Smallest Black Hole

[petrushkagoogol]

What is the size of the smallest black hole that can exist independently ?

[sanctus]

For how long do they have to exist independently? https://en.wikipedia.org/wiki/Micro_black_hole

[CraigD]

What is the size of the smallest black hole that can exist independently ?

According to the theoretical prediction of Hawking radiation, a black hole of any mass can “exist independently” – that is, without relying on in falling mass-energy – but will lose mass-energy at a rate inversely proportional to the square of its mass (m²). This and some complicated math and simplifying assumptions, gives black holes “evaporating” in a time proportional to the cube of their mass (m³).

 

However, the universe has at least a little radiation – the CMBR – everywhere, so a better question, I think, is “what is the smallest black hole that can exist under ordinary conditions, far from other bodies?”

 

Calculating the answer to this question shows that a black hole with a mass of less than about 4 x 10²² kg – about the mass of the Moon – would lose mass and eventually evaporate, while one larger will gain mass and not. A much smaller BH with a mass less than about 10¹¹ kg would evaporate in less than 13,800,000,000 years, about the current age of the universe. A BH less than about 100000 kg would evaporate in less than 1 second.

 

Black holes this small can’t be formed in the usual way – the collapse of a star. The only theoretical explanation for how they could form is in the early history of the universe. Because the final moments of a black hole evaporating would be a very energetic event, astronomers have been searching for decades for signs of one of these primordial black holes evaporating, but so far, not detected any.