Alternative models of black holes suggest that quantum effects can remove the need for peculiarities

Since the general relativity indicated the existence of black holes, the scientific community has been cautious for one special characteristics: peculiarities in the center – a hidden point behind the horizon of an event by which the laws of physics governing the rest of the universe appear to completely break down. For a while, scientists have been working on alternative models that are free of peculiarities.

New article published in Journal of Cosmology and Astroparticle PhysicsThe result of the work conducted at the Institute for Fundamental Physics of the Universe (IFPU) in Trieste, reviews the latest art on this field. He describes two alternative models, offers statement tests and examines how this research line can also contribute to the development of quantum gravity theory.

“Hic Sunt Leones”, notes Stefano Liberati, one of the authors of the article and IFPU director. This expression refers to the hypothetical peculiarity expected in the center of standard black holes – described by the solutions of Einstein’s field equations. To understand what this implies, a brief historical summary is useful.

In 1915, Einstein published his breakthrough work on general relativity. Just a 12 months later, German physicist Karl Schwarzschild found an intensive solution to those equations, which suggested the existence of extreme objects currently often called black holes. These are objects with such concentrated mass that nothing – even light – doesn’t escape from their gravitational pulling, hence the term “black”.

From the very starting, nonetheless, problematic features appeared and caused many years of the debate. In the sixties, it became clear that space -time curvature was becoming really infinite in the center of the Black Hole: a peculiarity by which the laws of physics – or it seems so – cuts.

If this peculiarity were true, not only a mathematical artifact, it might mean that general relativity is distributed in extreme conditions. For most scientific community, calling the term “singularity” has change into a sort of white flag: it signals that we just do not know what is going on on this region.

Despite the ongoing debate on peculiarities, scientific evidence of the existence of black holes has been continually growing since the seventies, culminating with the principal milestones, equivalent to Nobel Prizes in 2017 and 2020.

Key moments include the first detection of gravitational waves in 2015 – resignation from the combination of two black holes – and weird images captured by the telescope of the event horizon (EHT) in 2019 and 2022. However, none of these observations have to date provided final answers about the nature of loneliness.

Territorial territory

And this restores us to “Leones” Liberati refers to: We can describe the physics of the black hole only to a distance from the center. In addition, he’s lying – the situation of science is unacceptable.

That is why scientists have long been looking for a brand new paradigm, by which the peculiarity is “cured” by quantum effects, which gravity must show in such extreme conditions. This, of course, results in models of black holes without peculiarities, equivalent to those studied in the work of Liberati and his colleagues.

One of the interesting features of the latest article is its common origin. It is neither the work of one research group nor a conventional review article. “It’s something more,” explains Liberati.

“This has emerged from a set of discussions between leading experts in this field – theories and phenomenologists, younger and older researchers – combined during dedicated IFPU workshops. The article is a synthesis of ideas presented and discussed in sessions, which, roughly correspond to the structure of the article itself.”

According to Liberati, the added value consists of the conversation itself: “On several topics, participants initially had divergent views – and some ended sessions with at least partially changed opinions.”

Two non -by alternatives

During this meeting, three principal models of the black hole were outlined: a regular black hole expelled by the classic general relativity, with the horizon of peculiarities and the horizon of the event; An abnormal black hole that eliminates peculiarity, but retains the horizon; and a black hole mimicker, which reproduces the external features of a black hole, but there’s neither peculiarities nor the horizon of the event.

The article also describes how abnormal black holes and followers can form, how they might transform into one another, and most significantly, what statement tests can sooner or later distinguish them from standard black holes.

Although the observations gathered to date were groundbreaking, they do not tell us all the pieces. Since 2015, we have now detected gravitational waves from the fusion of black holes and obtained images of shadows of two black holes: M87* and Sagittarius A*. But these observations only focus outside – they don’t ensure that it’s in the center in the center.

“But not everything is lost,” says Liberati. “Ordinary black holes, especially followers, are never exactly identical to standard black holes – even outside the horizon. So observations that these regions can indirectly tell us something about their inner structure.”

To do that, we could have to measure subtle deviations from Einstein’s theory forecasts, using an increasing number of sophisticated instruments and various statement channels. For example, in the case of followers, high resolution imaging by the event’s horizon telescope may reveal unexpected details in the light inclined around these objects-as more complex photon rings.

Gravitational waves can show subtle anomalies compatible with non -classical space -time geometry. And thermal radiation from the surface of the object with no horizon – like Mimicker – can offer one other promising clue.

Promising future

Current knowledge will not be enough yet to find out exactly what kind of disorders we must always look for or how strong they can be. However, in the coming years, significant progress in theoretical understanding and numerical simulations is predicted. They will put the basis of latest statement tools, designed especially for alternative models.

As it happened with gravitational waves, the theory will conduct statement – after which observing the theory perfectedly, maybe even excluding some hypotheses.

This research line is a big promise: it can assist in the development of quantum theory of gravity, a bridge between general relativity – which describes the universe on large scales – and quantum mechanics that rules the subatomous world.

“What awaits the study of gravity,” sums up Liberati, “It is a really exciting time. We enter the era in which a vast and unexplored landscape opens in front of us.”