Michael Küffmeier (Carlsberg reintegration fellow)
Infall: crucial, yet underrated
Sigurd Jensen, Jaime Pineda, Paola Caselli (MPE), Christian G. Holm, Troels Haugbølle (NBI), Stefan Reißl, Kees Dullemond (ITA)
SU Aur
synthetic image
Outline
Overview and history of star-disk formation
I
Revisiting star-disk formation from a Giant Molecular Cloud perspective
II
Open questions, future plans and ideas
IV
Summary
V
Implications of (late) infall
III
Overview and history of star-disk formation
Let's go back in time to the year 2014
Wow!
Credit: ALMA (ESO/NAOJ/NRAO)
Credit:
DSHARP team
10 au
50 au
The classical picture
credit: M. Persson
star formation
planet formation
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
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 reviews by Wurster & Li 2018 and Tsukamoto et al. 2023
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
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!
It depends on ionization fraction.
Achtung!
see Wurster et al. 2018, Kuffmeier et al. 2020; reviews by Tsukamoto et al. 2023, Kuffmeier submitted
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
History of modeling disk formation
Revisiting star-disk formation from a Giant Molecular Cloud perspective
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 (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) ...
Per-emb-50
Valdivia-Mena et al. 2022
Science question:
Can we get better (statistical) constraints on the relevance and importance of (late) infall from existing simulation data?
Streamers:
Model star formation in a Molecular Cloud
isothermal magnetohydrodynamical (MHD) with driven turbulence
adaptive mesh refinement (AMR) simulations with RAMSES
maximum resolution: ≈25 au (level of refinement: 15), root grid about ≈1600 au (level 9)
Total mass: 3000 solar masses
periodic boundary conditions
altogether 321 sink particles at last snapshot (2 Myr after the formation of the first star)
simulation setup including detailed description of sink recipe presented in Haugbølle+2018
Küffmeier, Jensen & Haugbølle '23
Late infall is common for stars*
*unless they remain tiny
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)
Origin of accreting gas
Two phase process:
Initial collapse followed by varying amount of post-collapse infall
(see also Smith+ 2011, Kuznetsova 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)
Implications of (late) infall
YSOs can appear younger than they really are
How old is the protostar?
Küffmeier, Jensen & Haugbølle '23
Class I
Class 0
Class II
Implications for Al-26 heterogeneity
Küffmeier et al. 2016
- Gas is well-mixed within core, and hence Al-26 abundance is fixed during CAI formation (t<~100 kyr).
- BUT: significant deviations in Al-26 abundance beyond the core may likely be imprinted on disk afterwards!
Spreading vs wind-driven?
Manara et al. 2023
Misleading!
Infall matters. Disks can easily be wind-driven and yet grow in size through infall of gas with high angular momentum.
Long et al. 2022
Angular momentum budget
- Large scatter of ang. mom.
- Increasing specific angular momentum for increasing final stellar mass
Specific angular momentum computed from all accreting tracer particles at the first snapshot after star formation
- subtle correlation with mass (inherited by disks??)
"We find marginal relationships between disk sizes and M*." (Long+ 2022)
Küffmeier, Jensen & Haugbølle '23
Long et al. 2022
On average, stars with increasing final mass undergo prolonged infall
Orientation of star-disk systems can change substantially
Orientation of infall
Küffmeier, Haugbølle, Pineda & Segura-Cox submitted
How to quantify anisotropy of accretion?
FA = 0: perfectly isotropic accretion
FA = 1: maximally anisotropic accretion
Küffmeier, Haugbølle, Pineda & Segura-Cox submitted
Fractional anisotropy based on tracer particles
Post-collapse infall is more anisotropic than initial collapse
Post-collapse infall is more anisotropic than initial collapse
Anisotropic accretion
FA = 0: perfectly isotropic accretion
FA = 1: maximum anisotropic accretion
Küffmeier, Haugbølle, Pineda & Segura-Cox submitted
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
Do we really know disk "lifetimes"?
Polnitzky et al. 2024 in prep
Fraction reflecting occurrence of infall events instead of disk age?
Open questions, future plans and ideas
Credit: NASA/ESA Hubble space telescope &
ALMA (ESO/NAOJ/NRAO)
The big challenge:
link planet to star formation
50 au
Zoom-in on embedded stars
Küffmeier et al.
2019
Küffmeier et al. 2018
Küffmeier, Reißl et al. 2020
bridge structure similar to IRAS 16293--2422 (e.g. Sadavoy+ 2018, van der Wiel+ 2019, Maureira+ 2020)
~1500 AU
Pro: self-consistent initial and boundary conditions for star formation
Con: computationally more expensive, more difficult analysis
for a similar concept, see also Lebreuilly et al. 2024
Simulations: Holm, Haugbølle
Visualizations: Berlok
How do infall and outflow affect the disk?
Christian G. Holm
Zoom-in simulation*, ~1 au resolution in disk, barotropic equation of state
*(run with DISPATCH: used only 1 instead of 24 nodes, yet faster than RAMSES)
- 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 multi-scale models
Summary
Disks are replenished, distorted or even destroyed by misaligned infall
Young Stellar Objects can be rejuvenated
Star formation is a two-phase process consisting of mandatory initial collapse and post-collapse infall phase
Lützen & Küffmeier
Christian G. Holm
How do infall and outflow affect the disk?
Angular momentum transport via magnetic braking
What fraction of the gas and dust returns to the disk after being ejected by an outflow?
Key question
Credit: Tsukamoto et al. 2021
"Ash-fall" scenario aka conveyor belt
Increase in dust-to-gas ratio because dust can grow in disk and return
Tsukamoto et al. 2021
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
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
Effect of ionization on disk size
increasing ionization rate
enhanced magnetic braking
smaller disks
see also Wurster et al. 2018
Küffmeier, Zhao & Caselli 2020
Starplan retreat 2024
By kuffmeier
