A Universe of Black Holes: I

Visiting lovely KITP for the A Universe of Black Holes programme, and specifically the associated "Massive Black Holes: Birth, Growth and Impact" workshop.

As usual the talks will (eventually) be posted on line, both slides and web, but in the mean time I will be semi-transcribing my semi-coherent stream-of-consciousness thoughts on the issues.

And we are off, with new KITP Director Lars Bildsten welcoming the hordes.
As is typical, about half the attendees are noobs and have not visited KITP before.
Are they in for a treat.

Marta Volonteri (IAP), one of the workshop organizers, leads off with an overview of science targets - BH formation channels, including observational consequences; BH accretion and feedback; nice sim from Y. Dubois shown of AGN UV contribution at high-z; and, BH mergers and gravitational radiation, as well as EM counterparts.

and we start with first invited talk: Priya Natarajan (Yale) on "Sowing Seeds: assembling the first black holes in the early Universe" - looking at formation and growth of supermassive black holes during structure formation in the (very) early universe.

Issues: growth channels; seed formation; light vs massive seeds; growth, mergers, interaction and feedback to structure formation - start with ΛCDM, natch.
i) baryonic gas accretion - thin disk accretion is radiately efficient ~ 0.1 mc² vs radiatively inefficient accretion - efficiency drops by ~ 6 (+/-) orders of magnitude at slightly lower (mass accretion rate)/(Eddington rate) - observational bias, fraction of SMBH in each mode redshift dependent.
How do we get to M_galaxy-M_{black hole} relation, much less the M_{black hole}-σ relation, and how do they vary with z?

eg. does M-M relation flatten or turnover at low masses;
wtf is going on with the ultra-massive black holes (and why did nobody believe us when we pointed out the must be there over a decade ago...)

very nice update of te 1975 Martin Rees "all ways to make SMBH seeds" chart - must swipe for classes/talks!

Strong assertion that the pop III stars don't form as single massive (over 100 solar mass stars) but that new sims show small clusters of smaller (10-50 solar mass) stars - get cluster of small BH at high z - should be hearing a lot more about this during the week.

Massive "quasi-star" seeds back - critical that "star" forming from gas clouds >> 1,000 solar masses never approaches equilibrium (or it blows itself apart [ed]) - so dynamic growth collapsing directly to 1,000-1,000,000 solar mass SMBH.
Need very efficient internal angular momentum transport.
Tricky.
Messy.
Basic idea been around for a long time, details still a bit vague despite attempts of many generations of brave smart PhDs and proto-PhDs.

Good test is what galaxies don't have central super-massive black holes - corollary: this shows up in the merger dynamics; grav rad signature; confounded by possibility of grav rad recoil removing SMBH from galaxies - just need statistics of SMBH binaries and mass function as function of redshift.

Nice call out to Matt Turk and Britton Smith sims.

Also occupation fraction of low mass SMBH in low mass galaxies ought to be a strong test of SMBH formation channels.

Gastrodynamics are messy.

Summary: many models need epochs of super-Eddington accretion; need worryingly long durations of efficient near Eddington accretion - not really consistent with obs (though there is an interesting bias on estimators of duration of radiatively efficient accretion) - notes Mayer et al's work on late direct collapse to SMBH during mergers.

Q&A:
Q:Krolik - why do some galaxies (maybe) do direct collapse
A: angular momentum must be a parameter, but sims show global spin parameter is poor proxy, depends on mean ang mom in core, which is (presumably) dominated by local torque history, not initial λ - well, there goes another nice oversimplified idea
Turbulence invoked, PLEASE DON'T MENTION MAGNETIC FIELDS,
yet.

Followed by Silvia Bonoli on sims with Mayer.

Back from coffee: "observational constraints"?
This is a Theory Institute dammit!
We don't need no steenkin' observational constraints!

Ok, maybe too much coffee...

So, we learn that after 4 decades, people are still ignoring tests of what numerical resolution is needed to resolve some physical processes.
Sigh.

Momentum conservation matters, and numerical noise is a killer.
Oh, and cuspy halos drive divergent random walks - first pointed out by Quinlan 20 years ago.