4 ms·
? I thought it was the mass that made a black hole - not the density?
by troels 15y ago
? I thought it was the mass that made a black hole - not the density?
- adrianN 15y agoNo, you just require a sufficient pressure to overcome the repulsive forces between the particles to collapse them to a singularity. That's why people were afraid of the LHC.
- troels 15y agoAh .. And normally (If that is a word which makes sense in this context), the mass of a giant object (Like a star) would be the way to create this pressure? But theoretically you could do it by other means?
- weavejester 15y agoYou essentially need to cram a lot of mass into a very small space, which is equivalent to cramming a lot of energy into a very small space. So, theoretically, you can get a bunch of very, very large lasers, focus them all upon a very small point, and if you pump enough energy into the system you wind up with a black hole.
- lutorm 15y ago"just"... Nuclear matter is very stiff. It can make a mass of the order of the Sun's, falling down with a significant fraction of the speed of light, bounce without becoming a black hole. So the pressure you'd need to make a black hole with higher-than-nuclear density would be, well, astronomical.
- billswift 15y agoYou need sufficient mass for a black hole to be stable, otherwise it "evaporates". A very small black hole would evaporate so fast that "explodes" would be a better term.
- Confusion 15y agoThere is a minimum amount of mass necessary for an object to be able to collapse upon itself and form a black hole, such as a large star does when the outward pressure due to the internal fusion reaction stalls. However, any amount of mass can (in classical theory) be compressed far enough to obtain a Schwarzschild radius, from which light cannot escape. This has only to do with the density, not the total mass: a very small mass can still cause a large curvature of space, though only in a very small region of space.
- troels 15y agoOK, now that we're already discussing this topic. I just read this quote from Wikipedia: """If one accumulates matter at nuclear density (the density of the nucleus of an atom, about 1018 kg/m3; neutron stars also reach this density), such an accumulation would fall within its own Schwarzschild radius at about 3 solar masses and thus would be a stellar black hole.""" I take that to mean that if I wanted to create a black hole of something with less mass than 3 suns, I would have to compress it beyond the density of an atom nucleus? Is this - even in theory - possible to do? Wouldn't you need some kind of "magic wand" (to stick with the articles authors choice of words?)
- pavel_lishin 15y agoI have strep throat and may not be at my best right now, but iirc the chandrasekhar limit is 1.5 solar masses - it's enough to form a black hole because not only is there a lot of mass, but it's also falling into the center, compressing everything further. So one of your "magic wand" options is acceleration, I think.
- Confusion 15y agoWell, that is why I said 'classical theory' :). I have no clue whether QM allows it and I don't think anyone does: that would amount to knowing the true nature of the 'singularity' inside a black hole.
- jules 15y agoSo you could say that all point masses (e.g. electrons) are black holes? What happens if you take a large black hole, and you throw a lot of electrons into it? Does it get an electric field measurable from the outside? If not, how come an electron does have this field?