Well, here’s a question I never thought could seriously be asked: Could the Sun have a black hole inside it? 

Your first thought is likely to be, “No, DUH”. A black hole has a minimum mass of three times the Sun’s, and we’d probably notice if the Sun were four times more massive than it is now. Plus there’s the whole problem with the black hole gobbling down matter and likely shredding the Sun pretty rapidly.

But that’s for a stellar-mass black hole, one created when a massive star explodes. There’s a smaller kind. Well, maybe. They’re theoretical, but it’s posited that during the moments after the Big Bang, matter was so dense and pressure so high that local fluctuations in density could compress a small amount of matter smaller than its event horizon, so it would create a black hole directly. Mini black holes!

Stephen Hawking showed that it’s likely that primordial black holes (or PBHs) like these would actually emit radiation and explode shortly after they formed, if they’re small enough. Basically, they’re so small they are dominated by quantum mechanical effects like the uncertainty principle, and behave in weird ways (like radiating and exploding).

The larger they are, the slower they emit, so, critically, above a certain mass they’d be big enough to escape that fate for a long time, even billions of years. If it were roughly 10^-16 times the Sun’s mass (a tenth of a quadrillionth), or roughly the mass of a small asteroid, they’d be stable for billions of years. Longer than the current age of the Universe, in fact.

If one of those were inside the Sun we might not notice. It would small, less than a nanometer across, or about the size of a hydrogen atom, so even if it were in the middle of the Sun it would feel like it was in a near-vacuum (the density of the Sun is about 150 grams per cc in its core, which is high by human standards, but we’re talking quantumly small here for physical sizes and distances between particles in the core). The gravity of the black hole is fierce if you’re close enough, but a stray proton or neutron would have to be pretty close to get pulled in. It would happen very slowly.

If the Sun had one of these wee beasts in its belly, what would happen?

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