Supermassive BH feeding on Dark matter

[Dmitry67]

I know that typical Black Holes don't feed on Dark matter because they are tiny, so the direct hit is unlikely. While normal matter has friction and can slow down close to the BH, Dark matter just pass it by.

What's about supermassive (>10^10 solar masses) black holes?
Do they consume significant amounts of the dark matter? Radius of the event horizon is proportional to the mass, and the probability of the 'direct hit' - is M squared. Supermassive BH can consume up to 10^20 times more Dark matter than Sun. Even more, supermassive BH usually resides in the center of galaxies, and that position favours the consumpiton of DM.

 

[phinds]

Doesn't sound right to me. Gravitationally, there is no difference between regular matter and dark matter. Massive amounts of regular matter falling into a black hole might have a slight difference because of internal collisions but other than that the two should be the same.

 

[Chalnoth]

I know that typical Black Holes don't feed on Dark matter because they are tiny, so the direct hit is unlikely. While normal matter has friction and can slow down close to the BH, Dark matter just pass it by.

What's about supermassive (>10^10 solar masses) black holes?
Do they consume significant amounts of the dark matter? Radius of the event horizon is proportional to the mass, and the probability of the 'direct hit' - is M squared. Supermassive BH can consume up to 10^20 times more Dark matter than Sun. Even more, supermassive BH usually resides in the center of galaxies, and that position favours the consumpiton of DM.

There may be some impact of dark matter on black hole growth. But I strongly suspect it isn't all that significant. If it were, then there wouldn't be such a tremendous variation in the masses of the supermassive black holes at the centers of galaxies.

 

[phinds]

There may be some impact of dark matter on black hole growth. But I strongly suspect it isn't all that significant. If it were, then there wouldn't be such a tremendous variation in the masses of the supermassive black holes at the centers of galaxies.

Hm ... I don't follow that. Could you expand on it a bit?

 

[Chalnoth]

Hm ... I don't follow that. Could you expand on it a bit?

The amount of dark matter in a galaxy varies far less than the amount of baryonic matter.

 

[phinds]

The amount of dark matter in a galaxy varies far less than the amount of baryonic matter.

DOH ! ... I knew that, just wasn't connecting the dots. Thanks.

Do we know if the dark matter was as uniformly distributed as the galaxies were forming as it appears to be now?

 

[Chalnoth]

DOH ! ... I knew that, just wasn't connecting the dots. Thanks.

Do we know if the dark matter was as uniformly distributed as the galaxies were forming as it appears to be now?

Well, in general you end up with massive differences in baryonic densities the moment stars start to turn on, because stars tend to blow matter out of lighter galaxies. It is this, I think that drives the vastly different ratios of baryonic matter to dark matter that we see in various galaxies. If it weren't for this sort of feedback, I think we'd expect all galaxies to simply track the average baryon/dark matter ratio we observe in the CMB.

This is the point, I think: it's not so much that dark matter doesn't vary, but instead that baryonic physics tends to dramatically alter the ratio of baryonic matter to dark matter.

So in the end, I think we can trace the majority of the variation in the ratio supermassive black hole mass to halo mass to be due to the baryonic content.

 

[theon]

I recently gave an explanation in arXiv:1108.1697: "Model for common growth of supermassive black holes, bulges and globular star clusters: ripping off Jeans clusters". The BHs are fed by dark MACHOs (small Jupiters), that is: baryonic dark matter (missing baryons). This mechanism stems with Carlos Frenk's great insight (known to several others since 15 years) that the standard theory of Cold Dark Matter would be wrong.

 

[Chalnoth]

I recently gave an explanation in arXiv:1108.1697: "Model for common growth of supermassive black holes, bulges and globular star clusters: ripping off Jeans clusters". The BHs are fed by dark MACHOs (small Jupiters), that is: baryonic dark matter (missing baryons). This mechanism stems with Carlos Frenk's great insight (known to several others since 15 years) that the standard theory of Cold Dark Matter would be wrong.

MACHO's don't make up a significant fraction of the missing baryons. The vast majority of the baryonic matter remains as gas.