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A Black Hole Doesn't Die -- It Does Something A Lot Weirder

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Black holes are basically "game over, man," for anything that gets too close to them, but they aren't invincible. In fact, they're always in the process of self-destructing. We'll look at how they fizzle out, and see if we can help them do it faster.

The Event Horizon

Realistically speaking, you are dead as soon as you get anywhere near a black hole. You'll be snapped like a rubber band by the differences in the gravitational pull on your top and bottom half, or you'll be fried by radiation (more on that later). No one in the foreseeable future (even if we try to foresee multiple millennia into the future) will get close to a black hole. Pass the event horizon, however, and you don't even have an unforeseeable future. Once material gets beyond the event horizon, it's being pulled into the black hole with such force that it doesn't escape. Not even light gets out. Once something has gone beyond the event horizon, it no longer really "counts" as part of the universe anymore.


The event horizon is the scariest part of the black hole. It's also the reason that every black hole dies. In the world of quantum mechanics, the universe has an ace up its sleeve in what's come to be known as Hawking radiation.


Particles and Antiparticles That Pop Up From Nothing

For something that contains so much emptiness, the universe is surprisingly full. Black holes are not holes. They're giant bundles of extremely dense matter. Even stretches of empty space aren't quite the nothingness they appear to be. Particles appear and disappear inside of them all the time. Why?

The explanation starts with quantum tunneling. Particles have been known to suddenly appear on the far side of barriers they shouldn't be able to breach, thanks to the Heisenberg uncertainty principle. The closer we pin down a particle's position, the more wildly its momentum may vary. If we know its momentum, its position may vary. Get a particle close to a barrier, and it may suddenly have the blast of momentum it requires to tunnel through. This blast of momentum is also a blast of energy. And energy, and matter, are one and the same according to Einstein. If energy can suddenly appear, so can matter. And the closer we look at space, the more confined the area we look at, the more we should see matter popping into being.


We don't see huge chunks of matter spontaneously appearing because, when a particle is created, its antiparticle is created at the same time. Touch the two together, and they annihilate. Sure, sometimes they drift away from each other and survive for a while, but it can't happen often. Their extreme temporary status has caused scientists to sometimes call them virtual particles.

Hawking Radiation and Dissolving Black Holes


Unless this creation of two virtual particles happens right at the event horizon of a black hole. If a particle and its antiparticle pop into being on the event horizon, one gets sucked in. The other gets away. If the antiparticle gets sucked into the black hole, and the particle breaks free, the particle no longer has a chance to annihilate. It is now real, and not virtual. Its presence and energy count in the universe. And real radiation leaking from a black hole means that the black hole itself is slowly shrinking. This radiation, suggested by Stephen Hawking and called Hawking radiation, might allow a black hole to waste away over time.

How much difference can single particles make? Hawking himself thinks they make so much of a difference that the definition of "black hole" needs to change. Black holes don't have an event horizon. They have an "apparent horizon." The edge of the black hole causes quantum effects to go wild, the virtual particles that pop into being cause the apparent horizon to fluctuate, and the entire thing is more of a flickering, growing, and shrinking mess than we give it credit for. Enough of this fluctuation of the horizon, and the black hole can fizzle out.


Even with all the Hawking radiation and the flickering apparent horizon, it would take a long, long time for a black hole to disappear. A black hole the size of Earth's sun will take many billions of times the current age of the universe to disappear entirely. And even if we were to get a device to stimulate making of matter-antimatter pairs, there is no way to get it to the apparent horizon safely, so we can't help it along. Still, there's a chink in their armor. Black holes aren't forever.

Top Image: Felipe Esquivel Reed

Second Image: Chandra Observatory

[Via Nature, Scitable, Hawking Radiation Poses New Questions, New Scientist, Into the Black Hole, Quantum Tunneling.]