GROWING BLACK HOLES

1. GROWING BLACK HOLES Mitch Begelman JILA, University of Colorado

2. COLLABORATORS • Marta Volonteri (Michigan) • Martin Rees (Cambridge) • Elena Rossi (JILA/Leiden) • Phil Armitage (JILA) • Isaac Shlosman (JILA/Kentucky) • Kris Beckwith (JILA) • Jake Simon (JILA)

3. BLACK HOLES FORMED… EARLY QSOs with M>109M at z>6 OFTEN One per present-day galaxy

4. HOW DID THESE BLACK HOLES GET THEIR START?

5. 2 SCHOOLS OF THOUGHT: • Pop III remnants • Stars form, evolve and collapse • M*~103 M • MBH~102 M • Direct collapse • Massive gas cloud accumulates in nucleus • Supermassive star forms but never fully relaxes; keeps growing until collapse • M*>106 M • MBH >104 M

6. Rees’s flow chart Rees, Physica Scripta, 1978

7. 32 years later … Begelman & Rees, “Gravity’s Fatal Attraction” 2nd Edition, 2010

8. Keeping up with the times… Begelman & Rees, “Gravity’s Fatal Attraction” 3nd Edition E-book?

9. TRADEOFFS: Smaller seeds, more growth time • Pop III remnants • ~100 (?) M BHs form at z > 20 • 105-6 M halos, Tvir ~ 102-3 K • Grow by mergers & accretion • Problems: • Slingshot ejection from merged minihalos? • Feedback/environment inhibits accretion? • Direct collapse • Initial BH mass = ? at z < 12 • 108-9 M halos, Tvir >104 K • Grow mainly by accretion • Problem: • Fragmentation of infalling gas? Larger seeds, less growth time

10. STAGE I: COLLECTING THE GAS The problem: angular momentum The solution: self-gravitating collapse

11. SELF-GRAVITATING COLLAPSE: A GENERIC MECHANISM: • “Normal” star formation • Pop III remnants • Direct collapse

12. Gas collapses if DM gas gas Halo with slight rotation DM “BARS WITHIN BARS” Dynamical loss of angular momentum through nested global gravitational instabilities Shlosman, Frank & Begelman 1989

13. Collapsing gas in a pre-galactic halo: R-2 density profile Wise, Turk, & Abel 2008

14. Instability at distinct scales → nested bars Global instability, “Bars within Bars”: Wise, Turk, & Abel 2008

15. WHY DOESN’T THE COLLAPSING GAS FRAGMENT INTO STARS? IT’S COLD ENOUGH … … BUT IT’S ALSO HIGHLY TURBULENT

16. Collapse generates supersonic turbulence, which inhibits fragmentation: Wise, Turk, & Abel 2008

17. HOW TURBULENCE COULD SUPPRESS FRAGMENTATION BAR THE KEY IS DISK THICKENING Razor-thin disk (Toomre approximation): FRAGMENTATION SETS IN BEFORE BAR INSTABILITY FRAGMENTS ⇦FRAGMENT SIZE ROTATIONAL SUPPORT ⇨ Begelman & Shlosman 2009

18. HOW TURBULENCE COULD SUPPRESS FRAGMENTATION BAR THE KEY IS DISK THICKENING Disk thickened by turbulent pressure: BAR INSTABILITY SETS IN BEFORE FRAGMENTATION FRAGMENTS ⇦FRAGMENT SIZE WHY? THICKER DISK HAS “SOFTER” SELF-GRAVITY ⇨ LESS TENDENCY TO FRAGMENT (DOESN’T AFFECT BAR FORMATION) ROTATIONAL SUPPORT ⇨ Begelman & Shlosman 2009

19. HOW TURBULENCE COULD SUPPRESS FRAGMENTATION BAR THE EFFECT IS DRAMATIC 5% of turbulent pressure used for thickening : ENOUGH TO KILL OFF FRAGMENTATION FRAGMENTS ⇦FRAGMENT SIZE MORE SIMULATIONS (WITH HIGHER RESOLUTION) NEEDED! ROTATIONAL SUPPORT ⇨ Begelman & Shlosman 2009

20. Rapid infall can’t create a black hole directly… At radiation trapped in infalling gas halts the collapse

21. STAGE II: SUPERMASSIVE STAR

22. SUPERMASSIVE STARS Hoyle & Fowler 1963 • Proposed as energy source for RGs, QSOs • Burn H for ~106 yr • Supported by radiation pressure fragile • Small Pgstabilizes against GR to 106 M • Small rotation stabilizes to 108-109 M

23. THINGS HOYLE & FOWLER DIDN’T KNOW ABOUT SUPERMASSIVE STARS … because they didn’t worry about how they formed • They are not thermally relaxed

24. INCOMPLETE THERMAL RELAXATION SWELLS THE STAR:

25. THINGS HOYLE & FOWLER DIDN’T KNOW ABOUT SUPERMASSIVE STARS … because they didn’t worry about how they formed • They are not thermally relaxed • They are not fully convective

26. Scaled radius STRUCTURE OF A SUPERMASSIVE STAR CONVECTIVE CORE matched to RADIATIVE ENVELOPE POLYTROPE “HYLOTROPE” • (hyle, “matter” + tropos, “turn”) Thanks, G. Lodato & A. Accardi!

