Black holes are regions in spacetime with such strong gravitational fields that nothing can escape their boundaries, not even light. As a result, most of these massive objects invisibly drift through space, making it difficult to resolve the many open questions about their mind-bending properties.
Now, scientists have suggested there may be a way to confirm a key mystery about black holes—whether they produce vortex structures—by searching for specific signatures in space. These vortexes would be structurally similar to the swirling maelstroms of tornadoes and whirlpools, but they would arise in multiple places on black holes instead.
In addition to shedding light on black holes, these clues could potentially open “an observational window to various hidden sectors” of the universe, including the nature of dark matter, according to a recent study published in Physical Review Letters.
While popular depictions of black holes often make them look like giant space vortexes, the presence of vorticity in these entities is a matter of debate. Researchers led by Gia Dvali, director at the Max Planck Institute for Physics in Germany, have presented new theoretical evidence that rapidly spinning black holes “naturally support a vortex structure” and that black hole vortexes (also known as vortices) could have “macroscopically observable consequences,” reports the study.
“The microscopic structure of black holes remains to be understood,” Dvali and his colleagues said in the study. “One of the main obstacles is the lack of experimental probes of black hole quantum properties. In this light, it is very important to identify and explore those microscopic theories that lead to macroscopically observable phenomena.”
“We shall create awareness about one such phenomenon: vorticity,” the team added. “We believe that…the vorticity property in black holes can be understood without entering into the technicalities of quantum gravitational computations.”
The new research was partially inspired by experimental studies of Bose–Einstein condensates, an ultracold state of matter with bizarre quantum properties that are useful for modeling black hole behaviors. Many laboratory tests have revealed vortex formation in these condensates, and some models suggest that black holes are Bose–Einstein condensates made of “gravitons,” which are the hypothetical “quanta of spacetime itself,” according to study co-author Florian Kühnel.
“Bose-Einstein condensates as a state of matter are well known to exist in many circumstances, with numerous experimental realizations,” said Kühnel, who is a cosmologist at Ludwig Maximilian University of Munich, in an email to Motherboard. “In those, it has been shown that their fast rotation yields the appearance of vortex structures. We realized this similarity and looked [to see] if vortices also appear in the framework of Bose-Einstein condensates of gravitons—and indeed found them!”
The researchers confirmed the possible presence of black hole vorticity in theoretical models based on the experimental data. The results have many implications—for instance, they might explain why rapidly rotating black holes don’t seem to produce Hawking radiation, a type of thermal glow that is thought to be emitted by some of these objects.
The structures could also lead to extraordinary breakthroughs beyond black holes, including the opportunity to open a “portal into the sector of dark matter,” the study’s authors wrote. Dark matter is a mysterious substance that does not fit into the “standard model” that currently explains our universe.
“Dark matter could be made of particles of extremely small electric charge,” several orders of magnitude smaller than an electron, said Michael Zantedeschi, a PhD researcher at the Max Planck Institute of Physics and a co-author of the study, in an email. “As we show, the interaction of such particles with the black hole vortex would lead to extremely powerful electromagnetic emission from the black hole, which might well be detected.”
“In turn, the absence of such a signal could constrain the spectrum of those beyond-standard-model particles,” Zantedeschi said. “This is a path we surely plan to explore in depth in the future.”
Extremely luminous objects called active galactic nuclei, which are powered by supermassive black holes that sit at the center of large galaxies, could help reveal black hole vorticity and all of its implications. These nuclei shoot out huge jets of plasma that travel close to light speed and can extend across a million light years.
Dvali and his colleagues note that these energetic jets might emit magnetic signatures of vorticity in their light, which could be captured and deciphered in telescope images. The jets are also thought to interact with dark matter. As a result, future observations of jets, and the possible signatures of vortexes within them, could inform the major scientific quest to understand dark matter—among many other applications. Indeed, Kühnel noted that there are a host of questions that could be constrained by the team’s work.
“A very tempting one is to explore under which conditions multiple vortices form since these are known to emerge in laboratory systems,” Kühnel said. “If this indeed turns out to be the case: how are they arranged? Will it be a lattice configuration as observed in laboratories?”
“Then, as regards astrophysical implications, we are currently exploring the generation of magnetic fields from vortical black holes,” he continued. “It seems the vortices can explain the strongest magnetic fields in active galactic nuclei. Furthermore, vortices in so-called primordial black holes (ie. black holes which are produced in the early Universe) could account for the magnetic seeds needed for the observed galactic magnetic fields, thereby solving this conundrum as well as that of the origin of dark matter!”
Update: This article has been updated to include comments from study co-authors Florian Kühnel and Michael Zantedeschi.