Disk fragmentation,

1
Disk fragmentation, the Brown Dwarf Desert, and
the Stellar Upper Mass Limit
Chris Matzner University of Toronto
Yuri Levin, U. Leiden
Kaitlin Kratter, U. Toronto
2
Disk fragmentation in the main accretion phase
Which protostellar disks accrete stably, and
which undergo gravitational fragmentation?
Fragmentation is sensitive to the thermal
evolution of the disk see posters by Kai,
Stamatellos
Patel et al 04
3
Gammie 2001
Disk fragments when
and
Most useful for - Self-luminous disks with
negligible irradiation - Setting lower limits
on the radius of fragmentation and Mfrag
Rafikov Whitworth Stamatellos
4
Gammie 2001
Disk fragments when
This form is most useful for - Disks heated by
irradiation as well as viscosity - Disks with
imposed mass accretion
5
Fed by collapsing mol. core
Implication A disk fragments if it is cooler
than its core
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Low-mass star formation
CDM Y.Levin 2005
Disk fragments when
Accretion heating alone stabilizes the disk for
periods less than a few centuries.
see poster by Stamatellos
Irradiation by reprocessed starlight can
stabilize it out to thousands of years!
see poster by Kai
7
Grether Lineweaver 2006
Stabilized by irradiation
Stabilized by viscous heating
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Massive star formation
Kratter CDM 2006
Destabilizing effect
More rapid accretion fragment when
Stabilizing effect More luminous central star
Which wins?
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Kratter CDM 2006
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Observers-eye view
Kratter CDM 2006
toroids
disks
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Theorists-eye view
Kratter CDM 2006
McKee Tan 2003 (fiducial model)
Sharp drop in dust opacity at high accn rates
Fragmentation accelerates as mass increases
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Stellar upper mass limit If not radiation
pressure, then disk fragmentation? Few other
mechanisms get worse above a threshold
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Conclusions Challenges
For Numericists Isothermal codes should make
too many BDs by disk fragmentation
Radiation-diffusion stabilize out to century
periods Irradiation, outflow cavity stabilize
even further
For Observers Find 0.1-1 (or more)
companions 150 AU (or less) from young
O stars Find gravitational spirals in the gas
For Theorists Brown Dwarf Desert and upper mass
limit are both made in disks? Must account for
magnetic fields! Must model global modes for
massive disks.
(w/ M. Krumholz K. Kratter)