Stephen Hawking's black hole paradox may finally be solved

A new study suggests that black holes may not be featureless entities as predicted by Einstein’s general theory of relativity. Instead, these “cosmic monsters” might be strange quantum objects known as “frozen stars.” But what exactly is the black hole radiation paradox?

Although frozen stars would share some similarities with black holes, they differ in essential ways that could potentially resolve Stephen Hawking’s black hole radiation paradox. The paradox arises because the radiation theoretically emitted from a black hole’s event horizon seems to carry no information about the matter that formed the black hole, violating the core principle of quantum mechanics, which states that information cannot be destroyed.

Additionally, unlike conventional black holes, frozen stars are not expected to contain a singularity (a point of infinite density at their center), addressing another conflict between classical black hole models and the general rule in physics that infinities cannot exist in nature. The presence of infinities in a theory often signals the limitations of that theory, as explained by Live Science.

The black hole radiation paradox—closer than ever to being solved

“Frozen stars are a type of black hole mimic: ultra-compact astrophysical objects without singularities or event horizons, but capable of imitating all observable properties of black holes. If these objects exist, they would imply a fundamental need to modify Einstein’s general relativity,” said Ramy Brustein, a physics professor at Ben-Gurion University in Israel.

Brustein is the lead author of a study that details the frozen star theory, published in Physical Review D.

The classical black hole model, first described by Karl Schwarzschild in 1916, defines black holes as having two key features: a singularity where all mass is concentrated, and an event horizon, the boundary beyond which nothing, not even light, can escape.

Why general relativity might be wrong about black holes

However, this model faces serious challenges when quantum mechanics is introduced. In the 1970s, Stephen Hawking discovered that quantum effects near a black hole’s event horizon should lead to the creation of particles from the vacuum of space—a process now known as Hawking radiation. This radiation would cause the black hole to gradually lose mass and eventually evaporate.

The black hole radiation paradox arises because Hawking radiation does not seem to carry information about the matter that initially formed the black hole. If the black hole completely evaporates, this information appears to be lost forever, which contradicts the fundamental principle of quantum mechanics that information must be preserved. This contradiction is known as the information loss paradox, one of the greatest challenges in theoretical physics.

What are frozen stars?

In their new study, Brustein and his co-authors, A.J.M. Medved from Rhodes University in South Africa, and Tamar Simhon from Ben-Gurion University, conducted a detailed theoretical analysis of the frozen star model. They discovered that frozen stars resolve the paradoxes of traditional black hole models because they do not involve an event horizon or a singularity.

The researchers found that if black holes are actually ultra-compact objects made of extremely rigid matter—whose properties are inspired by string theory (a leading candidate for quantum gravity theory)—these objects do not collapse into points of infinite density. Instead, they maintain a size slightly larger than the conventional event horizon, preventing its formation.

“We have shown how frozen stars behave as almost perfect absorbers, even without an event horizon, and act as a source of gravitational waves,” said Brustein, explaining that these objects can absorb nearly everything that falls into them, much like black holes. “Moreover, they generate the same external geometry as traditional black holes and replicate their thermodynamic properties.”

Could frozen stars be the answer to Hawking’s black hole radiation paradox?

The frozen star model offers a potential solution to the paradoxes linked to traditional black holes, but scientists will need to test it through observation.

Unlike conventional black holes, frozen stars are expected to have an internal structure, albeit a bizarre one governed by quantum gravity. This opens the possibility for observational distinctions between the two models. Evidence could be found in the gravitational waves—ripples in space-time—generated during black hole mergers. “This is where the differences would be most apparent,” explained Brustein.

The team is still working to understand the internal structure of frozen stars and how they differ from other extreme cosmic objects like neutron stars. However, this is a realistic goal, Brustein noted. From there, they could analyze data from existing and future gravitational wave observatories, as the waves emitted during mergers are incredibly powerful and could reveal the structure of these ultra-compact objects.

“Any discovery that supports the frozen star model would have a revolutionary impact,” concluded Brustein.

Fact check: Key information from the article

The black hole radiation paradox was introduced by Stephen Hawking in the 1970s.
The paradox stems from the idea that Hawking radiation does not contain information about the matter that formed the black hole.
Frozen stars could offer a solution, as they lack both a singularity and an event horizon.
The frozen star model suggests that these objects absorb matter like black holes but without violating the laws of quantum mechanics.
Testing the model through gravitational waves from black hole mergers could confirm or refute the theory.