Rants And Ramblings About Mobile Technology

For what it’s worth, here’s a conversation with a guy who’s slightly more well-versed in astronomy than I am.

The mobile angle: “In space, no one can hear you scream … because there’s no coverage.”

And no, brane is not the same as brain, but short for the multi-dimensional membrane that supposedly our universe is a side effect of. I wonder how they came up with that theory though.

Question

I read the answer to the question about the size of a black hole (at Curious about Astronomy?), and I'm wondering what the event horizon has to do with the size. I guess it's rather the size of a quark, or even nothing (a real hole in 3D (or higher) space, into the brane). Analogy: When measuring the size of a vacuum cleaner (read: black hole) you don't count the distance at which socks (read: light) are sucked in. Bad analogy, but you get my drift.

Cheers,
Anders

Answer

I love the analogy actually, but the problem is what if you had to use socks to learn about the vacuum cleaner. ie information is carried via socks (light) and so we need to be able to grab some socks to learn about things, then the best we can do is say there is a region from which no socks are ever emitted and to which socks are constantly lost once they enter the region. Then the best we can do is quantify the size of the region, by giving the size of the event horizon. In fact if socks are light then we would never know that what was in fact responsible was a vacuum cleaner, which means further that we cant talk about the size of the vacuum cleaner itself but only the size of the region it impacts.

For this reason we don't actually know the state of matter inside an event horizon it is possible that some new degeneracy pressure kicks in and actually maintains a finite sized ball for a while inside the event horizon, and that as the black hole grows in mass it eventually overcomes the pressure and has a supernova like explosion (but all contained inside the event horizon). However it is most often stated as you have that the size of the actual matter that creates the black hole is actually infinitesimal, ie a true singularity of completely collapsed matter or energy.

Put simply, our ignorance of physics at such matter densities (an ignorance which is not likely going to go away since an event horizon is created at these densities which obscures the events inside it) prevents us from talking about the size of anything but the event horizon.

Hope that helps,
Istvan Laszlo

Question

Thanks for the elaborate response, and continuation of the slightly flawed sock model :).

The reason I asked the question was that I've read articles stating the actual size to be that of a particle (or even nothing) as if it was somehow proven. I understand now it isn't.

Would it be right to say that the radius of the event horizon is proportional (not necessarily linearly) to the mass of the black hole, and that is all that can be measured? What about determining the contents of a black hole (relative quantity of types of particles)? Impossible to know? I figure atoms are torn apart already in neutron stars, so the difference in a black hole _might_ be total collapse, but not necessarily.

Anders

Answer

Yes the event horizon radius is 3 times the mass, if you want radius in kilometers and the mass is given in solar masses. (This is true for a nonrotating blackhole, and is a theoretical result which could be tested but has not yet.

This brings up an interesting point, the size of the singularity is in theory zero ie a true singularity, however this cannot be tested, and anything compressed to a size smaller than the 3M limit of the objects event horizon would be a black hole.

Indeed we cannot really say what kind of particles the matter is in, likely it is not neutrons since neutron degeneracy pressure prevents black hole formation once its over come the main particle constituent may be quarks, but we dont know (in fact it is possible quarks would also prevent black hole formation and need to be destroyed to make a black hole.

So basically as you say atoms are torn apart but to what degree we just don't know.

Hope that helps,
Istvan Laszlo

Well, there you have it.

Posted by Anders Borg 11:20 | Permalink