Could there be a black hole inside the sun?

Could there be a black hole inside the sun?

It’s a classic story of apocalyptic fiction. The Sun, our precious source of heat and light, collapses to form a black hole. Or maybe a stray black hole comes along and swallows him up. The end is near! If a stellar-mass black hole swallowed our sun, we’d only have about 8 minutes before it became real, the kids say. But suppose the Sun swallowed a small primordial black hole? Then things get interesting, and this is definitely worth writing a paper about arXiv.

Primordial black holes are hypothetical black holes that formed during the first moments of the universe. Unlike stellar-mass black holes or supermassive black holes, primordial black holes are usually small, with a mass roughly the mass of an asteroid and a size smaller than a baseball. They appear in some theoretical models, and have been used to try to explain everything from dark matter to the distant Planet X. Many of these models claim that primordial black holes are common, so it’s inevitable that a star will eventually capture one. These stars with a central black hole are known as Hawking stars.

As this new work suggests, the captured primordial black hole would initially have almost no impact on a Sun-like star. Compared to the mass of the Sun, the mass of the asteroid might also be a speck of dust. Even if it were a black hole, it wouldn’t be able to consume so much sun so quickly. But it will affect things over time. A black hole in a star would consume the material in the star’s core and grow over time. If it could grow so quickly on a cosmic level, it could consume an entire star. If not, it could still affect the star’s evolution and end of life.

Mercury’s black spot, along with a group of individual sunspots, is currently heading toward Earth. Image credit and copyright: @Blobrana

The study shows that it is largely due to the initial size of the primordial black hole. For those in the larger mass range that observations don’t rule out, about a billionth of the Sun’s mass, they could consume a star in less than half a billion years. If this happened, there should be solar-mass black holes, which are too small to form from supernovas like conventional stellar-mass black holes.

If the primordial black hole was much smaller, say less than a trillion Sun masses, things get more complicated. The mini black hole will consume some of the matter inside the star, but not at a rapid pace. However, it will move things around in the core, heating them up more than fusion alone. As a result, the star could swell into a “red stray star” that would be cooler and redder than typical red giant stars. All this turmoil in the core can also affect the star’s surface activity. The effects may be subtle, but the authors point out that the existence of a primordial black hole can be seen through stellar seismology.

Based on our studies in helioseismology, it is almost certain that there is no black hole in our Sun. Or if it exists, it must be very small. So there’s no need to pack your own bag for a solar doomsday. But there might be some Hawking stars if we only care to look.

(^1): Kaplan, Matthew E., Earl B. Bellinger, and Andrew D. Santarelli. “Is there a black hole in the center of the sun?” arXiv preprint arXiv:2312.07647 (2023).

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