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

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

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

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,

...plays an active role in triggering instabilities,

...induces dramatic changes such as misalignment.

III

Explore frequency and properties of infall onto star-disk systems that ...

images: A. Houge