New research suggests that there is a 90% chance that within the next decade, humanity could use a space or Earth-based telescope to spot an exploding black hole. Such a detection would change our perspective of the universe by proving the existence of “primordial black holes” born 13.8 billion years ago, a second after the Big Bang.
Scientists have long suspected that black holes can explode, but that the length of time this takes increases in step with the mass of any black hole. Previous estimates have suggested that the largest possible black holes would take longer than the hypothesized lifetime of the universe to explode. Such an explosion would happen to the smallest possible black holes, at most, once every 100,000 years, according to previous theories.
However, the team behind this new study put forward a new model of the electric charge of black holes, which they call a “dark-QED toy model.” This model includes a very heavy, hypothesized version of the electron, which the team has dubbed a “dark electron.” If that model is correct, then a primordial black hole explosion could be witnessed once every 10 years.
An explosion of a primordial black hole is theorized to flood the universe with all possible particles. That would include the established particles of the standard model of particle physics, electrons, quarks, and Higgs Bosons, as well as the particles beyond the standard model, such as the particles that could make up dark matter.
That means spotting such an explosion could not only reveal the existence of primordial black holes, but it could also solve a wealth of puzzles regarding particles beyond the standard model.
“We’re not claiming that it’s absolutely going to happen this decade, but there could be a 90% chance that it does,” team member Michael Baker of the University of Massachusetts, Amherst, said in a statement. “Since we already have the technology to observe these explosions, we should be ready.”
Do black holes ‘leak’?
Black holes come in a range of masses, and that fact is integral to the team’s theory.
Perhaps the most familiar concept of black holes is the so-called stellar mass black hole, with masses between 10 and 1,000 times the mass of the sun. These black holes are born when massive stars reach the end of their nuclear fuel and can no longer support themselves against their own inward gravitational pull. This results in a region of spacetime with a gravitational influence so great that not even light is fast enough to escape it (putting the “black” in black holes).
With masses equivalent to millions or even billions of suns, supermassive black holes are too massive to have been born from dying stars; instead, it is theorized that they are created when smaller black holes collide and merge, and a chain of progressively larger and larger mergers.
Primordial black holes, meanwhile, are theorized to be much more diminutive than even stellar mass black holes, with masses predicted to be anywhere from that of giant planets down to average-sized asteroids. Primordial black holes are theorized to have been created not from stars but as a result of initial density fluctuations in the universe moments after the Big Bang.
The concept of exploding black holes originated in 1974 when Stephen Hawking, the British physicist and science communicator, suggested that black holes “leak” a type of thermal radiation that would later be dubbed “Hawking radiation.”
The emission of Hawking radiation would cause the black hole to gradually evaporate, with this process ending with an explosion. The temperature of this radiation depends on the mass of the black hole emitting it, but this is an inverse relationship; the bigger the black hole mass, the lower the “Hawking temperature.” That would also mean that smaller black holes are much hotter than the space around them, meaning they radiate Hawking radiation much more rapidly, losing their already smaller mass more quickly than monstrously massive black holes.
And this is how scientists say we should be able to spot them. “The lighter a black hole is, the hotter it should be and the more particles it will emit. As primordial black holes evaporate, they become ever lighter, and so hotter, emitting even more radiation in a runaway process until explosion,” team member and UMass Amherst researcher Andrae Thamm said. “It’s that Hawking radiation that our telescopes can detect.”
Therefore, astronomers should be able to detect primordial black holes, but if they exist, they’ve thus far proved elusive.
“We know how to observe Hawking radiation,” team member and UMass Amherst researcher Joaquim Iguaz Juan said. “We can see it with our current crop of telescopes, and because the only black holes that can explode today or in the near future are these primordial black holes, we know that if we see Hawking radiation, we are seeing an exploding primordial black hole.”
Previously, the chance of detecting an exploding primordial black hole has been deemed infinitesimally small; however, as Iguaz Juan pointed out, “our job as physicists is to question the received assumptions, to ask better questions and come up with more precise hypotheses.”
The team questioned assumptions by reconsidering what is theorized about the electric charge of black holes. Stellar mass black holes are considered to be electrically neutral, and until now, primordial black holes were theorized to be the same.
“We make a different assumption,” Baker said. “We show that if a primordial black hole is formed with a small dark electric charge, then the toy model predicts that it should be temporarily stabilized before finally exploding.”
That results in a primordial black hole explosion occurring on average once every 10 years rather than once every 100,000 years.
The next step for the team is to get ready to make such a detection and take advantage of what they predict is a 90% chance of a primordial black hole exploding.
“This would be the first-ever direct observation of both Hawking radiation and a PBH. We would also get a definitive record of every particle that makes up everything in the universe,” Iguaz Juan said. “It would completely revolutionize physics and help us rewrite the history of the universe.”
The team’s research was published on Wednesday (Sept. 10) in the journal Physical Review Letters.