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They haven't been ruled out but they are no more likely than wimps, probably not as likely, since most likely masses of PBH have been more or less ruled out by observation, but not all.
originally posted by: pfishy
If PBHs do exist in the theorized quantities, they could explain the gravitational attraction of Dark Matter without the need for new particles that defy all of our attempts to observe or create.
Before 1998 that seemed like a theoretical future possibility, but after 1998 with the discovery of dark energy, it doesn't, it's only a big bang idea. It is reasonable to presume that the supermassive black hole in each galaxy may dominate the galaxy's mass at some very distant future date, and probably mergers of these in local groups of galaxies will happen, but some are already too far apart to merge and are receding faster than the speed of light, and accelerating. I know of no modern theory which would allow such to merge, ever.
theoretically the entire mass of the Universe could be contained in one singularity.
We have made searches for the signatures of evaporating black holes and the searches concluded there can't be very many, so I think we need to look for another explanation for dark energy.
Now, what if, once it passes out of the vicinity of the singularity, the escaped particle reverts to it's previous state of non-existence and returns to the Quantum Energy Background? And if this happens with billions of singularities throughout the universe, could the net gain of energy to the quantum background of the Universe be fuelling the expansion of spacetime? And, since smaller singularities evaporate faster, and without an equal or greater amount of incoming matter and energy to achieve equilibrium with evaporation, the rate of evaporation would accelerate over time, could this not explain the observed acceleration of the expansion of spacetime as well?
Could Black Holes and Hawking Radiation be the answer?
If the mass is less than the moon's mass it can evaporate, and if it's evaporating it's not going to last forever, so the fact we're not seeing the GRBs tells us that if there are black holes evaporating out there, there can't be very many of them and not enough of the evaporating type to account for all dark matter.
originally posted by: pfishy
a reply to: Arbitrageur
The evaporation signalso we were searching for were Gamma Ray Bursts at the very end of the singularity's existence. To my knowledge, there has been no search for the Hawking Radiation itself, due to the fact that it is such a small amount for any singularity we would be able to detect. It could also be that any singularities small enough to have completely evaporated by now have long since done so, but the remaining ones are either in basic equilibrium from absorption of background radiation from various sources, or are just getting to the point where they are getting out of equilibrium.
So, what is the cutoff before an evaporating singularity ends in a GRB? How much mass is converted into that final outburst? Perhaps it is lower amount than we theorize, and the output is just not great enough to detect.
I don't know what you mean by "lay physics community" but professional physicists are divided on the merits of Hawking's latest papers which change the nature of the event horizon but they don't imply that
originally posted by: TarzanBeta
In short, there is no such thing as an event horizon.
Why this isn't more common knowledge in the lay physics community is an intriguing question.
because neutron stars can form with masses of something like 1.4 to maybe 2.5 or so stellar masses and they aren't considered black holes. We think we know the lower mass limit for neutron stars, but we don't really know the upper mass limit, though observations inferring black holes with masses of 3 or so stellar masses suggest neutron stars may not get much bigger than that.
Black hole may be a blanket term for any unified object higher than a star in the universal body heirarchy
One problem is it's not a complete explanation which the authors admit:
Some welcome his latest report as a fresh way to solve a black-hole conundrum; others are unsure of its merits...
Until we have a workable theory of quantum gravity, confirmed by observation, there's going to be some uncertainty on the exact nature of black holes. I don't think physicists widely expect such a theory to contain a singularity, but exactly what it will contain instead, we don't really know, except perhaps that it still has to be more dense than a neutron star and since that's probably the densest form of baryonic matter, the black hole can't be made of baryons as we know them.
the work is incomplete. Abhay Ashtekar, who studies gravitation at Pennsylvania State University in University Park, says that he finds the way that the authors transfer the information to the black hole — which they call ‘soft hair’ — unconvincing. And the authors acknowledge that they do not yet know how the information would subsequently transfer to the Hawking radiation, a further necessary step.