A new study suggests that black holes may not be the featureless, structureless entities Einstein imagined. general theory of relativity predicted that. Instead, the cosmic monster may be a strange quantum object known as a “frozen star.”
Although it has some similarities to black holeThe hypothetical celestial objects differ in crucial ways that could potentially resolve the famous Hawking radiation paradox (named after the late physicist Stephen Hawking, who proposed the phenomenon). The paradox arises because the theoretical radiation emitted by a black hole’s event horizon does not appear to carry information about the matter that formed the black hole, which contradicts a fundamental principle quantum mechanics states that information cannot be destroyed.
Additionally, unlike conventional black holes, frozen stars are not expected to have singularities — points of infinite density at their centers — which resolves another contradiction between the classical picture of black holes and the general rule in physics that infinity is impossible in natureWhen infinity appears in a theory, it usually indicates a limitation of the theory.
“Frozen stars are a type of black hole mimic: ultracompact astrophysical objects that are free of singularities, have no horizons, yet can mimic all the observable properties of black holes,” Ramy Brustein“If they really exist, they would indicate the need to significantly and fundamentally modify Einstein’s general theory of relativity,” a physics professor at Ben-Gurion University in Israel, told Live Science in an email.
Brustein is the lead author of a study explaining the frozen star theory, published in July in the journal Physical Review D.
Resolving the paradox
The classical model of a black hole, first described by Karl Schwarzschild in 1916, describes a black hole as having two key features: a singularity where all the mass is concentrated and an event horizon, a boundary beyond which nothing, not even light, can escape.
However, this model faced serious problems when quantum mechanics was introduced. In the 1970s, Stephen Hawking discovered that quantum effects near the event horizon should lead to the creation of particles from the vacuum, a process known as Hawking radiation. This radiation would cause the black hole to gradually lose mass and finally evaporates completely.
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This paradox arises because this radiation does not seem to carry any information about the matter that originally formed the black hole. If the black hole evaporates completely, this information seems to be lost forever, violating the principles of quantum mechanics, which state that information must be conserved. This contradiction is known as the information loss paradox, and it has become one of the most significant challenges in theoretical physics.
In their new study, Brustein and co-authors AJM Medved from Rhodes University and Tamar Simhon from Ben-Gurion University conducted a detailed theoretical analysis of the frozen star model, and found that it resolves the paradoxes of traditional models by lacking a horizon and a singularity.
The authors found that if black holes are actually extremely dense objects composed of ultra-rigid matter whose properties are inspired by string theory, a prime candidate for the theory quantum gravitythey do not collapse into very dense points, and have a size slightly larger than a conventional event horizon, thus preventing the latter from forming.
“We have shown how frozen stars behave as (almost) perfect absorbers despite having no horizon and acting as sources gravitational waves” Brustein said, noting that these objects can absorb almost anything that falls on them, like a black hole. “In addition, they have the same external geometry as conventional black hole models and reproduce their conventional thermodynamic properties.”
Testing the frozen star hypothesis
While the frozen star model presents a potential solution to the paradoxes associated with traditional black holes, scientists still need to test it experimentally.
But unlike conventional black holes, frozen stars are thought to have internal structure, albeit with strange properties dictated by quantum gravity. This paves the way for distinguishing the two observationally. Evidence for this can be seen in gravitational waves — ripples in the fabric of space-time — produced during black hole merger.
“This is when the differences will be most pronounced,” Brustein explains.
The team still needs to figure out what exactly the internal structure of the frozen star would be like, and how it would differ from other extreme cosmic objects like neutron stars, but that’s within reach, Brustein said. From there, they can analyze data from existing and future gravitational-wave observatories, since the gravitational waves emitted during a merger are incredibly powerful and could carry information about the structure of these ultracompact objects.
“The discovery of one of the predictions of the frozen star model would have revolutionary implications,” Brustein said.
