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Roeland van der Marel
Intermediate-Mass Intermediate-Mass Black Holes:Black Holes:Formation Formation Mechanisms and Mechanisms and Observational Observational ConstraintsConstraints
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
2
Known Black Holes Known Black Holes (BHs)(BHs)in the Universein the Universe
Stellar mass BHs (3-15 M): Endpoint of the life of massive
stars Observable in X-ray binaries 107-109 in every galaxy
Supermassive BHs (106-109 M): Generate the nuclear activity of
active galaxies and quasars ~1 in every galaxy
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
3
Intermediate-MassIntermediate-MassBlack Holes (IMBHs)Black Holes (IMBHs)
Intermediate mass BHs: Mass range ~ 15 - 106 M
Questions: Is there a reason why they should exist? Is there evidence that they exist?
Status and Progress: These questions can be meaningfully
addressed No consensus yet
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
4
Possible Mechanisms Possible Mechanisms for IMBH Formation for IMBH Formation
Primordial From Population III stars In Dense Star Clusters As part of Supermassive BH
formation
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
5
Primordial Black Hole Primordial Black Hole FormationFormation
BHs may form primordially Requires unusual pressure
conditions (collapse of cosmic strings, spontaneous symmetry breaking, etc.)
Not predicted in standard cosmologies
BH mass horizon mass at formation time: Planck Time (10-43 sec) MBH = Planck Mass (10-5 g) Quark-Hadron phase transition (10-5 sec) MBH = 1 M
1 sec MBH = 105 M
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
6
Primordial Black Holes:Primordial Black Holes:Hawking RadiationHawking Radiation
Primordial BHs withM < 1015 g would have evaporated by now
Hawking radiation is unimportant for BHs of astronomical interest
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
7
Present-Day Evolution Present-Day Evolution of Massive Starsof Massive Stars
Presently the IMF extends to ~200 M
Stars of initial mass 25-200 M shed most of their mass before exploding, yielding BHs with masses MBH ≲ 15 M
Consistent with BH massesdynamically inferred for X-ray binaries
The dozen or so BH candidates inX-ray binaries have masses 3-15 M
Stellar evolution is not presently producing IMBHs
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
8
Population III evolution Population III evolution of Massive Starsof Massive Stars
At zero metallicity: IMF may have been top-heavy Little main-sequence mass loss
Fate of star depends on mass: < 140 M: SN BH or IMBH 140-260 M: e-e+ instability explosion, no
remnant 260 - 105 M: Main Seq no SN IMBH > 105 M: post-Newtonian instability, no Main Seq
IMBH
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
9
Dynamical Evolution of Dynamical Evolution of Star ClustersStar Clusters
Many physical processes in a dense stellar environment can in principle give runaway BH growth
Negative heat capacity of gravity core collapse
Binary heating normally halts core collapse in systems with N* < 106-7
Rees (1984)
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
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A Scenario for IMBH A Scenario for IMBH Formation in Star Formation in Star ClustersClusters
When core collapse sets in, energy equipartition is not maintained the most massive stars sink to the center first
Calculations show that anIMBH can form due torunaway collisions (PortegiesZwart & McMillan) Requires initial Trelax < 25 Myr
or present Trelax < 100 MyrGRAPE 6
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
11
IMBHs and IMBHs and Supermassive Black Supermassive Black Hole FormationHole Formation
Supermassive BH formation: Direct collapse into a BH
Requires that H2 cooling is suppressed Accretion onto a seed IMBH Merging of IMBHs
IMBHs sink to galaxy centers through dynamical friction The galaxies in which IMBHs reside merge hierarchically
Consquences: A substantial population of IMBHs may exist in galaxy halos BHs in some galaxy centers may not have grown
supermassive
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
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How much mass could How much mass could there be in IMBHs?there be in IMBHs?
Supernovae, WMAP, etc: = 1, m = 0.3
Big Bang Nucleosynthesis: b = 0.04
Inventory of luminous material: v = 0.02
Dark matter: Non-baryonic: m - b = 0.26 Baryonic: b - v = 0.02 (IMBHs in Dark Halos?)
