Young star eats its way out of its cloud

Velocity map of hydrogen and sulphur in the small dark interstellar cloud B335. The shocks in the outflows (Herbig-Haro objects) are seen in unprecedented detail and six new shocks are discovered in this image. Credit: Magnus Gålfalk.

New observations done by Magnus Gålfalk and Göran Olofsson at Stockholm Observatory give the most detailed picture yet of Barnard 335 (B335), a well-known, very small dark interstellar cloud, a so called globule, in the constellation Aquila, forming only one or a few stars at its centre.

When stars are formed they go through a phase with simultaneous infall and outflow of gas onto and from the star. These flows are related in that the matter, that is accreted onto the star in a disk shape around its equator, is partially thrown out from its magnetic poles. The study, which is presented in a new article by Gålfalk et al., aims to map the outflows of hydrogen (H and H₂) and sulphur from this system. Due to the isolation, this is ideal for a case study of star formation since there is no confusion with other stars forming nearby. Such nearby star formation would otherwise produce mixed outflows from several stars.

- Our new observations are the deepest yet of B335 and reveal six new shocks (Herbig-Haro objects) in the outflows - only three such objects were known before this study. We also discovered at least 15 new shocks in molecular hydrogen. Since the cloud is very compact and the outflows create holes, one could think of it as the star eating its way out of its cloud, says Magnus Gålfalk.

By combining the new observations with images taken 9 and 15 years ago (H₂ and H, respectively) a velocity map for the outflows in B335 was produced. Two outflows were seen, suggesting that there may be a binary star forming in the centre of the globule, giving rise to two outflow axes. For one of the Herbig-Haro objects (called HH 119 A, having the shape of a bow shock) evidence for rapid expansion during the last 15 years was found.