A mysterious cosmic event might have ever-so-slightly stretched and squeezed our planet last week. On Jan. 14, astronomers detected a split-second burst of gravitational waves, distortions in space-time … but researchers don’t know where this burst came from.

The gravitational wave signal, picked up by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo interferometer, lasted only 14 milliseconds, and astronomers haven’t yet been able to pinpoint the burst’s cause or determine whether it was just a blip in the detectors.

Gravitational waves can be caused by the collision of massive objects, such as two black holes or two neutron stars. Astronomers detected such gravitational waves from a neutron star collision in 2017 and from one in April of 2019, according to new findings that were presented at the meeting of the American Astronomical Society on Jan. 6.

Read more: space