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Theoretical ideas for the formation and feeding of IMBHs. Cole Miller University of Maryland and Joint Space-Science Institute. Outline. Formation and challenges Early stars Dynamics: young massive clusters Dynamics: black hole mergers - PowerPoint PPT Presentation
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04/19/2023 1
Theoretical ideas for the formation and feeding of IMBHs
Cole MillerUniversity of Maryland and Joint
Space-Science Institute
04/19/2023 2
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
20
13
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
7
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?
8
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?
04/19/2023
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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