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“Most black holes are formed when stars collapse,” Ivy said. “But there’s a theory that some of them were created shortly after the Big Bang. The un
by ceequof 11y ago
“Most black holes are formed when stars collapse,” Ivy said.
“But there’s a theory that some of them were created shortly
after the Big Bang. The universe was lumpy. Some of the lumps
might have been dense enough to undergo gravitational
collapse. They could form black holes that instead of
weighing what a star weighs could be a lot smaller.”
“How small?”
“I don’t think there’s a lower limit.”
Yes there is. Black holes lose mass by Hawking radiation: http://en.wikipedia.org/wiki/Hawking_radiation http://en.wikipedia.org/wiki/Hawking_radiation
A black hole smaller than 0.8% Earth masses loses more mass than it gains from the cosmic microwave background, and will eventually evaporate.
- Tloewald 11y agoThat doesn't create a lower limit, just a life expectancy. And the life expectancy is still very long — "within the lifespan of the universe" http://en.m.wikipedia.org/wiki/Micro_black_hole http://en.m.wikipedia.org/wiki/Micro_black_hole
- ceequof 11y agoYou are mistaken. http://arxiv.org/abs/0908.1803v1 http://arxiv.org/abs/0908.1803v1 (See the table on page 15) The lifespan of a 108,000 tonne black hole is ~350 hours. At that mass, its event horizon is .32 attometres across, and the Hawking radiation it emits is measured in gigaelectronvolts.
- Tloewald 11y ago350h is a lifespan, and you're quoting a speculative paper. I haven't read the story extract, but I assume the plan would be to bleed matter into the micro black hole to maintain it. (Arthur C Clarke posited the same concept 40 odd years ago in his Imperial Earth novels.) I assume your point is that a GeV is a minuscule amount of energy, which isn't going to push 130kT around at any speed.
- ceequof 11y agoyou're quoting a speculative paper. Hawking radiation has never been directly observed, but it is generally presumed to exist. I haven't read the story extract, but I assume the plan would be to bleed matter into the micro black hole to maintain it. Read the story. In context, the character is talking about how small a natural, primordial black hole can be. There is an obvious lower bound, due to Hawking radiation. I assume your point is that a GeV is a minuscule amount of energy, which isn't going to push 130kT around at any speed. Read the paper. That's the pseudotemperature of the event horizon. It's so hot that it's glowing largely in ultraenergetic gamma rays. The total power radiated by a .32 attometre black hole is 5,519 petawatts.