Echoes in gravitational wave signals suggest that the event horizon of a black hole may be more complicated than scientists currently think.

Research from the University of Waterloo reports the first tentative detection of these echoes, caused by a microscopic quantum “fuzz” that surrounds newly formed black holes.

Gravitational waves are ripples in the fabric of space-time, caused by the collision of massive, compact objects in space, such as black holes or neutron stars.