There are black holes in the universe. The equations of general relativity that are used to understand them break down when studying black holes.

A new paper shows how astronomy could one day be able to see inside black holes by using waves from the universe.

Gravitational microscopes

Black holes are objects that prevent light from escaping due to their heavy gravity. If you pass beyond the event horizon, you will never make it out of a black hole. The centers of black holes are known as singularities.

The presence of singularities means that the equations themselves are breaking down. General relativity isn't complete. There needs to be a more fundamental theory that explains what's happening in the center of a black hole.

There are several candidates for a complete quantum theory of gravity. The string theory claims that all particles in the universe are made of tiny vibrating strings. The loop quantum gravity states that space-time is made of tiny, indivisible chunks.

The center of a black hole can be replaced with something else with either approach. The event horizon is usually eliminated when you replace the singular. The event horizon is caused by the singularity. You're always able to escape the vicinity of a black hole if you run fast enough.

The event horizon is replaced by intertwined networks of knots of spacetime in some variations of string theory. The singularity becomes very dense in loop quantum gravity. The black hole is replaced by a thin shell of matter or by clumps of speculative particles.

Black hole mystery

It's difficult to test these models because they are close to the nearest known black holes. Black holes sometimes give us important information. The Laser Interferometer Gravitational-Wave Observatory (LIGO) and the VIRGO experiments can detect ripples in space-time that can be seen on Earth.

All of the observations of black hole mergers agree with the predictions of general relativity. A paper published in the preprint journal arXiv suggests that in the future that may change.

According to the paper, the key is not the waves that were emitted during the merger, but the waves that came after. The merged mass is vibrating with an intense amount of energy when it becomes a single object. The phase has a signature.

Researchers may one day be able to tell which black hole theories hold up and which don't. Differences in the black hole's interior structure are predicted by the black hole models. Different types of waves come out of black holes.

The ringdown signature is predicted to be changed by the next generation of gravitational wave detectors. They will change our conception of black holes if they do.

The original article was published on Live Science.