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Mathematisch-Naturwissenschaftliche FakultätAstrophysik I.Physik

Fragmentation and accretion in massive star-forming cores

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  • Figure 1: In the first column are the gas column densities on a logarithmic scale, in the second column are the tracer column densities, and in the third one are the column densities of the tracers that will be and are within the sink accretion radius of the most massive sink (MMS) at all times. In the fourth column are zoom-ins of the third column. The column densities are centered around the MMS and the line of sight is in z-direction. Cyan-colored dots represent sink particles. One can see that the tracers are initially located on a larger region of the cloud, and that this "tracer cloud" gradually collapses towards the center. In the zoom-ins we can see streamer-like structures seemingly feed the MMS.
  • Figure 2: Considered are all tracers that will end up within the accretion radius of a sink. We show the distributions of radial distances between all those tracers and the corresponding sink at different times. Note that the y-axis is not normalized, since the amount of tracers is important. For the MMS most of the tracers are initially located further away from the sink, and at later times the majority of the tracers have not reached the sink. Thus, the MMS draws mass from a larger region of the cloud for a longer time. Lower-mass sinks draw most of the tracers from nearby and the majority of the tracers reach the sink at later times.

Nuray Ortaköse

The field of massive star formation continues to be riddled with unanswered questions. Two main theories on accretion have been debated in recent years: Competitive Accretion and Core Accretion. In Core Accretion a molecular cloud will fragment into cores with different masses. The high-mass stars are formed through the collapse of self-gravitating, dense cores. Thus, the final mass of the star is dependent on the core mass. In Competitive Accretion, the mass is accreted from a wider region of the clump, while never being in a phase of a gravitationally bound core. The clump feeds the central region where the forming stars compete for the mass and the most massive star forms at the bottom of the potential well.

In our work, we investigate the accretion and fragmentation process from the simulation of a high-mass star-forming collapsing cloud, by using the tracer particle data to retrieve the history of the gas evolution. Tracer particles (tracers) are mass-less particles, which follow the velocity field of the simulation. Sink particles are used to model proto-stellar objects. Initial conditions are a centrally peaked density profile and αvir<1. The considered feedback processes are ionizing radiation and radiation pressure. We find that the massive stars draw mass from a large mass reservoir, which exceeds the dense central region (See Fig.1 and Fig.2). This mass reservoir replenishes the central region, while the stars compete for the mass. Additionally, we see that massive stars also form outside the central region, showing that they are provided with their own mass reservoir while competing with the other stars. We conclude, that the accretion process is most likely competitive.