27. HYLOTROPE, NOT HELIOTROPE!!

28. FULLY CONVECTIVE PARTLY CONVECTIVE INCOMPLETE CONVECTION DECREASES ITS LIFE & MAX. MASS MAX. MASS

29. THINGS HOYLE & FOWLER DIDN’T KNOW ABOUT SUPERMASSIVE STARS … because they didn’t worry about how they formed • They are not thermally relaxed • They are not fully convective • If made out of pure Pop III material they quickly create enough C to trigger CNO

30. METAL-POOR STARS BURN HOTTER

31. A BLACK HOLE FORMS SMALL (< 103 M) AT FIRST … … BUT SOON TO GROW RAPIDLY

32. STAGE III: QUASISTAR

33. “QUASISTAR” • Black hole accretes from envelope, releasing energy • Envelope absorbs energy and expands • Accretion rate decreases until energy output = Eddington limit – supports the “star” Begelman, Rossi & Armitage 2008

34. SO THE BLACK HOLE GROWS AT THE EDDINGTON LIMIT, RIGHT?

35. BUT WHOSE LIMIT? EDDINGTON

36. GROWTH AT EDDINGTON LIMIT FOR ENVELOPE MASS > 103-4 X BH MASS EXTREMELY RAPID GROWTH

37. Radius ~ 100 AU Central temp. ~106 K Tphot drops as BH grows “QUASISTAR” • Resembles a red giant • Radiation-supported convective envelope • Photospheric temperature drops as black hole grows

38. DEMISE OF A QUASISTAR • Critical ratio:RM=(Envelope mass)/(BH mass) • RM < 10: “opacity crisis” (Hayashi track) • RM < 100: powerful winds, difficulty matching accretion to envelope (details very uncertain) Final black hole mass:

39. STAGE IV: “BARE” BLACK HOLE “Normal” growth via accretion & mergers

40. THE COSMIC CONTEXT • Collapse occurs only in gas-rich & low ang. mom. halos • Need ang. mom. parameterλ~0.01-0.02 vs. meanλ~0.03-0.04 • Competition with Pop III seeds • Pre-existing Pop III remnants may inhibit quasistar formation • ... but pre-existing quasistars can swallow Pop III remnants • Merger-tree models vs. observational constraints: • Number density of BHs vs. z (active vs. inactive) • Mass density of BHs vs. z (active vs. inactive) • BH mass function vs. z • Total AGN light (Soltan constraint) • Reionization Volonteri & Begelman 2010

41. TOTAL AGN LIGHT BLACK HOLE mass density POP III ONLY All BHs: (thin lines) Active BHs: (thick lines) Volonteri & Begelman 2010

42. CAN SUPERMASSIVE STARS OR QUASISTARS BE DETECTED? Supermassive stars: …strong UV source (hard to distinguish from clusters of hot stars) Quasistars peak in optical/IR: some hope?

43. 1/JWST field 1/JWST field JWST quasistar counts Tphot=4000 K Band: 2-10 m Sens. 10 nJy λspin<0.02 Lifetime ~106 yr λspin<0.01

44. WHAT ABOUT M-σ? • Do AGN outflows really clear out entire galaxies? – or is global feedback a “red herring”? • Do BH grow mainly as Eddington-limited AGN or in smothered, “force-fed” states (e.g., following mergers) • if the latter, then BH growth could be coupled to σthrough infall rate σ3/G • ... but what is the regulation mechanism?

45. To conclude … BOTH ROUTES TO SUPERMASSIVE BLACK HOLE FORMATION ARE STILL IN PLAY MASSIVE BLACK HOLE FORMATION BY DIRECT COLLAPSE LOOKS PROMISING THE PROCESS INVOLVES 2 NEW CLASSES OF OBJECTS QUASISTARS AT Z~6-10 MIGHT BE DETECTABLE WITH JWST • Many unsolved problems: Effects of mass loss? Late formation after mergers? Formation around existing black holes? .... • Supermassive stars ⇨ initial seeds • Quasistars ⇨ rapid growth in massive cocoon Requires self-gravitating infall without excessive fragmentation

46. DIRECT COLLAPSE LOOKS PROMISING CORE COLLAPSE OF SUPERMASSIVE STARS RAPID GROWTH INSIDE MASSIVE COCOONS QUASISTARS DETECTABLE?