Michael Küffmeier

The interplay of multiplicity and infall

C. Granzow Holm (GLOBE), T. Haugbølle (NBI), J. Pineda (MPE), D. Segura-Cox (Rochester)

DFF Sapere Aude group leader

Michael Küffmeier

C. Granzow Holm (GLOBE), T. Haugbølle (NBI), J. Pineda (MPE), D. Segura-Cox (Rochester)

The interplay of

multiplicity and infall

DFF Sapere Aude group leader

Michael Küffmeier

C. Granzow Holm (GLOBE), T. Haugbølle (NBI), J. Pineda (MPE), D. Segura-Cox (Rochester)

DFF Sapere Aude group leader

The interplay of

multiplicity and infall

The classical picture

credit: M. Persson

star formation

planet formation

Problems

No multiplicity

No infall

Is this the full picture?

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}

Sequence of star, disk & planet formation

Illustration: Segura-Cox (published in Pineda et al. 2023)

better, but let's keep in mind:

star formation is a dynamical process happening in turbulent molecular clouds

Revisiting star-disk formation from a Giant Molecular Cloud perspective

Zoom-in simulations

Christian G. Holm

Pro: self-consistent initial and boundary conditions for star formation

Con: computationally more expensive, more difficult analysis

Zoom-in on embedded multiples

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

for a similar concept, see also Lebreuilly et al. 2024, Yang & Federrath 2025

Formation of embedded protostellar multiple

Küffmeier et al. 2019

Jacobsen et al. 2019

IRAS 16293-2422

636 au

Zoom-in simulation

Transient "bridge"-structures* (τ~10 kyr) are a common by-product of turbulent fragmentation

*Could be easily classified as "streamer" during "bridge" dispersal because material accretes towards the companion with highest gravitational potential

Formation of embedded protostellar multiple

Küffmeier+ 2019

Küffmeier+ 2019

Lee, Offner+ 2019

Dong+ '22

credit to simulation: Cuello

Is Z CMa a by-product of multiplicity formation, stellar flyby or something else?

Transient "bridge"-structures (τ~10 kyr) are common

Formation of embedded protostellar multiple

Close binaries can form wide

(for statistical analysis of binary formation see Kuruwita & Haugbølle '23; for comprehensive overview of formation pathways see talk by K. Kratter )

Periodic episodic accretion

Possible explanation for wobbly, perpendicular jets in NGC1333-IRAS2A VLA1/2 (Jørgensen+ '22)

Küffmeier+ '19

What fraction of close binaries formed wide?

recall also talk by A. Vigna Gomez and see talk by E. Bordier

Formation of embedded protostellar multiple

Multiples can share accretion reservoir

Küffmeier+ '19

The colored dots show the location of gas accreting onto primary (black), secondary (cyan) and tertiary (red) at t=20 kyr after primary formation.

Shared mass reservoir of binary

zoom-in: max. resolution 3 AU; barotropic eq. of state; ideal MHD (simulations by T. Haugbølle)

1000 au

Accreting from companion's disk

Caveat: zoom-in with only maximum resolution of 3 AU; barotropic equation of state; ideal MHD (more to be done, but intriguing)

about 30 % of accreting mass goes through the star's own disk

almost 10 % of accreting mass of companion goes through the primary star's disk

preliminary

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)

3000 solar masses; periodic boundary conditions; 321 sinks forming within 2 Myr

simulation setup including detailed description of sink recipe presented in Haugbølle+2018

image based on Küffmeier, Jensen & Haugbølle '23

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)

Origin of accreting gas

Two phase process:

Initial collapse followed by varying amount of post-collapse infall

(see also 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, Glover, Bonnell, Clark & Klessen 2011)

model for massive star formation: inertial-inflow model (Padoan+ '20)

Infall & multiplicity scale with stellar mass

based on Pelkonen+ '21

Offner+ '23

What is the connection?

(see talks by D. Taylor, T. M. Valdivia Mena, D. Price, C. Gieser, J. Pineda)

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

see also talk by R. Al Belmpeisi and V. Tuhtan

Spreading vs wind-driven?

Manara et al. 2023

Caveat!

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

see also Padon+ '05 & '25 and Winter+ '24 for analyses/discussions of Bondi-Hoyle(-Lyttleton) accretion

Padoan+ '25

Do we really know disk "lifetimes"?

Polnitzky et al. 2024 in prep

Does disk fraction reflect occurrence of infall events instead of disk age?

see also talk by D. Price on multiplicity and why the static disk framework is wrong in interpreting planet formation

On average, stars with increasing final mass undergo prolonged infall

Orientation of star-disk systems can change substantially

Orientation of infall

Küffmeier, Pineda, Segura-Cox & Haugbølle 2024

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

Misaligned disks can also be induced by companions (see talks by I. Rabago, J. Smallwood).

Is there a predominant mechanism causing misalignment?

Orientation of infall

...

A disk contains only 1% of the stellar mass:

"Easy" to replenish with post-collapse (late) misaligned infall.

Turbulence matters from cloud to core (Padoan+ '97/'20, Klessen '01, Padoan & Nordlund '02, Hennebelle & Chabrier '08), down to binary (Offner+ '10) and disk scales (Küffmeier+ '17)

It implies misaligned infall (Küffmeier+ '24, Pelkonen+ '25), i.e., "chaotic star formation" (Bate '10)

and primordial misaligned disks (Thies+ '11, Bate '18, Küffmeier+ '21)

State-of-the-art in theory of star formation

How important is multiplicity in ejecting run-away stars?

How to quantify anisotropy of accretion?

FA = 0: perfectly isotropic accretion

FA = 1: maximally anisotropic accretion

Fractional anisotropy based on tracer particles

Post-collapse infall is more anisotropic than initial collapse

Post-collapse accretion phase resembles Bondi-Hoyle(-Lyttleton) accretion

Küffmeier, Pineda, Segura-Cox & Haugbølle 2024

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 2024

Late infall is more anisotropic than early collapse

\mathrm{FA} = \sqrt{ \frac{1}{2}} \frac{\sqrt{(\lambda_1 - \lambda_2)^2 + (\lambda_2 - \lambda_3)^2 + (\lambda_3 - \lambda_1)^2}}{\sqrt{\lambda_1^2 + \lambda_2^2 + \lambda_3^2}}

Fractional anisotropy (FA) serves as a good measure for the (an-)isotropy of accretion.

FA=0: perfectly isotropic accretion, FA=1: maximally anisotropic