Supermassive BHs: SMBH = 10-5.7
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
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Where Could IMBHs be Where Could IMBHs be Hiding?Hiding?
Galaxies Disks/Spheroids/Halos? Galactic nuclei ? Centers of Star Clusters ?
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
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What processes might What processes might reveal IMBHs?reveal IMBHs?
Gravitational lensing brightening / distortion of background objects
Dynamics influence on other objects
Progenitors metals, light, … Accretion X-rays Space-time distortion
Gravitational Waves(LIGO/LISA?)
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
15
Finding Black HolesFinding Black HolesThrough MicrolensingThrough Microlensing
Halo BHs produce microlensing:
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
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Galactic Halo Black Galactic Halo Black Holes:Holes:LMC MicrolensingLMC Microlensing
Microlensing timescale ~ 140 (MBH /M)1/2 days
Observations: efficiency small for timescales of a few years ~1 long-duration event expected for a halo made
of 100 M IMBHs None detected
Conclusion (MACHO team): Galactic Halo not
fully composed of BHs withMBH 1 - 30 M
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
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Dynamical Constraints Dynamical Constraints on IMBHs in Dark Haloson IMBHs in Dark Halos
Are dark halos made entirely of IMBHs? dynamical interactions observational consequences
Limits on viable BH masses: BH accumulation in the galaxy center by dynamical
friction MBH ≲ 106 M (stringent)
disk heating MBH ≲ 106 M (stringent)
heating of small dark-matterdominated systems
MBH ≲ 103-4 M (?) globular cluster disruption
MBH ≲ 103-5 M (?)
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
18
Limits on IMBHs from Limits on IMBHs from Population III starsPopulation III stars
Background Light Limits: All Pop III stars (below 105 M ) shine
bright during their main-sequence life Contribution to extragalactic background
light (IR) uncertain (dust reprocessing) Barely consistent with = 0.02
Metal Enrichment Limits: Pop III stars with MBH < 260 M shed most metals at
the end of their life cannot contribute more than = 10-4
Pop III stars with MBH > 260 M do not go supernova no limit
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
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How many Pop III IMBH How many Pop III IMBH remnants could there remnants could there be? be?
Madau & Rees (2001): Assume: one IMBH formed in each minihalo
that was collapsing at z=20 from a 3 peak Then: IMBH similar to SMBH = 10-5.7
IMBHs would reside ingalaxies and be sinkingtowards their centers
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
20
Finding Individual Finding Individual IMBHsIMBHs
Is there evidence for individual IMBHs? Bulge-star microlensing Galaxy centers Globular clusters Ultra-Luminous X-ray sources
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
21
Individual Black Holes From Individual Black Holes From Bulge-Star MicrolensingBulge-Star Microlensing
Seven long-timescale events were detected that show parallax: Allows mass estimate Three lenses have
M > 3 M and L < 1 L Possible BHs
First such BHs detected outside binaries! Bennett et al. (2000)
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
22
An IMBH from Bulge-An IMBH from Bulge-Star Microlensing?Star Microlensing?
MACHO-99-BLG-22 could be an IMBH if the lens is in the disk (most likely) or a stellar-mass BH if it is in the bulge.
Caveat: phase-space distribution function of lenses assumed known. Bennett et al. (2002)
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
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BHs in Galaxy CentersBHs in Galaxy Centers
BHs in galaxy centers can be found and weighed using dynamics of stars or gas
Brown et al. (1999)
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
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Measuring Stellar Measuring Stellar Motions in External Motions in External GalaxiesGalaxies
Without BH
With BH
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
25
Other Examples of Other Examples of KnownKnownSuper-massive BHsSuper-massive BHs
NGC 7052 NGC 6240
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
26
IMBHs in Galaxy IMBHs in Galaxy Centers?Centers?
BH mass vs. velocitydispersion correlation: Ferrarese & Merritt;
Gebhardt et al. hot stellar systems >70 km/s
Do all galaxies have BHs? Do IMBHs exist in
galaxy centers with < 50 km/s?
