I Is there a plan for a search for nearby black holes?

[Monsterboy]

Hi JMz:

I read somewhere (sorry, I don't remember where) that any primordial BHs would have already evaporated a long time ago.

That's why I asked the question of the "minimum feasible mass" of a black hole which will allow it to not evaporate due to hawking radiation, given the current intensity of CMB.

What is the minimum feasible mass of a black hole which will allow it to exist without losing mass due to hawking radiation ? Given that, the only source of energy for the black hole is the CMB i.e energy lost due to hawking radiation = energy gained by absorbing the CMB radiation.

If this mass less than one solar mass( most probably much much less), then the probability of finding a black hole of this mass will be very very low. But if we ever find such a black hole (or make one ?) or a less massive one, it might answer two questions.
1. Is Hawking Radiation real ? If it isn't then will never find a black hole that small or close to that.
2. Are PBHs responsible for dark matter ? If we find one such black hole, there might be billions of others spread out throughout the galaxy

 

[Chronos]

The mass fraction of dark matter that could consist of PBH's is constrained to about 10% as discussed here; https://arxiv.org/abs/1705.05567, Primordial black hole constraints for extended mass functions. This is actually tighter than the usual constraints based on monochromatic mass distributions.

 

[glappkaeft]

That's why I asked the question of the "minimum feasible mass" of a black hole which will allow it to not evaporate due to hawking radiation, given the current intensity of CMB.

https://www.physicsforums.com/threads/black-holes-and-hawking-radiation.860484/#post-5403327

 

[T Y Thomas Jr]

The GAIA mission is the biggest project currently underway. The first data release milestone was achieved in 2016 with; https://arxiv.org/abs/1609.04303,Gaia Data Release 1: Astrometry - one billion positions, two million proper motions and parallaxes This monumental endeavor will catalog over a billion stars in the MW, along with a number of extragalactic sources - including over 500,000 quasars. Its limiting magnitude is 20.5 and will reach stars in the MW core. The odds of it revealing hitherto undiscovered black holes in the solar neighborhood are considered very favorable. IRAC ans SWIFT have, and will continue to contribute to the observational databese as well. Our knowledge of compact stars will be significantly expanded by these missions over the next decade as researchers sift through this mountain of new data pouring in. Given current knowledge of the abundance of high mass [8+ solar] stars in the solar neighborhood, the odds of finding 125 black hole candidates within 100 light years do not appear promising.

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But I tried to see it. Thanks anyway. T Y Thomas Jr

 

[Monsterboy]

Well, everything about PBH is unknown since it is unknown if they exist at all...

How would we even know whether we are looking at a primordial black hole or a regular one caused by star collapse ? If a PBH has survived till today there is a good chance that it would also be surrounded by other stuff which make an accretion disk or something. It might look just like any other black hole right ?

 

[JMz]

How would we even know whether we are looking at a primordial black hole or a regular one caused by star collapse ? If a PBH has survived till today there is a good chance that it would also be surrounded by other stuff which make an accretion disk or something. It might look just like any other black hole right ?

That's about right. The one noticeable difference is that star-collapse BH's will generally have at least ~ 1 Solar mass or somewhat more. PBH's may have formed with a much larger range of masses, including ones that are small enough to be evaporating right now.