Most people think that black holes can only absorb, but how true is this? Is it possible for black holes to explode?
Black holes are cosmic “vacuum cleaners”: massive objects that even light cannot escape.
If an “explosion” is a “sudden, brief release of enormous energy,” then we can say that black holes really do explode. The most interesting thing is that they can explode in several ways, namely by blowing up themselves or the surrounding environment.
There is one way that black holes can explode. This process is related to the fact that black holes are not completely black, which was discovered by the famous astrophysicist Stephen Hawking in 1976.
“In classical physics, nothing can come out of a black hole,” Ohio State University physicist Samir Mathur told Live Science, “but Hawking discovered that through quantum mechanics, the hole slowly releases its energy to infinity by emitting low-energy radiation. This is called Hawking radiation.”
Until a black hole absorbs new material, it slowly loses mass due to Hawking radiation. However, Hawking radiation is emitted slowly. A typical black hole several times the mass of the Sun emits about one photon per year. At this rate, it would take a typical black hole 10^100 years to disappear.
But Hawking realized that small black holes disappear much faster. As a black hole becomes smaller and smaller, it emits more radiation. In its final moments of life, a black hole emits so much radiation, and so fast, that it effectively acts as a bomb, releasing high-energy radiation and particles.
If small, Earth-sized black holes had formed in the early universe, they would have taken several billion years to dissipate, meaning that these “primordial” black holes, if they existed, would now be exploding across the universe.
Astronomers have yet to find any evidence of exploding primordial black holes, although they may indeed exist.
Black holes explode in a way that cannot be seen anywhere else in the universe, thanks to their rotation. Rotating black holes—also called Kerr black holes, after New Zealand mathematician Roy Kerr, who first discovered how they work—create an ergosphere around themselves. The ergosphere is an elongated region of space where nothing is stationary. Anything that falls towards a rotating black hole begins to rotate around it as the particle enters the ergosphere.
Spacetime orbiting a black hole can also absorb photons. If there are enough photons, they can bounce off each other or any other particle. Sometimes this kind of ejection throws photons out of the ergosphere, but sometimes the opposite happens — the photons are absorbed even deeper into the black hole, where they gain energy. They can scatter again to a higher orbit, and then return again.
With each iteration of the process and each trip around the black hole, the photon gains energy. This process is called “superradiation”. If the photon is finally released, it will have an enormous amount of energy compared to the initial stage of its journey.
If enough photons are involved in this process, they explode at once with incredible energy, becoming what is known as a “black hole bomb.” Although the black hole itself does not explode, this superadditive effect shows once again how powerful black holes are in their environment.
Disks and a thin jet
The most common way black holes cause explosions is not by their self-destruction, but by their immense gravitational pull. Supermassive black holes are at the centers of galaxies, and sometimes large clumps of matter, such as stars, come too close to them. When this happens, the star is torn apart by tidal effects, and this disintegration process releases energy. Astronomers see this release of energy as a brief but intense flash of X-rays and gamma rays.
In addition to shredding stars, these supermassive black holes often collect “clumps” of matter that constantly swirl around them in giant accretion disks. Accretion disks reach temperatures of a quadrillion degrees, making them the most luminous objects in the universe—a single glowing disk is brighter than a million galaxies at once.
At their most powerful, the discs spin electric and magnetic fields that carry some of the disc material around the black holes and out in long, thin jets that resemble jet trails and reach tens of thousands of light years.
Although these thin jets are not technically explosions, they are still quite intense.