dead zones and the growth of giant planets
Post on 30-Jan-2016
69 Views
Preview:
DESCRIPTION
TRANSCRIPT
Dead zones and Dead zones and the growth ofthe growth ofgiant planetsgiant planets
Ralph PudritzRalph Pudritz(McMaster University)(McMaster University)
Soko MatsumuraSoko Matsumura(Ph.D. McMaster; PDF Northwestern) (Ph.D. McMaster; PDF Northwestern)
Ed ThommesEd Thommes(CITA: Norwestern)(CITA: Norwestern)
OutlineOutline
1. Planet formation – disks and gaps1. Planet formation – disks and gaps
2. Dead zones (DZs) 2. Dead zones (DZs)
3. Gap opening masses in disks with DZs3. Gap opening masses in disks with DZs
4. Dead zones and planetary migration – step 14. Dead zones and planetary migration – step 1
The PointThe Point: Dead zones (=no MRI turbulence) : Dead zones (=no MRI turbulence) expected from first principles – they shape expected from first principles – they shape both planetary masses + halt planetary both planetary masses + halt planetary migration migration
Extrasolar Planets: Extrasolar Planets:
Several thousands Several thousands of solar type stars of solar type stars surveyed – 5 – 20% surveyed – 5 – 20% have planets within have planets within 5 AU.5 AU.
More than 200 now More than 200 now knownknown
Question:Question: what what halted migration in halted migration in (some?) systems?(some?) systems?
Gas Accretion & Gap-formation
HH 30 (from HST)
Flared, gaseous, dusty disk
http://www.astro.psu.edu/users/niel/astro1/slideshows/class43/slides-43.html
Protoplanet
Protoplanetary disks – from
cores to planets
1. Planet Formation – Disks and Gaps1. Planet Formation – Disks and Gaps
Giant planet formation; two mechanisms under intense Giant planet formation; two mechanisms under intense investigation:investigation:
1. 1. Core accretion modelCore accretion model…. Coagulation of …. Coagulation of
planetesimals that when exceeding 10 Earth masses, planetesimals that when exceeding 10 Earth masses, gravitationally captures gaseous envelope (eg. gravitationally captures gaseous envelope (eg. Bodenheimer & Pollack 1986)Bodenheimer & Pollack 1986)
2. 2. Gravitational instability modelGravitational instability model …. GI in Toomre …. GI in Toomre unstable disk produces Jovian mass objects in one go unstable disk produces Jovian mass objects in one go (eg. Boss 1998).(eg. Boss 1998).
For either 1 or 2 – For either 1 or 2 – final mass determined by “gap final mass determined by “gap opening”opening” in face of disk “viscosity”. in face of disk “viscosity”.
Protoplanet
Tidal Torque
Viscous Torque
Disk
Disk
Gap opens in a disk when
Tidal Torque ~
Viscous Torque
When planets start to appear…
Gap-opening masses of a Planet
- Gap-opening mass ~ Final mass of a planet - Two competing forces (Tidal vs Viscous) - Smaller gap-opening masses in an inviscid disk
Need to know - disk flaring (h/a) - viscosity
),(3
23
a
hQF
a
h
M
M
Star
Planet
(In an inviscid disk)
Rafikov (2002)
5
40
a
h
M
M
Star
Planet (In a viscous disk)
Lin & Papaloizou (1993)
Disk Radius a [AU]
Disk pressure scale height h [AU]
(Matsumura & Pudritz 2005, ApJL; 2006, MNRAS)
Chiang and Goldreich (1997)
Submm Infrared Optical
Disk structure – reprocessing stellar radiation
Radiative resprocessing: hydrostatic equilibrium disk
models
1: Disk Surface Tds
2: Disk Interior Ti
- Most promising source of viscosity: Magneto-rotational instability (MRI) turbulence (Balbus & Hawley, 1991) Dead Zone: where MRI is inactive (Gammie 1996) -> In sufficiently poorly ionized region, Ohmic dissipation damps out MRI
MRI active region: Disk is well-ionized -> MRI turbulence - Larger gap-opening mass for larger viscosity
2. Dead Zones
Ionization: X-rays cosmic rays radioactive elements thermal collisions of alkali ions
Dead Zones (no turbulence region in central disk)
X-rays
Dead Zone
Cosmic rays magnetic field
RA elements
Recombination: metal ions molecular ions grains
Dead Zone (Gammie, 1998):
- Ionization rate is very low
- Magneto-rotational instability (MRI) turbulence is inactive
- .. So disk’s viscosity is low there
3. Dead Zones in Chiang-Goldreich models
Disk Radius [AU] 0.01 0.1 1 10 100
100
10
1
0.1
0.01
0.001
0.0001
Dis
k H
eigh
t [A
U]
~ 13 AU
Our dead zones include entire pressure scale
height h of colder mid-plane (also
include critical column density
ratio for excitation of
motion at midplane by
turbulence in envelope).(Matsumura & Pudritz; 2005, 2006)
Gap-opening masses of Planets
Disk Radius [AU] 0.01 0.1 1 10 100
100
10
1
0.1
0.01
0.001
0.0001
Gap
-ope
ning
mas
s [
MJ]
Jupiter
Uranus or
Neptune
Earth
Even a terrestrial mass planet opens a gap in a DZ!!
