Unveiling the Milky Way with a Gaia DR3 census of OB-type stars within 2 kpc. I. Tracing local Galactic structure, massive star-forming regions and core-collapse supernova progenitors

Abstract

Abstract O- and B-type stars are young and hot, thereby serving as vital tracers of the star formation and spiral arm structure of the Milky Way. At the dusk of the Gaia DR3 era, a high-confidence and accurate catalogue appears timely. We have characterized 105,971 OB-type stars (Teff > 10,000 K) within 2 kpc from the Sun, using an astro-photometric Bayesian inference tool. Our map unveils a complex view of the young stellar populations across the thin disk, with prominent large-scale features such as the Cepheus Spur, the Giant Oval Cavity, and a segment the Sagittarius-Carina arm all visible. Their inhomogeneous spatial distribution implies that massive star formation has taken place clustered across a few highly concentrated regions. We find a correlation between the overdensities of OB-type stars and young open clusters, and attribute departure from it to extinction effects. We identify 4200 stars as model-dependent core-collapse supernova (ccSN) or direct-collapse black hole (BH) progenitor candidates, including 6 ccSN progenitor candidates within 125 pc – the maximum radius within which a ccSN explosion could be harmful to Earth’s biosphere – but our analysis suggests none of them exploding within the next 5 Myrs. Finally, we anticipate more evolved OB-type stars to collapse to form BHs within the next 1 Myr than ccSN progenitors will explode, despite the former’s much scarcer number. A possible interpretation is a recent star formation burst in the local Milky Way, consistent with overdensities of ccSN progenitor candidates in Cyg OB2 and the Sagittarius-Carina arm.