Black holes are strange. Predicted as a result of Einstein’s general theory of relativity, they contain an outer region known as the event horizon – from which nothing, not even light, can escape. In addition, they are predicted to have an infinitely dense point where our understanding of physics breaks down and nothing makes sense.
That’s before we get into the black hole information paradox. If a black hole has mass (and many do), then they must have a temperature according to the first law of thermodynamics, and according to the second law of thermodynamics, they must radiate heat. Stephen Hawking showed that black holes must emit radiation – now called Hawking radiation – formed at the boundary of a black hole.
“Hawking then pointed out a paradox. If a black hole can evaporate, some of the information it contains is lost forever,” explains French astrophysicist Jean-Pierre Luminet in a 2016 review. “The information contained in the thermal radiation of emitted by a black hole is degraded; it does not summarize the information previously swallowed by the black hole. The irreversible loss of information contradicts one of the basic postulates of quantum mechanics over time cannot create or destroy information, a property known as unitarity.”
In short, maybe we’re missing something. Physicists and mathematicians have tried to come up with ideas that eliminate these problems and ended up with some pretty strange results. Some have even suggested that the universe may be holographic, with the universe we know and love really being the result of interactions at infinitely distant boundaries. We told you black holes were weird.
And yet, we have definitely observed objects that appear to have the properties of black holes, including (but not 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 portmanteau 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 massive 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 a low energy state that they begin to act as a single “super atom”. In gravastar, the team suggested that as the star collapses to the point of the event horizon, its matter transforms into a new state, which exerts outward pressure and prevents the star from collapsing into a physics-defying singularity. In gravastar, this highly warped (but familiar) space-time is surrounded by an ultra-thin, ultra-cold, ultra-dark and virtually indestructible shell.
“Since this new form of matter is very stable but somewhat flexible, like a bubble, anything that was trapped by its intense gravity and crashed into it would be swept away and then assimilated into the Gravastar shell “, Mottola said in a statement. following the first letter on gravastar.
One of the main appeals of gravastars is the removal of messy event horizons and features. But while interesting as ideas, they also have to explain what we observe, and we certainly have observed objects that look like black holes.
“This shadow is not caused by the capture of light at the event horizon, but by a slightly different phenomenon called ‘gravitational redshift,’ which causes light to lose energy as it moves through a region with a strong gravitational field,” João Luís Rosa. , a professor of physics at the University of Gdańsk in Poland and author of a new gravastar study, told Live Science. “Indeed, when light emitted from regions near these alternative objects arrives[es] our telescopes, most of its energy would have been lost to the gravitational field, causing this shadow to appear.”
As with black holes, things get messy when you add spin, and there are suggestions (contradicted) that gravastars would not be stable as they spin. And they’re a little weird too (hey, this is the universe we’re talking about). There are suggestions that the interior of gravastars may contain a series of thicker shells, known as nestars.
They are not perfect and there is a lot of work to be done in modeling how they work. It is also possible that both black holes and gravastars exist. A big problem is that it’s hard to tell the difference between the two, although some models suggest that they should emit very different gravitational radiation, allowing us to know whether we’re looking at gravastars or traditional black holes, and all the pain of the head they bring.
The new study by Rosa and colleagues is published in Physical Review D.