# Is there a theoretical min. size/mass limit to a black hole?

1. Jul 19, 2015

### DDH

Normally a star with a mass several times that of the sun will become a black hole at the end of the lifetime of that star. Can black holes exist with a mass much smaller than that exist? In other words, are black holes with a mass of Jupiter or even Earth exist? Or even much smaller than that?
I can remember having read somewhere that a theory of Stephen Hawking predicts that (small) black holes in time will evaporate. So is there a theoretical limit of mass a black hole should have?
This question arose when some people mentioned that the large hadron collider could create (a) black hole(s).

2. Jul 19, 2015

### syhprum1

There seems to no way that a black hole of less than about five solar masses can form but after a vast period of time one of such mass could evaporate down to Planck mass but the universe is not likely to last that long

3. Jul 19, 2015

### Janus

Staff Emeritus
The smaller the black hole, the "hotter" it is and the faster it evaporates. But that also assumes that it is not replacing it mass from somewhere. The universe is filled with the CMBR at a temperature of 2.725 K. Since black holes can "feed" on radiation just as easily as matter, as long the the temperature of the black hole is less than this, the black hole will take in more than it losses, and it will not shrink. This threshold is somewhere around the mass of the Moon. So if a primordial black hole had formed at at least this size, it would still be around today. A smaller black hole could be stable if it existed in an environment where it was getting even more radiation, near a star for example.

4. Jul 19, 2015

### Chronos

The theoretical minimum mass for a black hole is a Planck mass. It would evaporate in a commensurately brief time - a Planck time. There is no known or theoretical upper mass limit.

5. Jul 20, 2015

### DDH

Thank you all. I've been reading up on several subjects mentioned here, such as Planck mass, Planck distance and Planck time. My question in itself has been answered but at the same time a lot of new questions were raised. A truely humbling experience.

6. Jul 21, 2015

### OmegaOm

According to Stephen Hawking, during the relative short time after the big bang, tiny primordial black holes could of formed in tiny extreme density pockets. These black holes should be around today if true, and evaporate into a xray explosions that could be detected by our instruments. According to our actual measurements of this predicted radiation, it puts one primordial black hole to ever 4 cubic light years which is off the theoretical prediction.

7. Jul 22, 2015

### DDH

Can you elaborate somewhat, please? How did they arrive at the number of one primordial black hole to every 4 cubic lightyears? And is the dispersement uniform?

8. Jul 22, 2015

### Chronos

Its based on the gamma ray background.

9. Jul 22, 2015

### DDH

It has been said that every answered question raises tem new questions. Well, it's happening to me because now i wonder: Is the detected gamma ray background unique for those x-ray explosions, in other words, are there no other processes which could emit that same radiation?
One would expect that because of the expansion of the universe those primordial black holes would be spread out over space. So some explosions should be closer than others thereby giving different signalstrengths. Have those been detected?

10. Jul 23, 2015