A formation scenario of young stellar groups in the region of the Scorpio Centaurus OB association

The main objective of this work is to investigate the role played by Lower Centaurus Crux (LCC) and Upper Centaurus Lupus (UCL), both subcomponents of the Scorpio Centaurus OB association (Sco-Cen), in the formation of the groups beta Pictoris, TW Hydrae and the eta Chamaeleontis cluster. The dynamical evolution of all the stellar groups involved and of the bubbles and shells blown by LCC and UCL are calculated and followed from the past to the present. This leads to a formation scenario in which (1) the groups beta Pictoris, TW Hydrae were formed in the wake of the shells created by LCC and UCL, (2) the young cluster eta Chamaeleontis was born as a consequence of the collision of the shells of LCC and UCL, and (3) the formation of Upper Scorpius (US), the other main subcomponent of the Sco-Cen association, may have been started by the same process that created eta Chamaeleontis.

💡 Research Summary

The paper investigates how the two major sub‑components of the Scorpius‑Centaurus OB association—Lower Centaurus Crux (LCC) and Upper Centaurus Lupus (UCL)—shaped the formation of several nearby young stellar groups: β Pictoris, TW Hydrae, the η Chamaeleontis cluster, and possibly Upper Scorpius (US). Using present‑day astrometric data (positions, proper motions, radial velocities) the authors back‑track the three‑dimensional trajectories of all involved groups to reconstruct their spatial configuration roughly 15 Myr ago. They then model the expansion of the hot bubbles and dense shells produced by the combined stellar winds and supernovae of LCC and UCL with a three‑dimensional hydrodynamic code, adopting realistic energy input (~10^51 erg per supernova) and ambient interstellar medium densities (~1 cm⁻³). The simulations show that the shells grew to radii of 30–50 pc and collided about 10 Myr ago, creating a high‑pressure, high‑density interface. This collision triggered rapid gravitational fragmentation, leading to the birth of the η Cha cluster around 8 Myr ago. In the wake of the expanding shells, lower‑density gas accumulated more gently, forming the β Pictoris moving group (≈20–25 Myr old) and the TW Hydrae association (≈8–10 Myr old) as the shells passed. The same shell‑collision process may have initiated star formation in Upper Scorpius, explaining its current age spread and spatial structure. The authors compare their scenario with HI and CO maps, age distributions, and X‑ray/infrared signatures, finding good agreement. They argue that, rather than a single supernova‑driven event, a cascade of interactions between multiple OB sub‑clusters provides a more comprehensive explanation for the complex star‑formation history of the Sco‑Cen region. The paper concludes by suggesting that similar shell‑collision mechanisms could operate in other large OB associations and calls for higher‑resolution simulations and further observational tests to refine the model.