Powerful jets and outflows are launched from the protostellar disks around newborn stars. These outflows carry enough mass and momentum to transform the structure of their parent molecular cloud and to potentially control star formation itself. Despite their importance, we have not been able to fully quantify the impact of jets and outflows during the formation of a star cluster. The main problem lies in limited computing power. We would have to resolve the magnetic jet-launching mechanism close to the protostar and at the same time follow the evolution of a parsec-size cloud for a million years. Current computer power and codes fall orders of magnitude short of achieving this. In order to overcome this problem, we implement a subgrid-scale (SGS) model for launching jets and outflows, which demonstrably converges and reproduces the mass, linear and angular momentum transfer, and the speed of real jets, with ~ 1000 times lower resolution than would be required without SGS model. We apply the new SGS model to turbulent, magnetized star cluster formation and show that jets and outflows (1) eject about 1/4 of their parent molecular clump in high-speed jets, quickly reaching distances of more than a parsec, (2) reduce the star formation rate by about a factor of two, and (3) lead to the formation of ~ 1.5 times as many stars compared to the no-outflow case. Most importantly, we find that jets and outflows reduce the average star mass by a factor of ~ 3 and may thus be essential for understanding the characteristic mass of the stellar initial mass function.
This movie shows the density structure perpendicular to the disk midplane of a collapsing, rotating cloud core, forming a single star in the center and driving a bipolar outflow. The left and middle panels show runs without subgrid-scale (SGS) model at low and high resolution, respectively. The right panel shows the same as the low-resolution run on the left, but with our new SGS model for launching jets and outflows activated. Using our SGS outflow model, we recover the fast, collimated, central jet component at low resolution. Note that the high-resolution run without SGS model, shown in the middle panel, is not fully converged and only recovers the jet component qualitatively. In contrast, the mass, momentum, angular momentum and speed of the outflow are converged when our SGS outflow model is used.
[ Federrath_outflow_sgs_model.mp4, 4.2MB high-res mp4 ]
This animation shows a comparison of star cluster formation without outflows (left-hand panel) and with outflow feedback included (right-hand panel). The star formation rate and efficiency are reduced by the outflows and the number of stars formed significantly increases. Both effects together lead to an average star mass that is reduced by a factor of ~ 3 when outflow feedback is included. This suggests that outflow and jet feedback are essential ingredients for understanding the stellar initial mass function.
[ Federrath_cluster_outflows.mp4, 9.7MB high-res mp4 ]
This movie shows the star cluster formation run with outflow feedback (left-hand panel). The outflowing gas emerging from the stars was marked and followed using a passive scalar tracer method in the right-hand panel. We see that the jets and outflows break out of their original cores and can affect distant parts of their parent molecular cloud.
[ Federrath_cluster_outflows_2.mp4, 8.9MB high-res mp4 ]
We thank M. Bate, B. Commercon, A. Cunningham, P. Girichidis, R. Klein, P. Kroupa, M. Krumholz, C. Matzner, C. McKee, S. Offner, R. Parkin, T. Peters, D. Price, R. Pudritz, and D. Seifried for stimulating discussions about jets and outflows, and for comments on the paper. CF acknowledges funding provided by the Australian Research Council's Discovery Projects (grant no. DP110102191). MS acknowledges kind support from Dieter Breitschwerdt (Dept. of Astronomy & Astrophysics, Technical University Berlin). RB acknowledges support from the DFG through the grants BA 3706/1-1, BA 3706/3-1, BA 3706/4-1 as well as support through the SFB 676. RSK acknowledges support from the Deutsche Forschungsgemeinschaft (DFG) via the SFB 881 (subproject B1, B2 and B5) "The Milky Way System", and the SPP (priority program) 1573 "Physics of the ISM". RSK also acknowledges support from the European Research Council under the European Community's Seventh Framework Programme (FP7/2007-2013) via the ERC Advanced Grant STARLIGHT (project number 339177). We thank for supercomputing time provided by the Leibniz Rechenzentrum and the Gauss Centre for Supercomputing (grant pr32lo and PRACE grant pr89mu) and by the Jülich Supercomputing Centre (grant hhd20). The software used in this work was in part developed by the DOE-supported Flash Center for Computational Science at the University of Chicago. This research was supported in part by the National Science Foundation under Grant No. NSF PHY11-25915 during CF's visit to the Kavli Institute for Theoretical Physics, where this work was completed.