04-26-2021, 01:46 AM (This post was last modified: 04-26-2021, 01:47 AM by Bear.)
Also, when I hear "smallest and closest" my brain immediately says "probably not a coincidence."
Instead, I think, we may see this as the nearest black hole because such small objects may be the most ubiquitous kind of black hole. If they are, then one of them is the nearest black hole to virtually everyplace, and we just don't know it yet! These are right at the limit of our ability to detect. there could be a dozen of them closer and we wouldn't have seen them yet, just because we haven't been searching for them, or haven't been *able* to search for them, until now.
(04-26-2021, 01:18 AM)Bear Wrote: So it's.... what, 1500LY? So, someplace that, in-story, people would reach about 3K years from now? At that date I don't think it's going to be the very first starlifting project, but it would certainly be notable as the first highly-efficient starlifting project taking advantage of tidal energy generated by a black hole.
The first probes would probably reach it during the Version War, 4400 AT or a bit earlier; but the War would probably delay any major engineering works until the ComEmp period. Note that we are seeing it as it was 1500 years ago, and when the Terragen probes get there it will be 5900 years older in its own frame of reference. Is that enough time to develop an accretion disk? I'll assume not.
The Schwarzschild Radius of this 'hole is about 8km, so the event horizon is 16km across. The visible part of the black hole in my image was generated in Space engine. from a distance of about 20,000km, and the spacetime distortion (and Einstein arcs) are easily visible.
(04-26-2021, 01:46 AM)Bear Wrote: Also, when I hear "smallest and closest" my brain immediately says "probably not a coincidence."
Instead, I think, we may see this as the nearest black hole because such small objects may be the most ubiquitous kind of black hole. If they are, then one of them is the nearest black hole to virtually everyplace, and we just don't know it yet! These are right at the limit of our ability to detect. there could be a dozen of them closer and we wouldn't have seen them yet, just because we haven't been searching for them, or haven't been *able* to search for them, until now.
I think 3 solar masses is pretty close to the smallest black hole that it's possible to have appear by natural means. They normally arise in supernovae, IIRC; anything smaller wouldn't be a black hole but a neutron or quark star instead.
The lower mass limit of a black hole is related to the Tolman-Oppemheimer-Volkoff limit, the highest mass for a neutron star. Since there is at least one pulsar with a mass of 2.74 Sol, the smallest black hole is likely to be greater than that. But there are other uncertainties; such as - does the star lose mass-energy when it collapses into a black hole? https://en.wikipedia.org/wiki/Tolman%E2%...koff_limit
I'm thinking the lowerbound limit could also be affected by the rate of spin of the object involved. First there are time dilation effects due to the tangential velocity of the outer shell; second, there is centripetal acceleration away from the axis of spin which could interfere with the negative radial acceleration of gravity; third there is energy expressed as angular momentum which causes gravity just as though it were mass instead of energy.
Fourth it is not clear (to me anyway) whether centripetal acceleration and angular velocity even work the same way at the bottom of a gravity well dense enough to affect the passage of time. I presume relativity means they have the same relationship regardless of our frame of reference. But radial velocity is inversely proportionate to time and centripetal acceleration is inversely proportional to the square of time, so what properties of the relationship does relativity preserve and what do they mean relative to one another as the swarzchild radius or event horizon is approached?
My knowledge of physics isn't good enough to work out the math and say what the effect of spin would be; but I strongly suspect the rotational energy of the body in question is likely to affect its radius of collapse.
It does seem to be important. The fuzziness around the lower limit of black hole formation appears to be largely due to the different amounts of angular momentum each collapsing object possesses. And unlike rest mass, angular momentum can be usefully extracted from a stellar-mass black hole after its formation.