4. Dead zones and planetary migration – step 1
1. eg. Type I migration (before gap-opening)
→ 10 MEarth (< MUranus)
Dead Zone
Star Protoplanet
Numerical Technique:
We use a hybrid numerical code combining N-body symplectic integrator SYMBA (Duncan et al 1998) with evolution equation for gas (Thommes 2005)
-Allows us to follow evolution of planet and disk for disk lifetime: 3 – 10 Million years.
(Matsumura, Pudritz, & Thommes 2006)
Planetary migration: planet – disk interaction Planetary migration: planet – disk interaction (eg. Ward 1997)(eg. Ward 1997)
Planet exerts tidal torque at Lindblad Planet exerts tidal torque at Lindblad resonances in disk. resonances in disk.
This excites spiral density waves - propagate This excites spiral density waves - propagate away from resonances + spread angular away from resonances + spread angular momentum throughout diskmomentum throughout disk
PROBLEM: Migration too efficient… lose PROBLEM: Migration too efficient… lose planets in a million years!planets in a million years!
QUESTIONQUESTION: What saves planetary systems?: What saves planetary systems?
10 ME: Type I migration (No Gap-opening)
30
20
10
0
Dis
k R
adiu
s [A
U]
0 2×106 4×106 6×106 8×106 107
Time [years](w/o Dead Zone)
=10-5
30
20
10
0
Dis
k R
adiu
s [A
U]
0 2×106 4×106 6×106 8×106 107
Time [years](w/ Dead Zone)
Dead Zone
=10-2=10-2
Evolution of disk column density during gap openingEvolution of disk column density during gap opening
.10;10;10;10 7654 yrt
Note pile up of
material at outer edge of
dead zone. This
denstiy gradient deflects
migration of outer
light planets.
If planet forms within the DZ:If planet forms within the DZ:halt migration of terrestrial planets by opening a gap in the halt migration of terrestrial planets by opening a gap in the
DZDZ
10 M_E planet started in dead zone; Left 2 million yrs Viscosity:
25 10;10 SSdz
Type II migration (After Gap-opening)
30
20
10
0
Dis
k R
adiu
s [A
U]
0 2×106 4×106 6×106 8×106 107
Time [years](w/o Dead Zone)
30
20
10
0
Dis
k R
adiu
s [A
U]
0 2×106 4×106 6×106 8×106 107
Time [years]
(w/ Dead Zone)
=10-3 =10-3
=10-5
Dead Zone
Migration of Migration of a Jovian a Jovian planet over planet over 10 Myr.10 Myr.
- Note extent Note extent of gap of gap opened by opened by planet once planet once inside dead inside dead zone. (But zone. (But see Soko’s see Soko’s following following talk)talk)
- Planet Planet started at started at 20 AU 20 AU settles into settles into orbit at 4AU orbit at 4AU after 10 Myrafter 10 Myr
10 M10 MEE opens opens
gap at 3.5 gap at 3.5 AU in dead AU in dead zonezone
Also:Also:
1 M1 MEE opens opens
gap near 0.1 gap near 0.1 AU AU
- Look for - Look for this…this…
SummarySummary DZs are inescapableDZs are inescapable – (physics of MRI + high – (physics of MRI + high
column density of protostellar disks)column density of protostellar disks) DZs -> sharp radius beyond whichDZs -> sharp radius beyond which massive planets form (initially beyond 10 AU)massive planets form (initially beyond 10 AU) DZs -> terrestrial planets open gaps within DZs -> terrestrial planets open gaps within
them –> halt rapid loss of terrestrial planet them –> halt rapid loss of terrestrial planet cores…. hope for Kepler mission?cores…. hope for Kepler mission?
Outer edge of DZ – very interesting place for Outer edge of DZ – very interesting place for GI instabilities? GI instabilities?
QuestionQuestion: how do planets accrete as they : how do planets accrete as they
migrate in evolving disks? See Soko’s talk….migrate in evolving disks? See Soko’s talk….
top related