Black holes echoing through spacetime could be telling us they aren’t what we think they are

Nothing — not even light — can escape a black hole, right? Black holes might not be the fathomless cosmic graves we think they are. Most scientists believe that once matter falls past the event horizon (basically the point of no return), intense gravity means that matter is a goner. Emphasis on most. Now physicist Niayesh Ashfordi of the University of Waterloo is challenging that belief based on the theory of gravitational wave “echoes” in spacetime that could mean not everything that dares to pass the event horizon will vanish forever.

Enter quantum black holes.

If matter echoing from an interaction with a black hole can be proven, it will shake physics like nothing else. Such echoes disrupt the curvature of spacetime that has been created over innumerable years by everything from astral explosions to planets smashing into each other. Ashfordi recently published a study in The Journal of Cosmology and Astroparticle Physics that suggests these gravitational wave echoes might have already been detected in a particular black hole, caused by an epic neutron star crash spinning at breakneck speed.

“If confirmed, this finding will have significant consequences for both physics of quantum black holes and astrophysics of binary neutron star mergers,” he and co-author Jahed Abadi said of the merger, GW170817, adding that it is “the first tentative detection of post-merger gravitational wave "echoes" from a highly spinning "black hole" remnant.”

But first, understanding gravitational wave echoes means you have to understand Hawking radiation.

Stephen Hawking’s black hole information paradox makes a shocking suggestion. Quantum black holes, or black holes that account for the extreme weirdness of quantum mechanics, might actually vomit matter it swallowed back out into the cosmos. The thing is, whatever escapes would have no information left about anything that happened before it fell victim to the gaping maw of that black hole. No matter. Quantum particles sneaking out of black holes still defy what we think we know about these star corpses. This theoretical phenomenon, in which particles radiate from a black hole until nothing remains, is Hawking radiation.

It sounds like it makes total sense until you realize it breaks the laws of the universe. Nothing, not even a black hole, is supposed to permanently delete information. So how could gravitational wave echoes even get out? Back to that neutron star merger. Gravitational waves are already known to come out of collisions that violent, and not only do they ripple out into space, but also bounce back. Never mind that physics would normally say this bouncing back of something that already overstepped the event horizon is impossible.

Ashfordi and Abedi said “tentative evidence for [gravitational wave echoes] has been found in binary black hole merger events” and that they discovered “a tentative detection of echoes”.

The scientists believe that a gravitational wave can get head-butted by quantum particles flying out of there, which makes that wave bounce back as an echo of the ripple that started all this chaos. Bouncing outward, this wave bumps into that luminous halo you probably saw in the first black hole image ever, also known as the photon ring. Echoes end up trapped between the quantum black hole and the photon ring. Some of them are believed to eventually break free, which is why traces of them may have already been observed. Upcoming telescopes like the Laser Interferometer Space Antenna (LISA) may be able to pick up these runaway echoes in the future.

While much still needs to be demystified, one thing that can be said for sure is that it’s definitely not aliens.

(via Motherboard/Journal of Cosmology and Astroparticle Physics)