Michael Küffmeier
S. G. Zaidi, C. Granzow Holm, T. Haugbølle (NBI), J. Pineda (MPE), D. Segura-Cox (Rochester), S. Reißl, C. P. Dullemond (ITA)
Disk Formation Beyond Collapse
Infall and Rejuvenation
When?
"At the beginning."
How?
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
Magnetic braking catastrophe
Angular momentum is transported too efficiently from the disk
History of modeling disk formation
Help! Where is the disk?!
Resistivities
Santos-Lima et al. 2012
Hydro
ideal MHD
non-ideal MHD
What about magnetic fields?
for pioneering work see Galli & Shu 1993 a/b
see Hennebelle et al. 2016 or Lee et al. 2021 for analytical studies
more references in reviews by Wurster & Li 2018, Tsukamoto et al. 2023 and Küffmeier 2024
non-ideal MHD is not a single parameter
Caveat!
depends on cosmic-ray ionization rate!
Effect of ionization on disk size
Küffmeier, Holm et al. in prep
ideal MHD
non-ideal MHD
\color{white}\zeta=10^{-18} \rm s^{-1}
\color{white}\zeta=10^{-17} \rm s^{-1}
\color{white}\zeta=10^{-16} \rm s^{-1}
increasing ionization rate
enhanced magnetic braking
smaller disks
100 au
100 au
Küffmeier, Zhao & Caselli 2020, see also Kobayashi et al. 2023
Observed variations:
Maps of CR-ionization rates (e.g., NGC 1333 Pineda et al. 2024, or AG 351 & AG 354 Sabatini et al. 2023)
Protostars B335 (Cabedo et al. 2023), IRAS4A, L1448-C, L1157 (Schwarz et al. 2026)
Effect of ionization
Küffmeier, Holm et al. in prep
\color{white}\zeta=10^{-18} \rm s^{-1}
\color{white}\zeta=10^{-17} \rm s^{-1}
\color{white}\zeta=10^{-16} \rm s^{-1}
increasing ionization rate
enhanced magnetic braking
smaller disks
100 au
Observed variations:
Maps of CR-ionization rates (e.g., NGC 1333 Pineda et al. 2024, or AG 351 & AG 354 Sabatini et al. 2023)
Protostars B335 (Cabedo et al. 2023), IRAS4A, L1448-C, L1157 (Schwarz et al. 2026)
Tokuda et al. 2026
interchange instability
(see Tsukamoto et al. 2023 [and references in the review] and Machida & Basu 2025)
?
Environment?
Stars form in molecular clouds
Accretion process is heterogeneous in time, in space, and among protostar.
Küffmeier, Haugbølle & Nordlund 2017
"mass accretion onto the star–disk system is filamentary, acting through accretion channels and accretion sheets"
Segura-Cox et al. 2020
"...you simply cannot look at disks with ideal MHD.
I thought you knew all of this, and the people in [---] are not impressed."
e-mail reaction after publication in 2017
Stars form in molecular clouds
Mayer et al. 2025
To zoom or not to zoom
Santos-Lima et al. 2012
Hydro
ideal MHD
non-ideal MHD
Mayer et al. 2025
100 au
Hydro
ideal MHD
non-ideal MHD
"What a waste of computing time, Alex. Same as isolated collapse models!"
Hydro
ideal MHD
non-ideal MHD
Disks solely from early collapse is not the full story.
Cores are in clouds
credit: Holm
Christian G. Holm
Zoom-in onto 9 star-disk systems: 4 pc -> sub-au
ideal MHD (paper in review; non-ideal MHD running)
isothermal parental run
barotropic equation of state for zoom-ins
average column density
code: DISPATCH
(Machida+ 2007)
\Sigma\approx 10^{22} \rm cm^{-2}
(Nordlund+ 2018)
Holm et al. in review
Core properties
Christian G. Holm
\sigma_{\rm v}=(0.34 \pm 0.04)\ \rm km\, s^{-1}
B_{\rm rms} = (53 \pm 20)\ \mu\rm G
(Li+ 2023)
\sigma_{\rm v} = 0.29 \ \rm km\, s^{-1}
10\ \mu\rm G
to
100\ \mu\rm G
(Crutcher+ 2010, Crutcher 2012)
Prestellar core properties
Observations
Holm et al. in review
Selected the most isolated!
consistent with observed profiles shown by Jaime on Monday
Disks (re)form via filamentary infall
Holm et al. in review
...but it happens earlier
smoother, and easier
the lower the ionization rate is.
\color{white}t=2 \, \rm kyr
...and YES, the disk properties are strongly affected by non-ideal MHD effects!
A few massive streamers
Christian G. Holm
Streamer criteria:
\Sigma>0.1 \rm g\, cm^{-2}
v_{\rm rad, in}>v_{\rm rot}
The density contrast relative to the environment is a factor of 4 to 6.
The streamer mass is between 0.1 and 0.4 .
The streamers persist for ~10 kyr, with mass accretion rates of .
10^{-5} \rm M_{\odot}\, yr^{-1}
\rm M_{\odot}
Holm et al. in review
Follow-up:
synthetic observations
see Shirin Zaidi's poster and Andreas Kjær Rasmussen's streamer website: https://streamer-explorer.streamlit.app/
Beyond the collapse?
Origin of accreting gas
Küffmeier, Jensen & Haugbølle '23
see also Pelkonen+ 2021 and poster by Shingo Nozaki
Origin of accreting gas
Kaalva, Offner, Filippova & Grudic '26
Animation by S. Raymond
Credit: Garufi et al. 2024
Disks are rarely isolated.
Streamers and shadows as signs of infall-induced disks
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
Two phases of disk formation
Küffmeier, Winter, Kuznetsova et al. in prep
Summary
Disks are replenished and distorted by filamentary infall (streamers).
Star and disk formation is a two-phase process consisting of mandatory initial collapse and post-collapse ("late") infall phase.
The degree of ionization is important for disk properties, but large delivery of angular momentum simplifies disk formation after very early collapse phase.
To do
...solely replenishes the disk,
I
...plays an active role in triggering instabilities,
II
...induces dramatic changes such as misalignment.
III
Explore frequency and properties of infall onto star-disk systems that ...
images: A. Houge
Copy of Prestellar core workshop Kyushu 2026
By kuffmeier