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
27
Black Hole constraints Black Hole constraints in Low Dispersion in Low Dispersion Systems Systems
AGN activity: Some very late-type galaxies are active,
e.g., NGC 4395 (Sm), POX52 (dE) BH mass estimated at MBH ~ 105 M
Stellar kinematics: only MBH upper limits Irregulars ?? Dwarf Spheroidals ?? Dwarf Ellipticals (Geha, Guhathakurta & vdM)
= 20-50 km/s; MBH < 107 M
Late-Type spirals (IC 342 Boeker, vdM & Vacca) = 33 km/s; MBH < 105.7 M
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
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Case Study: Case Study: IC 342IC 342
= 33 km/s MBH < 105.7 M (upper limit).
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
29
Central Star Clusters in Central Star Clusters in Late Type GalaxiesLate Type Galaxies
Late-type galaxies generally have nuclear star clusters M ~ 106 M Barely resolved (<0.1”)
BH measurement: Requires spatial
resolution of cluster restricted to HST data
for Local Group galaxies
Boeker et al. (2002)
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
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M33M33
Nucleus/star cluster dominates central few arcsec
HST/STIS: Gebhardt et al.,
Merritt et al. = 24 km/s MBH < 1500-3000 M
(upper limit)
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
31
Globular Clusters:Globular Clusters:G1 (Andromeda)G1 (Andromeda)
Gebhardt, Rich, Ho (2002): HST/STIS data
Unusually Massive Cluster
Nucleus Disrupted Satellite Galaxy?
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
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G1:G1: Models Models
Gebhardt et al: Same technique as for galaxies: Potential characterized by M/L (profile) and MBH
Find orbit superposition that best fits data No time evolution
Baumgardt et al: Use N-body simulations Vary initial conditions to best fit data Time evolution due to collisions and stellar evolution Scaling with N complicated
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
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G1:G1: Results Results
Gebhardt et al.:MBH = 2.0 (+1.4,-0.8) x 104
M
Baumgardt et al.:no black hole
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
34
G1:G1: Interpretation Interpretation
Agreement: Mass segregation not important in G1 (M/L)* ~ constant
Disagreement: IMBH needed to fit the data? Quoted IMBH sphere of influence: 0.035 arcsec Subtle, but detectable: compare to M33
Similar distance and dispersion BH mass upper limit 6 times smaller than G1 detection Sphere of influence < 0.006 arcsec
Reason for Disagreement: higher-order moments? Very difficult measurement …….
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
35
Globular Clusters: Globular Clusters: M15M15
High central density 1800 stars with known ground-based
velocities Guhathakurta et al. (1996)Sosin & King (1997)
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
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M15:M15: HST/STIS Project HST/STIS Project
V=13.7
V=18.1
vdM et al., Gerssen et al. (2002)
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
37
M15: M15: Observations & Observations & ReductionReduction
Observations: 0.1 arcsec slit 45-60 min at 18 slit positions G430M grating (around Mg b) Spectral pixel size ~16 km/s
Calibration complications: HST motion Correct for position of star in slit (WFPC2
Catalog) Statistical correction for blending
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
38
M15:M15: Results Results
HST/STIS: 64 stellar velocities
Combine with ground-based data R < 1 arcsec: sample tripled R < 2 arcsec: sample doubled
Non-parametric kinematic profiles
Near the center: Surprisingly large rotation = 14 km/s
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
39
M15: M15: Evidence for Evidence for Central Dark MassCentral Dark Mass
Jeans Models with constant (M/L)* MBH = 3.2 (+2.2,-2.2) x 103
M
The inferred central (M/L) increase could be due to an IMBH or to mass segregation
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
40
M15:M15: Models with Core Models with Core Collapse & Mass Collapse & Mass SegregationSegregation
Fokker Planck Models (Dull et al. 1997,2003)
Results: No BH: statistically consistent with data BH does improve fit: MBH = 1.7 (+2.7,-1.7) x 103
M
N-body models (Baumgardt et al.): similar results
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
41
M15:M15: Interpretation Interpretation Central dark mass concentration could be mass
segregation, but this does have uncertainties: Neutron stars (1.4 M)
pulsar kick velocities indicate most probably escape Heavy white dwarfs (1.0-1.4 M)
Have cooled too long to be observable Local white dwarf population centers strongly on ~0.6 M, with
rather few white dwarfs >1 M
High-mass IMF+evolution poorly constrained observationally
IMBH not ruled out Large rotation unexplained … But: no X-ray counterpart (Ho et al. 2003)
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
42
Importance of Importance of (possible) IMBHs in (possible) IMBHs in Globular ClustersGlobular Clusters
New link between formation and evolution of galaxies, globular clusters and central BHs?
