Unveiling high-mass star formation with ALMA's longest baselines

Data: 
25/03/2019 - 14:00 - 15:00
Local: 
Auditório "Prof. Dr. Paulo Benevides Soares", Bloco G

Unveiling high-mass star formation with ALMA's longest baselines

Ciriaco Goddi

Radboud University

 

Understanding the formation of massive stars is one of the unsolved problems in modern astronomy.  The main difficulty is that the intense radiation from the high-luminosity stars and the thermal pressure from the resulting ionized gas (both insignificant for low-mass stars) may be able to reverse the accretion flow and prevent the star from accreting fresh material.
Such feedback effects can naturally be mitigated if accretion proceeds through discs, which is the established mechanism to form sun-like stars.  However, recent 3D MHD simulations have shown that accretion on 1000 au scales is through filaments rather than a large disc. This theoretical prediction has never been confirmed via observations owing to the poor linear resolution of previous studies (>1000 au).
Here we present the first observational evidence that mass assembly in young high-mass stars forming in protoclusters is predominantly asymmetric and disordered. We used ALMA longest baselines to observe the innermost regions around three deeply embedded high-mass protostars in the high-mass star formation complex W51, with very high spatial resolution (~100 au). We identified multiple massive (several solar masses), warm (50-150 Kelvin) filamentary streamers pointing onto the central sources, which we interpret as multi-directional accretion channels. These structures inhibit the formation of a large, steady disc.
While  our finding contrasts with the simplified classic paradigm of an ordered (and stable) disc/jet system  and provides an experimental confirmation of a  multi-directional and unsteady accretion model for massive star formation,  the identification of fast  collimated outflows in the three observed systems indicates that compact discs may be present (with upper limits on their radii of <~ 100 AU). While W51 is too far (5.4 kpc) to resolve such compact discs, even with the ALMA longest baselines, I will show a good example of a disc/jet system associated a massive YSO in the closest high-mass star forming region.