GROWING BLACK HOLES

Mitch Begelman

JILA, University of Colorado

GROWING BLACK HOLES

COLLABORATORS

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

EARLYQSOs with M>109M at z>6

OFTENOne per present-day galaxy

BLACK HOLES FORMED…

HOW DID THESE BLACK HOLES GET

THEIR START?

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

Rees, Physica Scripta, 1978

Rees’s flow chart

32 years later …

Begelman & Rees, “Gravity’s Fatal Attraction” 2nd Edition, 2010

Begelman & Rees, “Gravity’s Fatal Attraction” 3nd Edition E-book?

Keeping up with the times…

• 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?

~ Smaller seeds, more growth time

Larger seeds, less growth time

TRADEOFFS:

STAGE I:

COLLECTING THE GAS

The problem: angular momentum

The solution: self-gravitating collapse

SELF-GRAVITATING COLLAPSE: A GENERIC MECHANISM:

• “Normal” star formation

• Pop III remnants

• Direct collapse-1

Sun4 yr M2.0 K,10 MT

G

T

G

vM

2/33

~

-1Sun

24 yr M1010~ K,1000100~ MT

-1Sun

45 yr M1010~ K,10010~ MT

DM

gas

DM

gas

(approx.) 25.0en. pot.

en. rot.

Halo with slight rotation Gas collapses if virialgas TT

“BARS

WITHIN

BARS”

Shlosman, Frank & Begelman 1989

Dynamical loss of angular momentum

through nested global gravitational instabilities

Wise, Turk, & Abel 2008

Collapsing gas in a pre-galactic halo:

R-2 density profile


Global instability, “Bars within Bars”:

Instability at distinct scales → nested bars

WHY DOESN’T THE COLLAPSING GAS FRAGMENT

INTO STARS?

IT’S COLD ENOUGH …

… BUT IT’S ALSO HIGHLY TURBULENT


Collapse generates supersonic turbulence, which inhibits fragmentation:

HOW TURBULENCE COULD SUPPRESS FRAGMENTATION

Begelman & Shlosman 2009

Razor-thin disk (Toomre approximation):

FRAGMENTATION SETS IN BEFORE BAR INSTABILITY

ROTATIONAL SUPPORT ⇨

⇦ F

RA

GM

EN

T S

IZE

THE KEY IS DISK THICKENING

BAR

FR

AG

ME

NT

S

kGkvt 22222



Disk thickened by turbulent pressure:

BAR INSTABILITY SETS IN BEFORE FRAGMENTATION


⇦ F

RA

GM

EN

T S

IZE

THE KEY IS DISK THICKENING

BAR

FR

AG

ME

NT

S

WHY?

THICKER DISK HAS “SOFTER” SELF-GRAVITY

⇨ LESS TENDENCY TO FRAGMENT

(DOESN’T AFFECT BAR FORMATION)hk

kGkvt

1

22222



5% of turbulent pressure used for thickening :

ENOUGH TO KILL OFF FRAGMENTATION


⇦ F

RA

GM

EN

T S

IZE

THE EFFECT IS DRAMATIC

BAR

FR

AG

ME

NT

S

MORE SIMULATIONS (WITH HIGHER RESOLUTION) NEEDED!

At

radiation trapped in infalling gas halts the collapse

Rapid infall can’t create a black hole directly…

AUyr 1

4~1-

SolM

MR

STAGE II:

SUPERMASSIVE STAR

SUPERMASSIVE

STARS

• Proposed as energy source for RGs, QSOs • Burn H for ~106 yr• Supported by radiation pressure fragile

• Small Pg stabilizes against GR to 106 M

• Small rotation stabilizes to 108-109 M

Hoyle & Fowler 1963

THINGS HOYLE & FOWLER DIDN’T KNOW

ABOUT SUPERMASSIVE STARS

• They are not thermally relaxed

… because they didn’t worry about how they formed

AU 4~ mR

INCOMPLETE THERMAL RELAXATION SWELLS THE STAR:

MR



• They are not thermally relaxed • They are not fully convective


STRUCTURE OF A SUPERMASSIVE STAR

CONVECTIVE CORE

matched to

RADIATIVE ENVELOPE

0 1 2 3 4 5 6 70 .0

0 .2

0 .4

0 .6

0 .8

1 .0

cT

T

Scaled radius

coreM

M*

const.3/4 P

POLYTROPE

)(3/23/4 rMP

“HYLOTROPE”

Thanks, G. Lodato & A. Accardi!

(hyle, “matter” + tropos, “turn”)

HYLOTROPE,

NOT

HELIOTROPE!!

FULLY CONVECTIVE

PARTLY CONVECTIVE

MAX. M

ASS

INCOMPLETE CONVECTION DECREASES ITS LIFE & MAX. MASS



• 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


METAL-POOR STARS BURN HOTTER

A BLACK HOLE FORMS

SMALL (< 103 M) AT FIRST …

… BUT SOON TO GROW RAPIDLY

STAGE III:

QUASISTAR

“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

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

BUT WHOSE LIMIT?

EDDINGTON

GROWTH AT EDDINGTON LIMIT FOR ENVELOPE MASS > 103-4 X BH MASS

EXTREMELY RAPID GROWTH

“QUASISTAR”

• Resembles a red giant • Radiation-supported convective envelope • Photospheric temperature drops as black hole

grows

Central temp. ~106 K

Radius ~ 100 AU

Tphot drops as BH grows

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:

Sol

SolSol

MBH

M

MM

MRM

64

1-27

1010~

yr 110~

STAGE IV:

“BARE” BLACK HOLE

“Normal” growth via accretion & mergers

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

BLACK HOLE mass density

All BHs: (thin lines) Active BHs: (thick lines)

TOTAL AGN LIGHT POP III

ONLY

Volonteri & Begelman 2010

CAN SUPERMASSIVE STARS OR QUASISTARS BE DETECTED?

Quasistars peak in optical/IR: some hope?

Supermassive stars:

AGNmodest a to...similar K102~

erg/s104~4/15

eff

45

mT

L

…strong UV source (hard to distinguish from clusters of hot stars)

JWST quasistar counts

Tphot=4000 K Band: 2-10 mSens. 10 nJy

Lifetime ~106 yr

λspin<0.02

λspin<0.01

1/JWST field

1/JWST field

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?

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

Requires self-gravitating infall without excessive fragmentation

Supermassive stars initial ⇨seedsQuasistars ⇨ rapid growth in massive cocoon

Many unsolved problems: Effects of mass loss? Late formation after mergers? Formation around existing black holes? ....

DIRECT COLLAPSE LOOKS PROMISING

CORE COLLAPSE OF SUPERMASSIVE STARS

QUASISTARS DETECTABLE?

RAPID GROWTH INSIDE MASSIVE COCOONS

GROWING BLACK HOLES

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