Do the seeds in supermassive BHs come from globular cluster IMBHs?
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
43
IMBHs in Globular IMBHs in Globular Clusters:Clusters:What’s Next?What’s Next?
Study nearby clusters with (non-collapsed) cores
Understand rotation Study proper motions with HST Study more M31 globular clusters
with HST Improve models and data-model
comparison
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
44
Ultra-LuminousUltra-LuminousX-ray SourcesX-ray Sources
Many nearby galaxies have `Ultra-Luminous’X-ray sources (ULX)
LX > 1039 ergs/sec(if assumed isotropic) Brighter than the
Eddington limit for a normal X-ray binary
Fainter than Seyfert nuclei
Point sources
M82
Kaaret et al. (2001)
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
45
Generic Properties of Generic Properties of ULXsULXs
Off-center w.r.t. host galaxy not AGN related
No radio counterparts Often variable
not young X-ray SNe Bondi accrretion from dense ISM
insufficient Periodicity sometimes observed State transitions sometimes observed
ULXs are compact objects accreting from a binary companion
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
46
Accretion Models:Accretion Models:Isotropic Emission?Isotropic Emission?
Isotropic emission requires that the accreting objects is an IMBH (102-104 M)
Problems: How does an IMBH-star binary form? Late-stage acquisition of the binary companion
Dense stellar environment Observations: not a
unique correspondencewith star clusters
Companion star consumedin 106-7 years
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
47
Frequency of Frequency of OccurrenceOccurrence
Average ~1 ULX per 4 galaxies Strong correlation with
star formation Antennae: 17 ULXs Cartwheel: 20 ULXs Suggests association with HXRBs?
Not always associated withstar forming regions ULXs exist in some ellipticals, generally in
globular clusters Suggests association with LMXBs?
Luminosity Function continuous
Zezas & Fabbiano (2002)
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
48
Accretion Models:Accretion Models:Anisotropic emission?Anisotropic emission?
Normal binary in unusual accretion mode: Thin accretion disk with radiation-driven inhomogeneities? Short-lived anisotropic
super-Eddington stage;[think SS433 and Galactic micro-quasars]
Relativistic Beaming?
Difficult to explain most luminous ULXs LX = 1040-41 ergs/sec 1 per 100 galaxies
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
49
ULXs: Spectral ULXs: Spectral InformationInformation
ULX spectra well fit by multi-color disk black body model (or sometimes a single power-law)
Inner-disk T ~ 1-2 keV similar to XRBs
XMM-Newton spectra have revealed soft components in several sources (NGC 1313 X-1, M81 X-9) with T < 200 eV
T M-1/4 IMBH
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
50
ULX: What’s next?ULX: What’s next?
Optical counterparts few reported Systematic study
underway (Colbert, Ptak, Roye, vdM)
ULX Catalog HST Archive
Timing Spectra density breaks,
QPOs Associated with inner
stable orbit? f M-1
Roeland van der Marel - Space Telescope Science [email protected] http://www.stsci.edu/~marel
51
Conclusions:Conclusions:
The existence of IMBHs is not merely a remote possibility Predicted theoretically as the
result of realistic scenarios Might explain a number of
observational findings Much more work needed to
prove their existence unequivocally
Could be important forgravitational wave detection