In early 2016, scientists at LIGO detected gravitational waves, 100 years after Albert Einstein had theorised them.
It had been thought that the gravitational waves that were detected by scientists had originated from two black holes colliding, but a team of researchers have different ideas.
Experts from the University of Lisbon say that the gravitational waves could have come about as a result of a wormhole or a gravastar – two entities which are thought to have their insides made up of dark energy.
A gravastar is an alternative to the black hole theory which suggests that black holes are not “holes” where light cannot escape, but rather spherical voids in space.
A wormhole is a connection between one point in space and a far away region, essentially a shortcut.
Neither theories have been fully proven, however, they could go towards explaining gravitational waves.