.

Stars form when swirling gas coalesces, so the void’s existence suggests the region was robbed of its gas. “Clearly, something caused this,” says Ata Sarajedini at the University of Florida in Gainesville. “But there’s no smoking gun.” No visible galaxy lurks nearby that could be the culprit.


Instead, he and his colleagues invoke an invisible galaxy made of dark matter and a touch of gas (Monthly Notices of the Royal Astronomical Society, doi.org/t7f). When this “dark subhalo” hit NGC 247, its gas pushed aside the galaxy’s gas, compressing it into a ring of new stars.

A ring of bright stars surrounding the solar system, called Gould’s belt, could be evidence that a similar dark subhalo smacked into the Milky Way 30 million years ago.

This article appeared in print under the headline “Dark matter in hit-and-run smash”