# Blackholes In The Early Universe

1. Feb 22, 2010

### E=mc^84

Would it not be possible for many blackholes to form in the begining stages of the universe since the universe was very dense? Can that be the cause of the so called "Dark Energy" or "Dark Matter"?

2. Feb 22, 2010

### sylas

It is not simply the matter density that makes formation of small black holes possible in the early universe, but rather the massive amounts of energy.

However, whether small black holes were actually formed or not, this is not possible as an explanation for dark energy or dark matter.

Small black holes evaporate very rapidly and explosively; so they are not "dark". Larger black holes can't make up the "halos" of dark matter that exist around galaxies. And they are nothing at all to do with dark energy, which is completely different from matter, or black holes.

Felicitations -- sylas

3. Feb 22, 2010

### E=mc^84

So, then u agree that blackholes are a possibility in the early universe

4. Feb 22, 2010

### sylas

Yes.

5. Feb 22, 2010

### Skolon

Hawking radiation is a proved theory? Many times it is used as a true fact. But it really is?
Sorry for my ignorance!

6. Feb 22, 2010

### sylas

It's a theoretical consequence of what we think physics is like. We don't have a black hole available to test, but it would break some pretty fundamental ideas in physics if there was no Hawking radiation.

7. Feb 22, 2010

### bapowell

It's possible that primordial black holes (PBH) formed out of the initial density perturbations set up by inflation. Black holes would result from regions in the universe with comparatively large overdensities (or comparatively small expansion rates). In most models, these black holes begin to form when the seed perturbation re-enters the horizon after inflation -- and so the mass of the black hole is characteristic of the size of particle horizon at that time. This gives a fairly wide range of possible black hole masses: those formed early (just after the Planck time) are just fractions of a gram, however, those formed later can be much larger ($$10^5$$ solar masses).

Light black holes (with masses less than $$10^{15}$$ grams) will have evaporated via Hawking radiation by the current epoch. However, those heavier guys may well still be around. So, finally getting to your question, I think yes, there has been some work done on determining whether primordial black holes might contribute (in part or in whole) to the dark matter density. Here are two references I fished off spires (I haven't looked them over closely, admittedly).

http://arxiv.org/abs/astro-ph/0302035" [Broken]

http://arxiv.org/abs/1001.2308" [Broken]

The claim that PBH's make up all the dark matter seems a little difficult to make work, since it's pretty clear that we need some form of weakly interacting dark matter to get structure formation to work right. But, perhaps they suggest a way around this in the paper...

Last edited by a moderator: May 4, 2017
8. Feb 22, 2010

### Skolon

Is suppose that LHC will create some mini black holes. Then we will really know is Hawking radiation exist. I very hope he was right! But if he's not? :surprised

But I think we can be calm because if he is wrong the Earth stop to exist log time ago. In upper atmosphere exist much stronger collisions that LHC's. So, a lot of little BH were created in time.

9. Feb 22, 2010

### bapowell

Fear not Skolon. Black holes produced by the LHC will be tiny and harmless. Even if they don't evaporate, they won't eat the earth.

10. Feb 22, 2010

### Skolon

Really? Why is that? Because are very little and have large speed, so it will escape from Earth gravitational attraction? Or else?

11. Feb 22, 2010

### bapowell

Yes. They are tiny. They will not wander around vacuuming up the earth. Since they have a small mass, they have a tiny event horizon. Of course, if a hapless electron meanders into the path of the BH, it will get sucked in. And yes, eventually we can expect the BH to just wander off into space. It might gorge itself on elementary particles before this happens, but nothing more significant.

12. Feb 22, 2010

### E=mc^84

So, what i read so far is that we cannot really know for certain if blackholes formed in the early universe until it is fully tested. But, the next approaching question would be: How would these blackholes distribute themselves in the universe today if they were created in the beginning stages of the universe?

Note: I am assuming that the blackholes were created in the initial stages in the formation of the universe.

Last edited by a moderator: May 4, 2017
13. Feb 23, 2010

### E=mc^84

Thanks for the article, it is very interesting.....

14. Feb 23, 2010

### E=mc^84

Thanks for the article, it is very interesting.....

Last edited by a moderator: May 4, 2017
15. Feb 23, 2010

### Chalnoth

Well, it's pretty darned unlikely that black holes will be produced at the LHC.

Basically, if it were possible for the LHC to produce black holes, then lots of them would be produced in our atmosphere every day.

16. Feb 23, 2010

### E=mc^84

How would these blackholes distribute themselves in the universe today if they were created in the beginning stages of the universe?

Note: I am assuming that the blackholes were created in the initial stages in the formation of the universe.

17. Feb 24, 2010

### Chalnoth

Well, they would behave much like dark matter, but there's the problem that there's really no way there could be so many that they would vastly outnumber the normal matter. We should also be able to detect them evaporating, which we haven't yet.

18. Feb 24, 2010

### Haelfix

Its not quite that simple, there are many papers on TeV scale blackholes in colliders and collisions scattered around hep-ph or hep-th. It is in principle possible, particularly in the context of extra dimension models and so forth. You would see a rather spectacular display of Kaluza-Klein modes.

Whats impossible is for such objects to exist and simultaneously avoid evaporation, since its the very same semiclassical analysis that predicts their existence that also leads directly to Hawking radiation.

19. Feb 24, 2010

### Ich

That's interesting.
I've been discussing with an LHC-critic (maybe you know him , O.E. Rössler, who denies the existence of Hawking radiation) two years ago, and just a few weeks ago he contacted me again.
Since my QM is rather ...limited, I'd appreciate if you could point me to some basic papers on the connection between creation and evaporation.

20. Feb 24, 2010

### twofish-quant

In particular, if black holes didn't radiate energy, this would imply that they would have no temperature. If they had no temperature they would have no entropy. If they had no entropy then you could toss stuff into it, and the entropy of the universe would decrease. If that happened, you'd violate the second law of thermodynamics.

21. Mar 2, 2010

I agree:)