One of Stephen Hawking’s most profound messages to humanity is that nothing lasts forever—and, finally, scientists may be ready to prove it.
This idea was carried over from what was perhaps Hawking’s most important work: the hypothesis that black holes “leak” thermal radiation, evaporating in the process and ending their existence with a final explosion. This radiation would eventually become known as “Hawking radiation” after the great scientist. However, to date, it is a concept that remains undiscovered and purely hypothetical. But now, some scientists think they may have found a way to finally change that; perhaps we will soon be on our way to cementing Hawking radiation as fact.
The team suggests that when larger black holes collide and merge catastrophically, small, hot “bites” of black holes can be released into space – and this could be the key.
Importantly, Hawking had said that the smaller the black hole, the faster Hawking radiation will flow. So, supermassive black holes with masses millions or billions of times that of the sun would theoretically take longer than the predicted lifetime of the cosmos to “flow” completely. In other words, how would we detect such an extremely long-lasting leak? Well, maybe we can’t – but when it comes to these asteroid-mass black hole bites, called “Bocconcini di Buchi Neri” in Italian, we might be in luck.
Small black holes like these can evaporate and explode on a time scale that is actually visible to humans. Plus, the end of these black holes’ lifespans should be marked by a signature signal, the team says, indicating their deflation and death via the outflow of Hawking radiation.
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“Hawking predicted that black holes evaporate by emitting particles,” Francesco Sannino, a scientist behind this proposal and a theoretical physicist at the University of Southern Denmark, told Space.com. “We set out to study this and the observational impact of producing many bites of black holes, or ‘Bocconcini di Buchi Neri’, that we imagine form during a catastrophic event such as the merger of two astrophysical black holes.”
Black holes with a bite can’t keep calm
The origin of Hawking radiation dates back to a 1974 paper written by Stephen Hawking called “Black hole explosions?” which was published in Nature. The paper came as Hawking considered the implications of quantum physics in the formalism of black holes, phenomena arising from Albert Einstein’s theory of general relativity. This was interesting because quantum theory and general relativity are two theories that notoriously resist unification, even today.
Hawking radiation has remained worrisome and undetected for 50 years now for two possible reasons – first, most black holes may not emit this thermal radiation at all, and second, if they do, it may not be detectable. Plus, in general, black holes are very strange objects to begin with and therefore complex to study.
“What concerns us is that black holes have temperatures that are inversely proportional to their masses. This means that the more massive they are, the cooler they are, and the less massive they are, the cooler they are. they’re hot,” Sannino said.
Even in the emptiest regions of space, you’ll find temperatures around minus 454 degrees Fahrenheit (minus 270 degrees Celsius). This is due to a uniform field of radiation left over from the Big Bang, called the “cosmic microwave background” or “CMB”. This field if often called a “cosmic fossil”, too, because of how old it is. Furthermore, according to the second law of thermodynamics, heat should not be able to flow from a colder body to a hotter body.
“Black holes heavier than a few solar masses are stable because they are cooler than the CMB,” Sannino said. “Therefore, only the smallest black holes are expected to emit observable Hawking radiation.”
Research author Giacomo Cacciapaglia of the French National Center for Scientific Research told Space.com that, because the vast majority of black holes in today’s universe are of astrophysical origin, with masses several times that of the sun, they cannot emit observable Hawking radiation. .
“Only black holes lighter than the moon can emit Hawking radiation. We propose that this type of black hole can be produced and ejected during a black hole merger and start radiating immediately after its production,” Cacciapaglia added. “Black hole animals would be produced in large numbers in the vicinity of a black hole merger.”
However, these black holes are too small to create effects that allow them to be imaged directly, as the Event Horizon telescope has done for supermassive black holes by focusing on the glowing material surrounding them.
The team suggests that there is a unique signature that could be used to indicate the existence of these bite-sized black holes. This would come in the form of a powerful burst of high-energy radiation called a gamma-ray burst occurring in the same region of the sky where a black hole merger has been detected.
The researchers said that these Bocconcini di Buchi Neri black holes will emit Hawking radiation faster and faster as they lose mass, speeding up their explosive destructions. Those possessing masses of about 20,000 tons would take about 16 years to evaporate, while examples of bite-sized black holes with masses of at least 100,000 kilotons would potentially take up to hundreds of years.
The vaporization and destruction of the particles would produce photons exceeding the trillion electron volt (TeV) energy range. To get an idea of how energetic this is, Sannino said that CERN’s Large Hadron Collider (LHC) in Europe, the largest particle accelerator on the planet, collides head-on with protons with a total energy of 13.6 TeV.
However, researchers have an idea of how to detect these bite-sized black holes as they evaporate. First, black hole mergers can be detected through the emission of gravitational waves, which are tiny ripples in spacetime predicted by Einstein, emitted as objects collide.
Astronomers can then follow these mergers with gamma-ray telescopes, such as the High Altitude Water Cherenkov Gamma-ray Observatory, which can detect photons with energies between 100 Gigaelectron volts (GeV) and 100 TeV.
The team admits that there is a long way to go before the existence of bite-sized black holes can be confirmed, and therefore a long way to go before we can prove Hawking radiation once and for all.
“As this is a new idea, there is much work to be done. We plan to better model the emission of Hawking radiation at high energies beyond the TeV scale, where our knowledge of particle physics becomes less certain, and this will include experimental collaborations in the search for these unique signatures within their data,” Cacciapaglia concluded. “In the longer term, we plan to investigate in detail the production of particles during catastrophic astrophysical events such as black hole mergers.”
The team’s research is available as a pre-print paper in the arXiv repository.
Originally posted on Space.com.
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