The event horizon of a black hole is a spherical or spheroidal region from which nothing, not even light, can escape. But outside the event horizon, the black hole is predicted to emit radiation. Hawking’s 1974 work was the first to demonstrate this, and it was arguably his greatest scientific achievement. (NASA; DANA BERRY, SKYWORKS DIGITAL, INC.)

Sorry, Stephen Hawking, But Every Black Hole Is Still Growing, Not Decaying

Hawking radiation should really be happening, but black holes are farther from decaying than ever before.

Black holes are, in many ways, the most extreme objects that will ever exist in our Universe. Typically formed from the deaths of very massive stars, a black hole is where an enormous amount of mass gets concentrated into such a small volume that — within a certain region of space around it — nothing can escape its gravitational pull. Inside what’s known as the black hole’s event horizon, not even light itself can escape from a black hole.

But that doesn’t mean that black holes will live forever; on the contrary, they slowly decay away due to a phenomenon known as Hawking radiation. The stronger the curvature of space is outside the event horizon, the faster the black hole decays away. Based on the black holes that can exist in our Universe, you might wonder how many have either decayed away or are decaying right now. After 13.8 billion years, the surprising answer is zero. Here’s the science of why.

The mass of a black hole is the sole determining factor of the radius of the event horizon, for a non-rotating, isolated black hole. For a black hole of ~1 solar mass, its event horizon would be about 3 kilometers in radius. (SXS TEAM; BOHN ET AL 2015)