Black holes are weird. Predicted as a result of Einstein’s general theory of relativity, they contain an outer region known as the event horizon – from which nothing, even light, can escape. In addition, they are predicted to have an infinitely compact point where our understanding of physics collapses, and nothing makes any sense anymore.
That’s before we even get into the black hole information paradox. If a black hole has mass (and they have a lot of it), then they should have a temperature according to the first law of thermodynamics, and according to the second law of thermodynamics, they should radiate heat. Stephen Hawking showed that black holes should emit radiation – now called Hawking radiation – formed at the boundary of a black hole.
“Hawking then pointed out a paradox: if a black hole is allowed to evaporate, some of the information it contains is lost forever,” French astrophysicist Jean-Pierre Luminet explained in a 2016 review. in the thermal radiation emitted by a black hole is affected; it does not recapitulate information about matter previously swallowed by the black hole. The irreversible loss of information violates one of the basic postulates of quantum mechanics. According to the Schrödinger equation, physical systems that change over time cannot create or destroy information, a property known as unitarity.
In short, we’re probably missing something. Physicists and mathematicians have tried to come up with ideas to solve these problems, and have come up with some pretty strange results. Some have even suggested that the universe could be holographic, with the universe we know and love actually being the result of interactions at the infinitely distant frontier. We told you black holes were weird.
And yet we have certainly observed objects that appear to have the properties of black holes, including (but far from limited to) the image of the black hole M87*. But what if they don’t exist at all?
One idea is that black holes are actually ‘gravastars’, a combination of gravity, vacuum and stars. First proposed in 2002 by Pawel O. Mazur and Emil Mottola, the idea is that at some point during the collapse of a large star, intense gravity transforms its matter into a new state similar to the Bose-Einstein condensate (BEC).
BEC occurs when atoms are cooled to such low energy states that they begin to behave like a single “super atom.” In gravastars, the team suggested that when the star collapses to the point of the event horizon, its matter is transformed into a new state, which exerts outward pressure and prevents the star from collapsing into a physics-defying singularity. In gravastars, this heavily distorted (but familiar) spacetime is surrounded by an ultra-thin, ultra-cold, ultra-dark, and virtually indestructible shell.
“Since this new form of matter is very durable, but somewhat flexible, like a bubble, anything that would get caught by the intense gravity and thrown into it would be obliterated and then absorbed into the shell of the Gravastar,” said Mottola in a statement. in response to the first article about gravastars.
One of the main appeals of gravastars is the elimination of cluttered event horizons and singularities. But while they are interesting as an idea, they must also explain what we observe, and we have certainly observed objects that look like black holes.
“This shadow is not caused by the trapping of light in the event horizon, but by a slightly different phenomenon called the ‘gravitational redshift’, which causes light to lose energy as it moves through an area with a strong gravitational field,” says João Luís Rosa . a professor of physics at the University of Gdańsk in Poland and author of a new study of gravastars told LiveScience. “Indeed, when the light emitted from areas close to these alternative objects reaches[es] Our telescopes would have lost most of its energy to the gravitational field, creating this shadow.”
As with black holes, things get messy when you add rotation, and there are (disputed) suggestions that gravastars would not be stable when they rotate. And they’re a little weird too (hey, this is the universe we’re talking about). There are suggestions that the interior of gravastars might contain a series of thicker shells known as nestars.
They’re not perfect, and there’s still a lot of work to be done to model how they work. It is also possible that both black holes and gravastars exist. A major problem is that it is difficult to distinguish between the two, although some models suggest that they should emit very different gravitational radiation, allowing us to know whether we are looking at gravastars or traditional black holes, and all the problems they face entail.
The new study by Rosa and colleagues is published in Physical Review D.