Clustering of primordial black holes

[wolram]

http://arxiv.org/abs/astro-ph/0509141

Clustering of Primordial Black Holes: Basic Results
Authors: James R. Chisholm
Comments: 22 pages, 3 figures; submitted to PRD

We investigate the spatial clustering properties of primordial black holes (PBHs). With minimal assumptions, we show that PBHs are created highly clustered. They constitute an isocurvature perturbation that is non-linear upon horizon entry. Using the peaks theory model of bias, we compute the PBH two-point correlation function and power spectrum. A consequence of this is that PBHs cannot serve as the majority of dark matter in the universe. We show that this clustering could lead to PBH mergers that spoil the mass-creation time relation.

 

[vincentm]

uhm, what is the difference between a PBH and a regular BH? Or are they the same thing? We know that with galactic mergers black holes can grow. However i don't know of anyother way they can increase in mass.

 

[SpaceTiger]

uhm, what is the difference between a PBH and a regular BH?

A PBH is just a "primordial black hole", meaning that it formed in the early moments of the universe. This would be in contrast to, for example, a black hole that formed from a collapsed star.

We know that with galactic mergers black holes can grow. However i don't know of anyother way they can increase in mass.

Black holes can grow by accreting material around them, merging into one another, or disrupting nearby objects, like stars. There are also more exotic proposals that involve them swallowing dark energy, but that's still just an idea.

 

[vincentm]

A PBH is just a "primordial black hole", meaning that it formed in the early moments of the universe. This would be in contrast to, for example, a black hole that formed from a collapsed star.

Okay, that's what i was thinking, upon posting that question i had forgotten the meaning of the word "primordial" and it's application, thanks

Black holes can grow by accreting material around them,

Well aren't they considered messy eaters meaning they consume more than they can chew, hence the reason for the acretion disks that are formed? but say for instance that one is formed in a binary system in which one of the 2 stars collapses, and acretes matter from the other stars, and after which there is no other matter to consume, will it just die out?

merging into one another,

This i have read and that makes sense to me, they become super massive black holes?

or disrupting nearby objects, like stars.

I apologize, but on this, can you elaborate?

There are also more exotic proposals that involve them swallowing dark energy, but that's still just an idea.

this i haven't heard of, yet </hint>

 

[SpaceTiger]

Well aren't they considered messy eaters meaning they consume more than they can chew, hence the reason for the acretion disks that are formed?

Accretion disks form primarily because of the conservation of angular momentum. A black hole cannot simply "pull in" a clump of gas if that gas is moving perpendicular to the line between it and the black hole. Instead of fall in, the gas will tend to orbit around it, much like the planets orbit the sun. However, angular momentum can be transported from one object to another, so if that gas can give its angular momentum away to some other object (usually more gas), then it can fall in closer to the black hole. The exact mechanism by which the angular momentum is exchanged is still a matter of debate, but most astronomers think it has to do with magnetic fields.

but say for instance that one is formed in a binary system in which one of the 2 stars collapses, and acretes matter from the other stars, and after which there is no other matter to consume, will it just die out?

Eventually, but not for a very long time. Black holes evaporate by way of Hawking radiation.

This i have read and that makes sense to me, they become super massive black holes?

The distinction between stellar mass black holes, supermassive black holes, and intermediate mass black holes is pretty arbitrary. I would say that a stellar mass black hole is one with less than about 100 solar masses and a supermassive black hole would be one with more than about a million solar masses.

I apologize, but on this, can you elaborate?

Because of their strong gravity, black holes can induce large tidal forces on nearby objects. If it's close enough to the black hole, a star can be tidally disrupted (torn asunder) and "swallowed" by the black hole.

this i haven't heard of, yet

We're still not sure what "dark energy" is, but in some theories (like quintessence), it could be due to some scalar field. This would mean that the dark energy could be accreted by the black hole. Here's one such reference that discusses this issue:

Bean & Magueijo 2002

 

[Garth]

The other difference between PBHs and other sorts of BH is they can be of small, even very small, mass. This is because they were created out of small pockets of overdensity in the very early universe when gravitational forces were huge, because densities were huge.

Those of a mass equal to Mount Everest would be evaporating by Hawking radiation about now... (GRBs?)

Small PBHs were once thought to be a candidate for a DM particle, but I think that has been ruled out now (?).

Garth

 

[SpaceTiger]

Small PBHs were once thought to be a candidate for a DM particle, but I think that has been ruled out now (?).

Some would say so, but it's not quite clear. There are direct observational constraints on massive PBHs, but the smaller ones are considerably more elusive. They can't be constrained directly, but some claim that their presence would cause problems for reionization.

 

[Chronos]

There are also constraints on the abundance of miniature PBH's based on the cosmic gamma ray background.