What we know, think to know, and don't know about disk formation
Michael Küffmeier
How did it begin?
Astrophysics and planetary science department
Credit: Christian G. Holm
...
and what happened later?
Stars form in molecular clouds
NASA, ESA, CSA and STScI
2. Filaments form inside the cloud
3. Dense cores form inside the filaments
1. Giant Molecular Cloud of gas and dust
From giant molecular clouds to protostars
4a. Stars form from the collapse of dense cores
4b. Rotation in the cloud leads to the formation of a disk
5. Planets form in the disk
~1 to 10 Myr
~1 to 100 pc
The classical picture
credit: M. Persson
star formation
planet formation
t ~ 10 to 100 kyr
t = 0 kyr
t ~ 100 to 500 kyr
t ~ 1 Myr
t ~ 10 Myr
t ~ 1 to 10 Gyr
Let's go back in time to the year 2014
Wow!
Credit: ALMA (ESO/NAOJ/NRAO)
Credit:
DSHARP team
10 au
50 au
Credit: NASA/ESA Hubble space telescope &
ALMA (ESO/NAOJ/NRAO)
The big challenge:
link planet to star formation
50 au
History of modeling disk formation
spherical core collapse:
rotation
magnetization (mass-to-flux ratio)
non-ideal MHD effects
dust evolution
turbulence
useful for parameter studies
\rho(r) = \frac{\rho_{\rm c} R_{\rm c}^2}{R_{\rm c}^2 + r^2}
Bonnor-Ebert sphere
or uniform density
\rho(r) = \rho_{0}
History of modeling disk formation
What about magnetic fields?
Help! Where is the disk?!
Santos-Lima et al. 2012
Hydro
ideal MHD
L_{\rm mag} = \int_{t_{\rm c}}^{t}\int^V r (\mathbf{J} \times \mathbf{B})_\phi \mathrm{d}V\mathrm{d}t
Magnetic braking catastrophe
Angular momentum is transported too efficiently away from the disk
magnetohydrodynamics
\frac{\partial \mathbf{B}}{\partial t} = \nabla\times (\mathbf{v}\times\mathbf{B})
ideal MHD
\color{red}-\nabla\times[\eta_{\rm O} (\nabla \times \mathbf{B})]
\color{purple}-\nabla\times \{\eta_{\rm H} [(\nabla \times \mathbf{B}) \times \mathbf{B}/B] \}
\color{blue}-\nabla\times \{\eta_{\rm AD} \mathbf{B}/B \times [(\nabla \times \mathbf{B}) \times \mathbf{B}/B] \}
Ohmic dissipation
Hall
ambipolar diffusion
Non-ideal
Non-ideal MHD
Masson et al. 2016
\frac{\partial \mathbf{B}}{\partial t} = \nabla\times (\mathbf{v}\times\mathbf{B})
\color{red}-\nabla\times[\eta_{\rm O} (\nabla \times \mathbf{B})]
\color{purple}-\nabla\times \{\eta_{\rm H} [(\nabla \times \mathbf{B}) \times \mathbf{B}/B] \}
\color{blue}-\nabla\times \{\eta_{\rm AD} \mathbf{B}/B \times [(\nabla \times \mathbf{B}) \times \mathbf{B}/B] \}
resistivities quench pile-up of magnetic field
avoids magnetic braking catastrophe
see Hennebelle et al. 2016 or Lee et al. 2021 for analytical studies
more references in Wurster & Li 2018 (review)
History of modeling disk formation
What about magnetic fields?
Help! Where is the disk?!
Ohmic, Ambipolar, Hall
Santos-Lima et al. 2012
Hydro
ideal MHD
non-ideal MHD
non-ideal MHD is not a single parameter that is turned on or off
Achtung!
if you are curious to learn more about theory of MHD, talk to Martin Pessah at Niels Bohr International Academy
Resistivity depends on ionization rate
Küffmeier, Zhao & Caselli 2020
Question: What is the effect on disk formation when differing the ionization rate?
Effect of ionization on disk size
increasing ionization rate
enhanced magnetic braking
smaller disks
Küffmeier, Zhao & Caselli 2020
rotation
infall
from light to dark colors: high to low ionization rates
see also Wurster et al. 2018
Disk size distribution
Küffmeier, Zhao & Caselli 2020
mass-to-flux ratio
initial strength of rotation
What about magnetic fields?
Help! Where is the disk?!
