MOBSTER - At the crossroads of stellar astrophysics in the upper HR Diagram

<p>Contrarily to low-mass stars, in which dynamo-generated surface magnetism is essentially ubiquitous, only about 10% of stars with radiative envelopes (O, B and A) exhibit detectable magnetic fields at their surfaces. Yet, this small magnetic subpopulation includes potential progenitors of exotic astronomical objects, such as high-mass stellar black holes (even at solar metallicity) and magnetars. Therefore, there is a strong motivation to learn more about the as-yet misunderstood formation of these stars, and what is currently lacking is a robust statistical basis to interpret their properties. In this talk, I will briefly review massive star magnetism and some of the critical gaps in knowledge that currently plague their study. I will then discuss the observational limitations that prevent us from learning more, and argue that all-sky broadband photometric missions such as the Transiting Exoplanet Survey Satellite (TESS) offer a valuable indirect method of addressing these limitations. Finally, I will present the MOBSTER (Magnetic OB[A] Stars with TESS: probing their Evolutionary and Rotational properties) collaboration, and highlight some of its early results, as well as offer a glimpse of the road that lies ahead.</p>