Scorpius–Centaurus association

The Scorpius–Centaurus association (also known as Sco–Cen or Sco OB2) is the closest OB association to the Solar System, composed of three subgroup (Upper Scorpius, Upper Centaurus–Lupus, and Lower Centaurus–Crux) located at a distance of 420 light-years (130 parsecs) from the Sun. Analysis using improved Hipparcos data has brought the number of known members to 436. The cluster shows a continuous spread of stars with no apparent need for subclassification.

The Sco–Cen subgroups range in age from 11 million years (Upper Scorpius) to roughly 15 million years (Upper Centaurus–Lupus and Lower Centaurus–Crux). Many of the bright stars in the constellations of Scorpius, Lupus, Centaurus, and Crux are in fact the brightest members of the Sco–Cen association, including the red supergiant star Antares (the most massive member of Upper Scorpius), and most of the stars in the Southern Cross. Hundreds of stars have been identified as members of Sco-Cen, with masses ranging from roughly 15 solar masses (Antares) down to below the hydrogen-burning limit (i.e. brown dwarfs), and the total stellar population in each of the three subgroups is probably of the order 1000–2000 and the total number of stars in the association exceeds 10,000.

The stellar members of the Sco–Cen association have convergent proper motions of approximately 0.02–0.04 arcseconds per year, indicative that the stars have nearly parallel velocity vectors, moving at about 20 km/s with respect to the Sun. The dispersion of the velocities within the subgroups are only of order 1–2 km/s, and the group is most likely gravitationally unbound. Several supernovae have exploded in Sco–Cen over the past 15 million years, leaving a network of expanding gas superbubbles around the group, including the Loop I Bubble.

To explain the presence of radioactive ⁶⁰Fe in deep ocean ferromanganese crusts and in biogenic magnetite crystals within Pacific Ocean sediments it has been hypothesized that a nearby supernova, possibly a member of Sco–Cen, exploded in the Sun's vicinity roughly 3 million years ago, causing the Pliocene–Pleistocene boundary marine extinction. However, other findings cite the distance at which this supernova occurred at more than 100 parsec, maintaining that it is not likely not to have contributed to this extinction through the mechanism of what is known as the ultra-violet B (UV-B) catastrophe. In 2019, researchers found interstellar iron in Antarctica which they relate to the Local Interstellar Cloud, which might have been formed near the Sco-Cen association.