WHAT LIES BEYOND A BLACK HOLE??
Saturday, August 13th, 2022
The singularity at the center of a black hole is the ultimate no man’s land: a place where matter is compressed down to an infinitely tiny point, and all conceptions of time and space completely break down. And it doesn’t really exist. Something has to replace the singularity, but we’re not exactly sure what.
Let’s explore some possibilities.
It could be that deep inside a black hole, matter doesn’t get squished down to an infinitely tiny point. Instead, there could be a smallest possible configuration of matter, the tiniest possible pocket of volume.
This is called a Planck star, and it’s a theoretical possibility envisioned by loop quantum gravity, which is itself a highly hypothetical proposal for creating a quantum version of gravity. In the world of loop quantum gravity, space and time are quantized — the universe around us is composed of tiny discrete chunks, but at such an incredibly tiny scale that our movements appear smooth and continuous.
This theoretical chunkiness of space-time provides two benefits. One, it takes the dream of quantum mechanics to its ultimate conclusion, explaining gravity in a natural way. And two, it makes it impossible for singularities to form inside black holes.
As matter squishes down under the immense gravitational weight of a collapsing star, it meets resistance. The discreteness of space-time prevents matter from reaching anything smaller than the Planck length (around 1.68 times 10^-35 meters).
All the material that has ever fallen into the black hole gets compressed into a ball not much bigger than this. Perfectly microscopic, but definitely not infinitely tiny.
This resistance to continued compression eventually forces the material to un-collapse (i.e., explode), making black holes only temporary objects. But because of the extreme time dilation effects around black holes, from our perspective in the outside universe it takes billions, even trillions, of years before they go boom. So we’re all set for now.
Another attempt to eradicate the singularity — one that doesn’t rely on untested theories of quantum gravity — is known as the gravastar. It’s such a theoretical concept that my spell checker didn’t even recognize the word.
The difference between a black hole and a gravastar is that, instead of a singularity, the gravastar is filled with dark energy. Dark energy is a substance that permeates space-time, causing it to expand outward. It sounds like sci-fi, but it’s real: dark energy is currently in operation in the larger cosmos, causing our entire universe to accelerate in its expansion.
As matter falls onto a gravastar, it isn’t able to actually penetrate the event horizon (due to all that dark energy on the inside) and therefore just hangs out on the surface. But outside that surface, gravastars look and act like normal black holes. (A black hole’s event horizon is its point of no return — the boundary beyond which nothing, not even light, can escape.)
However, recent observations of merging black holes with gravitational wave detectors have potentially ruled out the existence of gravastars, because merging gravastars will give a different signal than merging black holes, and outfits like LIGO (the Laser Interferometer Gravitational-Wave Observatory) and Virgo are getting more and more examples by the day. While gravastars aren’t exactly a no-go in our universe, they are definitely on thin ice.
Originally published on www.space.com
(Wednesday, August 17th, 2022)
