Åke nordlund centre for star and planet formation and niels bohr institute university of copenhagen
TRANSCRIPT
Åke Nordlund
Centre for Star and Planet Formationand
Niels Bohr Institute
University of Copenhagen
Brown Dwarfs and Massive Planets What’s the difference?
Brown Dwarf Formation Turbulent fragmentation Interrupted accretion
Planet Formation Core accretion Gravitational instability Cosmochemical evidence new and severe constraints new paradigm for planet formation
Star formation (vastly better understood than planet formation!)
Formation of GMCs in the Galaxy de Avillez et al 2004-2010
Formation of MCs in GMc Kritsuk et al 2010
Formation of stars in MCs Padoan & Nordlund 2010
10003 cells, Mach 9 supersonic MHD-turbulencePadoan & Nordlund (2010)
Brown Dwarfs are marked with black dots, more massive
stars with white dots.
Brown Dwarfs are marked with black dots, more massive
stars with white dots.
Padoan, Kritsuk, Norman (2005)
Padoan, Kritsuk, Norman (2005)
Padoan, Kritsuk, Norman (2005)
Mass accreting from the ’envelope’ is not likely to be distributed in a smooth and
symmetric fashion
Mass accreting from the ’envelope’ is not likely to be distributed in a smooth and
symmetric fashion
Core Accretion Barely fast enough in the SS; Jupiter (and Saturn?)
Very difficult to explain Jupiter’s abundance pattern Much too slow at current Uranus & Neptune
Enter Nice model... Much too slow for wide orbit M-dwarf gas giants
Hello Nice? Excentric and non-coplanar orbits
?? Type I migration
arbitrary (and large) pre-factors
Current Paradigm: Start out with planetisimals + some remnant gas So, separation must have happened earlier!? Let’s back up to that time then:
Gas + dust in a disk Can gas and dust be separated? Yes, easily!
Just read Weidenshilling (1977) Unfortunately, the Sun devours the Z, leaves an X+Y disk
The CAI and AOA inclusions have condensed out of a dense, 26Al rich gas phase
The CAI and AOA inclusions have condensed out of a dense, 26Al rich gas phase
CAI = Calcium Aluminum InclusionsCAI = Calcium Aluminum Inclusions
AOA= Amoeboid Olivine AggregatesAOA= Amoeboid Olivine Aggregates
26Al is radio-active, with a 750.000 yr half-life Can be used as a very accurate clock, if initially uniform
It was present in the early Solar System Enough to melt bodies larger than about 50-100 km Need this bodies to form quickly!
It originates in ordinary supernovae Was transported to the early Solar System in a few Myr
Now (in press) has shown to be subjected to ”thermal processing” (T > 1500 K) in the early SS
From the reproducibility btw samples, the time scale of
formation of the first solids in the Solar System was
only a few thousand yrs!
From the reproducibility btw samples, the time scale of
formation of the first solids in the Solar System was
only a few thousand yrs!
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The conclusion from this correlation is that 26Al was
initially homogeously distrubuted, but suffered
thermal processing
The conclusion from this correlation is that 26Al was
initially homogeously distrubuted, but suffered
thermal processing
Cf. Johansen & Lacerda (2010) ”Pebble accretion” onto planetesimals ”Doubles the mass in less than 150 years”
Cf. Johansen & Lacerda (2010) ”Pebble accretion” onto planetesimals ”Doubles the mass in less than 150 years”
Why should it stop there? Technical reasons:
Periodic box constrained growth (Johansen) Planetesimal Hill radius not resolved (Boley)
No physical reasons: Hill radius keeps growing: volume proportional to mass Unlike the end of run-away growth; excitation does not kill it
Gas - Fractionation
Migration
XYZ - Gravity
Z / XY - Separation
Z - Accretion
Gas - Accretion
XYZ - Gravity
Z - Accretion
Gas – Fractionation
Z / XY - Separation
Z - Accretion
Gas - Accretion Z / XY - Separation
Approximate log-spacing of plants Gregory (1715) Titius (1766) Bode (1772) Hayes & Tremain (1998) Poveda & Lara (2008) Lovis et al (2010)
Consider the no. of Hill radii ...
Spacings are clearly approximately logarithmic
(including in the SS), but the number of Hill radii seems
superficially to have nothing to do with it
Spacings are clearly approximately logarithmic
(including in the SS), but the number of Hill radii seems
superficially to have nothing to do with it
However, if the total (XY+Z) initial mass is used, all gaps are
similar, in terms of Hill radii!
However, if the total (XY+Z) initial mass is used, all gaps are
similar, in terms of Hill radii!
Brown Dwarfs can form the same way other stars form Turbulent fragmentation in cold molecular gas BD mass fragments are exceedingly numerous, but ... ... only a tiny fraction are dense enough to collapse into BDs Successful fragments are confined by very large dynamic
pressure (smooth convergence + shock)
Brown Dwarfs and Massive Planets Similar structure, but two modes of formation
direct, gravitational, by turbulent compression indirect, assisted by (rapid!) core formation
Some massive ’planets’ in excentric, non-aligned orbits may form through the indirect (BD-like) mode