The scientific collaborations LIGO and Virgo have detected gravitational waves from the fusion of two black holes, and a team of European physicists have investigated what would happen they were not produced by black holes but wormholes.
Questioning whether ripples of space-time had not been produced by black holes but by other exotic objects, a team of European physicists offer an alternative: wormholes, which can be traversed to appear in another universe.
Scientists have deduced the existence of black holes from several experiments, theoretical models and indirect observations, such as the recent detection, by the LIGO and Virgo observatories, of gravitational waves, which are supposed to originate from the collision of two of these blackholes.
However, black holes present a problem known as an event horizon, from which matter, radiation or anything that enters can no longer escape. This conflicts with quantum mechanics, whose postulates ensure that information is always preserved and not lost.
Dealing with this conflict
One theoretical way to deal with this conflict is to explore the possibility that the black holes we observe in nature are no such thing, but rather some kind of exotic compact objects (ECOs), such as wormholes, with one particularity: they do not have an event horizon, which leaves its mark on the gravitational waves recorded by LIGO and Virgo.
Spanish researchers Pablo Bueno and Pablo A. Cano from KU Leuven University (Belgium) said: “The final part of the gravitational signal detected by these two detectors – what is known as ringdown– corresponds to the last stage of the collision of two black holes, and has the property of completely extinguishing after a short period of time due to the presence of the event horizon.
“However, if there were no horizon, those oscillations would not disappear completely; instead, after a certain time, they would produce a series of ‘echoes’, similar to what happens with the sound in a well. Interestingly, if instead of black holes we had an ECO, the ringdown could be similar, so we need to determine the presence or absence of the echoes to distinguish the two types of objects.”
The research team has presented a model that predicts how gravitational waves caused by the collision of two specific ECOs would be detected: rotating wormholes.
So far, the gravitational wave signals observed are completely extinguished after a few moments because of the presence of the event horizon. Yet if this did not exist, these oscillations would not disappear altogether; rather, after some time, there would be echoes in the signal, which may have gone unnoticed until now due to a lack of models or theoretical references with which to compare.
Bueno concludes: “The confirmation of echoes in the LIGO or Virgo signals would be a practically irrefutable proof that astrophysical black holes don’t exist.”