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Theoretical ideas for the formation and feeding of IMBHs

Cole MillerUniversity of Maryland and Joint

Space-Science Institute

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Outline Formation and challenges

Early starsDynamics: young massive clustersDynamics: black hole mergers

FeedingStars: massive or giantsTemporary, from molecular cloudOther?

I will provide far more questions than answers!

Formation of IMBHs

Problem: ~103 Msun too much for normal star!

Population III stars Low Z; weak winds

Collisions or mergers Needs dense clusters Young: collisions Old: three-body

http://www.npaci.edu/enVision/v17.4/images/star2.gif

Are Early Stars Actually Large?

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Sta

cy &

Bro

mm

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More recent high-resolution work has shown that primordialgas might fragment into 10s of Msun stars, not 100s.On the other hand, stars with MZAMS>200 Msun are seenin the LMC (Crowther et al. 2010); might they produce MBH>100 Msun (Belczynski et al. 2014)?

Cluster Thermodynamics Close analogy with

thermo! Equipartition of energy

=> heavy things sinkMass seg seen in GC (e.g., Sosin 1997)

Increase of entropy => with time core gets denser, outside expands

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3-body interactions Binary-single interactions

harden hard binaries, soften soft binaries

Soft binaries are eventually “ionized”: they separate

But recoil from 3-body interactions with hard binaries supplies energy to cluster, holds off core collapse if there is enough energy in the binaries

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Formation of IMBHs Problem: ~103 Msun too

much for normal star! Population III stars

Low Z; weak winds Collisions or mergers

Needs dense clusters Young: collisions Old: three-body

Gurkan et al. 2006

Problems With Winds?

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Glebbeek et al. 2009

Suggested that winds might blow away more mass than is added in runaway collisions

Does this prevent the formation of ultramassive stars?

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Not Necessarily

As Melvyn Davies has pointed out, collisions happen faster than Kelvin-Helmholtz time

Thus stars don’t relax; they are a bag of cores

Far from clear that winds will resemble those of a star of the same mass

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Not necessarily, pt 2 Multiple M>150

Msun stars seen in R136

LMC metallicity is ~40% of solar, so don’t need Z<<1

Wind losses apparently not catastrophic

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Crowther et al. 2010

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Formation of IMBHs Problem: ~103 Msun too

much for normal star! Population III stars

Low Z; weak winds Collisions or mergers

Needs dense clusters Young: collisions Old: three-body

From Steinn Sigurdsson

Problems With Ejection? Maybe...

Early calculations assumed that in GC size clusters, stellar-mass BHs would quickly form a dense subcluster

Then, they would kick each other out via three-body interactions

Few mergers; if they did merge, GW recoil would certainly kick them out

Few options for growth04/19/2023 12

...But Maybe Not More recent sims

show that BHs do not form dense subcluster (also Trenti+van der Marel)

There is thus time to accumulate

GW kicks still bad, but not for BH-star

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Morscher et al. 2013

Long-Term Core Collapse In GC, binaries prevent deep core collapse But in Miller & Davies 2012, ApJ, 755, 81:

If vdisp>~40 km/s, binaries will be destroyed and core collapse will occurThus MBH production seems inevitable in relaxed clusters with at least this vdisp

Consistent with galaxies known without SMBH: NGC 205, 39 km/s; M33, 24 km/s

Might be a way to form IMBHs in sufficiently compact clusters

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Feeding IMBH: RLOF Roche lobe overflow Star needs to be

massive, or a giant, for needed dM/dt

Implies Porb~days to months/years

Implications for line variation studies

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Kalogera et al. 2004

Feeding HLX-1 With Wind? Could a wind power

a ULX? We proposed that a

wind from a recently-stripped RG core could power HLX-1

Maybe easier to explain burst trends

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Miller, Farrell, Maccarone 2014

Tidal Disruptions by IMBHs?

04/19/2023 17Haas et al. 2012

r

T

Tidal Disruptions by IMBHs?

WD disruption suggested as cause of Swift beamed tidal disruption event (Krolik & Piran), some other events

Possible source of gravitational waves, if very close

Not good for persistent fueling of ULXs

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Accretion from Molecular Clouds

Krolik 2004, ApJ, 615, 383 Steady accretion is minimal; luminosity

heats up cloud But an IMBH passing through a MC can

acquire a disk before it lights up Active time few x 105 years, but could

repeat many times Would associate with SF regions

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Conclusions

Without a dynamical mass for ULX primaries, we cannot say for sure whether some or most are powered by IMBHs

Within substantial uncertainties, there do appear to be ways form and power IMBHs

More study is necessary!

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