a black hole conspiracy
it has been known for a number of years that there is a curious set of correlations between the central supermassive black holes in galaxies and the global properties of the galaxies
in particular, the inferred mass of the central black hole correlates quite well with the mass of the spheroidal component of the host galaxy (but not the disk mass, so the correlation with the galaxy mass as a whole is not there), and, there is an even better correlation with the "characteristic velocity" of the stars in the galaxy at some fairly large radius (how to define that consistently is still debated, but the correlation is there). note that there are some observational biases in these measurements, in particular it is hard to see "undermassive" black holes in high mass halos, so there could be hidden data points "below the line"
there are supermassive black in almost all galaxies, we think at least 85% of respectably massive galaxies have central supermassive black holes, and possibly all of them do, for a generous definition of "supermassive" (some of the black holes could be down at few thousands or tens of thousands of solar masses)
the black holes can and do accrete, in the process radiating very strongly
it is thought that a typical supermassive black hole may roughly double its mass through gas accretion, over a period of tens of millions of years (this is hard to estimate well - we know the accretion time is not extremely short, on average, since then the observed radiation could not be accounted for, but if the typical accretion time scale is longer, then most of the radiation tends to come out in the last 50 million years or so, so the estimates are biased to push down to order tens of millions of years)
the energy released in the process is adequate to affect the structure of the galaxy, the question is how it does so - coupling the energy to the gas and stars on large scales is hard
first, the accretion disk, and "radius of influence" of the black hole is quite small, light years, or tens of light years, whereas the effects on the galaxy are seen on scales of thousands of light years.
secondly, the accretion disk is thought to be low mass (maybe less than 0.1% of the black hole mass at any given time) and has short characteristic time scales (tens of thousands of years). this means the disk must be replenished from gas further out many times - thousands of times - so we expect the accretion to be episodic, not continuos - it is low duty cycle accretion
the stuff further out moves on orbital time scales of tens of millions or hundreds of millions of years, to affect the global structure of the galaxy, the black hole accretion must lead to gas being moved around and star formation to be directly affected by the accretion
this is a puzzle - the radiation field by itself does not seem adequate, a more efficient way to do this would be to mechanically couple the black hole accretion energy to the gas - this can be done if about half the gas flowing in can be pushed back out at relativistic speeds - we do see jets from some black holes, and the termination shocks of the jets show evidence for prolonged energy deposition and very large amounts of energy deposited - equivalent to the rest mass energy of millions of solar masses
but, if we see the energy break out to large scales, it is not being deposited within the galaxy with any efficiency, and these are collimated flows - how are they affecting the global structure of the galaxy
this is probably a "messy physics" problem - needing more high resolution understanding of the microphysics and the coupling of the physics on different scales
it is very important, since stars are in galaxies, and planets of some interest orbit around stars, so it would be good to know how the central black holes are affecting star formation on global scales, as it seems they do
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it is very important, since stars are in galaxies, and planets of some interest orbit around stars, so it would be good to know how the central black holes are affecting star formation on global scales, as it seems they do
Did you just tie MBHs to astrobiology? Good work! Maybe the next talk I give will have a plot with N_planets on the y-axis and BH mass on the x-axis.
darn' tootin' I did.
Tell me the slope, or even the sign of the slope, and I'll be interested!
It has to be positive. I'll go out on a limb and say the slope is 1 for number of planets in the galaxy bulge.
Since log(M_BH) ~ log(L_bulge), that means that log(M_BH) ~ log(N_stars_b), from which we can conclude that log(M_BH) ~ log(N_planets_bulge). This ignores any metallicity dependence, but my guess is that the variance of metallicities in bulges isn't enough to overcome the effect from the shear number of stars.
(1) Supermassive black holes tied to astrobiology? Of course! See Prof. Gregory Benford's Galactic Center Saga:
1. In the Ocean of Night (1976, Dial Press)
2. Across the Sea of Suns (January 1984, Simon & Schuster, ISBN 978-0-671-44668-0)
3. Great Sky River (December 1987, Bantam Books, ISBN 978-0-553-05238-1)
4. Tides of Light (January 1989, Bantam Books, ISBN 978-0-553-05322-7)
5. Furious Gulf (July 1994, Bantam Spectra, ISBN 978-0-553-09661-3)
6. Sailing Bright Eternity (August 1995, Bantam Spectra, ISBN 978-0-553-08655-3)
[By the way, those novels have many poetic sentences and lengthy paragraphs of mine which Greg intentionally quoted from: Jonathan Vos Post, "Human Destiny and the End of Time" {Quantum, No.39, Winter 1991/1992, Thrust Publications, 8217 Langport Terrace, Gaithersburg, MD 20877; ISSN 0198-6686}
in which I gave the first published explanation of why we are almost certainly simulated by a civilization about a googol years in the future, composed of extremely dilute electron-positron ambiplasma (itself based on discussions that I had with Freeman Dyson and Richard Feynman who died exactly 20 years ago yesterday)].
Years after my influential Quantum article, philosopher Nick Bostrom published a degraded version of my prior-published notion, got tremendous publicity from New Scientist and the New York Times and the like, in part because he is orbited by an accretion disks of cult follower who, by the way, insist in writing that I don't exist, but am merely a "alibi" of famed internet pioneer John Sokol and wdely published and respected professor Philip V. Fellman [Southern New Hampshire University], both of whom requested that the defamations be removed from the Bostrom cultists' web sites, but they refuse on the grounds that we don't exist, which is much more Philip K. Dickish than Greg Benfordian.
(2) "shear number of stars" should be "sheer number of stars" unless they are being ergodically mixed.
See also:
Jonathan Vos Post, "Star Power for Supersocieties" [Omni, ed. Ben Bova and Robert Sheckley, Apr 1980] ISSN-0149-8711, $2.00
* 1st popular article to predict giant black hole in the center of Milky Way galaxy;
* 1st popular discussion of J. Post invention "gravity wave telegraph" which may be the way that ETs are finally detected by LIGO or LISA.
I suppose it shows that, while I was an Adjunct Professor of Astronomy at Cypress College, reporting to the Chairman of Physics and Astronomy who got his PhD from Greg Benford (who recommended me for the job, as did Physicist/sometimes Astronmer Caltech VP/Provost Steve Koonin), I never had my contract extended to full-time Tenure Track, because the "Equivalence Committee" of bureaucrats decided that if I had at leasr 210 publications, presentations, and broadcasts about Astronomy and the Space program some of them Science Fiction with the likes of my coauthors Asimov, Bradbury, Clarke, and Heinlein, then I must be far too busy writing to have enough time for teaching students. Caltech never prepared me for 2nd rate schools, but that's another story.
Thanks again for the liveblogging, which is extremely exciting and well done!