April 2026
Estimating ionization fractions in SILCC simulations (Lennart Buhlmann)
EVOLUTION OF HUBBLE WEDGES IN EPISODIC PROTOSTELLAR OUTFLOWS
During the early phase of star formation, protostars undergo short phases of high accretion rates. Such outbursts are observed in FU Orionis type stars (FUors), which experience a rapid increase in accretion rate, from ∼10−7M⊙yr−1 to ∼10−4M⊙yr−1, for a period of order 10 years.
Most, possibly all forming protostars launch fast bipolar outflows. The inference is that, during the collapse of the dense core, gravitational energy is converted into kinetic and magnetic energy, which then drives and collimates the outflow. Changes in the ejection rate, caused by sudden accretion events, lead to the formation of bullets and internal working surfaces, which are shocked layers between the fast ejecta and the gas in the outflow cavity. More evolved outflows break out of their parental core or cloud and form parsec-scale outflows, traced by chains of Herbig--Haro objects. In some cases these chains extend to over 10pc, e.g. HH 131 with an extent of 17pc.
We have developed a new episodic outflow model for the SPH code GANDALF, which mimics the accretion and ejection behaviour of FU Ori type stars (Stamatellos et al. 2012; Hubber et al. 2018; Rohde et al. 2019). We apply this model to simulations of star formation, invoking two types of initial conditions: spherically symmetric cores of 1.0M⊙ in solid-body rotation with ρ∝r−2 density profile, and spherically symmetric turbulent cores of 2.7M⊙ with density proportional to the density of a Bonnor-Ebert sphere.
For a wide range of model parameters, we find that episodic outflows lead to self-regulation of the ejected mass and momentum reducing the star formation efficiency by a factor of ∼0.6.
A common relation observed in protostellar outflows is a linear position-velocity (PV) relation, i.e. a `Hubble Law', in which the velocity of the outflowing gas increases linearly with distance from the source. Recent observations show that the PV diagram also exhibits so-called `Hubble Wedges' of high-velocity emission, caused by the bow shocks of individual outflow bullets. In our model, we are able to reproduce the `Hubble Wedges' as recently ejected outflow bullets. The outflow bullets then decelerate and align with the older bullets forming the well known `Hubble-Law' relation when they hit the leading shock front.
Monthly Highlights
March 2026
1D protostellar disk sub-grid model for star formation 3D MHD simulations (Anaïs Pauchet)
January 2026
Protostellar Outflows: From Simulations to Synthetic Observations (Taishi Ushirogi)
December 2025
Prestellar Core Formation in Colliding Gas Flows: Simulations and Synthetic Observations (Felix Rauprich)
November 2025
Measuring the Velocity Dispersion of the Warm Neutral Medium of the Milky Way at Galactic Scale using the Code FLASH (Wajdee Chayeb)
October 2025
Higher-order finite volume method for modelling shock waves in the interstellar medium (Mervin Yap)
June 2025
Simulating [CII] emission in high-redshift galaxies and their halos (Clarissa Immisch)
May 2025
Episodic Accretion onto Low Mass Protostars (Christian Riesop)
April 2025
Molecular cloud formation: Impact of metallicity, far-UV and CR heating using SILCC-Zoom simulations (Sanjit Pal)
March 2025
Modelling Protostellar Outflows in ISM Simulations (Michael Weis)
February 2025
Multi-band ray-tracing of ionizing photons (Sebastian Vider)
December 2024
Simulating the ISM and its processes (Sebastian Vider)