Ohmic, Ambipolar, Hall
Turbulence
Santos-Lima et al. 2012
Hydro
ideal MHD
non-ideal MHD
turbulence + MHD
Other effect: dust
dust growth weakens magnetic braking => larger disks
Zhao et al. 2018, Marchand et al. 2020
dust-rich disks from collapse
"ash-fall" scenario
Tsukamoto et al. 2021
Lebreuilly et al. 2020
dust accumulates
History of modeling disk formation
What fraction of the gas and dust returns to the disk after being ejected by an outflow?
Credit: Tsukamoto et al. 2021
"Ash-fall" scenario aka conveyor belt
if you are curious about dust growth that leads to planet formation talk to:
Troels Haugbølle, Anders Johansen, Michiel Lambrechts, Anja Andersen or me
Is this the full picture?
Credit: ALMA (ESO/NAOJ/NRAO)
Ginski et al. 2021
Yen et al. 2019
Garufi et al. 2021
Pineda et al. 2020
50 au
BHB1 (Alves et al. 2020), GM Aur (Huang et al. 2021), IRS 63 (Podio et al. 2024, Segura-Cox in prep.), AB Aur (Grady et al. 1999 / Fukagawa et al. 2004), M512 Grant et al. 2021, Gupta et al. 2024, Cacciapuoti et al. 2024), PPVII review by Pineda et al. 2023
Per-emb-50
Valdivia-Mena et al. 2022 (see poster!)
Streamers:
if you want to work on disk observations, reach out to Jes Jørgensen or Giulia Perotti
Zoom-in method
Küffmeier et al. 2017
- ideal magnetohydrodynamics
- adaptive mesh refinement
1pc ≈ 206 265 au
Text
Adaptive mesh refinement
Adaptive mesh refinement
Zoom-in on embedded protostars
Küffmeier, Calcutt & Kristensen 2019
bridge structure similar to IRAS 16293--2422 (e.g. Sadavoy+ 2018, van der Wiel+ 2019, Maureira+ 2020)
Küffmeier, Reißl et al. 2020
~1500 AU
Küffmeier et al. 2018
How does (early) infall shape disk formation?
Christian G. Holm
Zoom-in simulation, ~1 au resolution in disk, barotropic equation of state
Simulations: Christian G. Holm, Troels Haugbølle
Visualizations: Thomas Berlok
Late infall is common for stars
On average, even solar mass stars gain ~50 % of their final mass through accretion of initially unbound material
Note that some protostars still accrete after 1.2 Myr
Küffmeier, Jensen & Haugbølle '23
(Pelkonen et al. 2021)
Two phase accretion process
Initial collapse followed by varying amount of post-collapse infall
(see also Smith+ 2011, Padoan et al. 2020, Pelkonen+ 2021)
Küffmeier, Jensen & Haugbølle '23
Origin of accreting gas
"In the case of the more massive stars, accretion from the environment outside the original core volume is even more important than that from the core itself. [...]
The assumption of spherical symmetry cannot be applied to the majority of collapsing cores, and is never a good description of how stars accrete gas from outside the original core radius."
(Smith et al. 2011)
YSOs can appear younger than they really are
How old is the protostar?
Küffmeier, Jensen & Haugbølle '23
Class I
Class 0
Class II
A poor analogy to a lecture
Session start
Coffee break!
Streamers (and shadows) as signs of infall
Formation of misaligned configuration
Observable as shadows in outer disk
Küffmeier, Dullemond, Reissl & Goicovic 2021
SU Aur (Ginski et al. 2021)
300 au
Krieger, Küffmeier et al. 2024
- Is the disk solely replenished with fresh material?
- Does infall frequently lead to the formation of a new misaligned outer disk (and if yes, for how long)?
- Is (late) infall catastrophic? Does a completely new disk form?
Key questions to be addressed in the future
Summary
Disks are replenished, distorted or even destroyed by misaligned infall
Protostellar environment matters
Star formation is a two-phase process consisting of mandatory initial collapse and post-collapse infall phase
Küffmeier 2024
Credit:
M. Lützen
Revised picture
Pineda et al. 'Protostars and Planets VII'
.
.
Segura-Cox et al. in prep.
Star and planet formation are two sides of the same coin
The disk is not a static entity, but rather a buffer zone
*we haven't even touched (proto-)stellar multiplicity
Lecture astro1 250924
By kuffmeier
