2020-6-24

On the Birth of Massive Stars

Speaker: Kei Tanaka (ALMA project, NAOJ)

Abstract:

Massive stars play a lot of essential roles in a wide range of astrophysical settings throughout cosmic history, and thus it is crucial to understand how they form. Compared to low-mass star formation whose standard scenario has been established in the 1980s, research on massive star formation has been dramatically developing in recent years. In this talk, I will introduce our recent theoretical and observational studies on massive star formation. We developed the first model including multiple feedback processes, i.e., MHD disk wind, radiation pressure, photo-ionization, and stellar winds. Our model suggested that, unlike the conventional picture, the MHD disk wind is the dominant feedback rather than radiative feedback, even in the formation of very massive stars (>100Msun). Along with the theoretical works, we also conducted high-resolution ALMA observations to unveil massive protostars that are still deeply embedded in molecular clouds. Utilizing radiative transfer modeling, we measured the photo-evaporation rate from a 40Msun protostar as ~3e-5Msun/yr, which is consistent with our theoretical predictions. Moreover, we detected rich dynamical and chemical structures, such as the rotating envelopes/disks, synchrotron jets, and massive proto-binaries. One of the most exciting findings is that the refractory molecules, such as salt (NaCl), and silicon compounds (SiO, SiS), associated with massive protostellar disks at several hundred au. These “hot-disk” chemistry would have great potential for future research developing from the classic hot-core chemistry. Finally, to connect the present-day and the early universe, we will also discuss massive star formation at low-metallicity environments based on our new theoretical and observational studies.