Infall: crucial, yet underrated

Michael Küffmeier

C. P. Dullemond, F. Goicovic, S. Reißl, T. Haugbølle, Å. Nordlund

HL Tau

6 years ago:

dust rings thrill the world

Credit: ALMA (ESO/NAOJ/NRAO)

Credit: Yen et al. 2019

6 years from now:

gaseous streamers mark the crucial link

Stars are born and embedded in large assemblies of gas

Star-disk systems form and are located in different environments provided by Giant Molecular Clouds (Size: 10 - 100 pc)

Credit: ALMA (ESO/NAOJ/NRAO)

Heterogeneous accretion implies late infall

Küffmeier et al.

2017

Observational indication: luminosity bursts

Late infall 

AB Aurigae

HD 100546

Credit: Grady+ 1999, Fukagawa+ 2004

Can (late) infall cause misalignment of inner and outer disk?

Credit: Ardila+ 2007

200 au

HD 142527

Credit: Avenhaus+ 2014

Extended arc-like structures can be induced by late infall

(Dullemond, Küffmeier, Goicovic+ 2019, Küffmeier, Goicovic & Dullemond 2020)

Possibility of "second-generation" disk

Shadows due to misaligned inner and outer disk

Credit: Marino+ 2015

Simulate cloudlet infall onto disk

AREPO, pure hydrodynamical

R_{\rm i,d}=50\, \rm au
\Sigma(r) = 170 \left(\frac{\rm g}{\rm cm}\right)^{2} \left( \frac{r}{1 \rm au} \right)^{-3/2}
M_{\rm cloudlet}(R_{\rm cloudlet}) = 0.01 {\rm M}_{\odot} \left( \frac{R_{\rm cloudlet}}{5000 \rm au}\right)^{2.3}
R_{\rm cloudlet} = 887\, \rm au

isothermal gas

vary infalling angle

\alpha = 0^{\circ} (35^{\circ}, 60^{\circ}, 90^{\circ})
b = 1774\, \rm au

vary rotation (prograde, retrograde)

Küffmeier, Dullemond, Reißl, Goicovic submitted

M_{*}=2.5\, \mathrm{M}_{\odot}

Outer disk forms around inner disk

Küffmeier+ subm

consistent with star formation simulations by Bate '18

Prograde vs. retrograde infall

Retrograde infall causes:

  • counter-rotating inner and outer disk 
  • shrinking of inner disk
  • enhanced accretion
  • larger and deeper gap between disks

see also Vorobyov+ 2016

Effect of infall angle on disk

Formation of misaligned configuration

Observable as shadows in outer disk

Disk evolution: eccentricity

prograde, 0°

Light to dark: retrograde infall with increasing inclination

  • mild eccentricity in inner disk (up to ~0.1)

inner

outer

  • larger eccentricities in outer disk (0.2 to 0.4)

Infall triggers:

=> probably measurable with CO channel maps:

a test of infall scenario

Disclaimer:

We are not saying that all shadows are due to misaligned infall!

In some cases shadows have already been well explained by external companions and/or inner planets (e.g.: HD 100453 Gonzalez+ '20/Nealon+ '20 or work by Zhu '19 on planet-induced misalignment)  

Infall mechanism in perspective

But we need to think out of the disk:

significant fraction of final mass might accrete later through inflow

(Pelkonen et al. 2020)

Pineda et al. 2020; see also [BHB2007] 1 (Alves et al. 2020)

Küffmeier et al. 2019

Zoom-in on embedded protostellar multiple

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

Take-away points

In infall-induced misaligned systems, the outer disk is expected to have higher eccentricity than the inner disk.

Retrograde infall can cause counter-rotating disks, shrinking of inner disk, formation of gaps (>10 AU) and enhanced accretion.

TBC: zoom-in simulations to consistently account for replenishment of disks through streamers 

WIP: study synthetic observations of infall-induced shadows

RGB image of misaligned system forming from infall with 60°

blue (1.66 micron), green (53 micron), red (870 micron); Credit: S. Reißl