All that matters, in the real world, is that something is both massive and compact enough so that, within a certain radius, light cannot escape from it. That is the astrophysical definition of a black hole. –me
We’ve been talking about black holes a lot recently, and with good reason. They’re fun to think about. These objects that collect matter, energy, light, and anything else that dares to cross its event horizon. It’s only natural to ask what might lie beneath that dark area that no light ever escapes from.
In 1916, everyone assumed that whatever happened inside a black hole, it must be powerful enough to simply destroy everything inside of it, and crush everything down to a singularity.
But this isn’t necessarily true, and I’m going to show you a simple example of how you can have a black hole, using only known physics, that doesn’t have a singularity at all.
Above is an artist’s rendition of a neutron star. A neutron star is an object that’s about the mass of our Sun, but with a radius of only around 5 kilometers. Well, if we could get that radius down to about 3 kilometers, no light would be able to get out.
That’s the definition of a black hole. A neutron star is already really, really close! Well, what are neutrons made out of?
Quarks. Specifically, three of them: two down quarks and one up quark. Down and up are the two lightest quarks that we know of, and so the neutron has a total energy of about 1 GeV. But we know of six quarks, and we have many different combinations that could make a neutral particle just like a neutron.
Let’s say, instead of two down quarks, we just replaced one of the down quarks with a bottom quark. Why do I pick this combination of “up-down-bottom”? Because we’ve discovered it, and it’s about six times as massive as a neutron. You make a star the mass of the Sun out of those, and do you know what happens?
Your density goes up, and your volume goes down. If you’re suddenly smaller than a neutron star, it only makes sense to ask “by how much?”
Well, if every particle is six times as massive, then you only need one-sixth the number of them, so your radius is ³√(6) times smaller than a neutron star. How big would this “bottom”-neutron star be? Only 2.75 kilometers in radius! In other words, it would be a black hole, and no light would ever get out!
And there’s no need to have a singularity, it would just be like a plain-old neutron star in every way, except it would be just a little denser than normal. And that’s just one of many simple possibilities! Have a great Thanksgiving, and I’ll see you all soon!