Scorpius–Centaurus association
| Scorpius–Centaurus association | |
|---|---|
 Scorpius–Centaurus association | |
| Observation data (J2000 epoch) | |
| Constellation | Scorpius Lupus Centaurus Crux Musca |
| Right ascension | 16h 15m 0.00s |
| Declination | −24° 11′ 60.0″ |
| Mean distance | 420 ly (130 pc) |
| Radial velocity | −4.1 km/s |
| Physical characteristics | |
| Subgroups | Upper Scorpius, Upper Centaurus–Lupus, Lower Centaurus–Crux |
| Other designations | Sco–Cen, Sco OB2 |
The Scorpius–Centaurus association (also known as Sco–Cen or Sco OB2) is the closest OB association to the Solar System, composed of three subgroups (Upper Scorpius, Upper Centaurus–Lupus, and Lower Centaurus–Crux) and 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. 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, indicating 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 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 and leaving radioactive 60Fe in deep ocean ferromanganese crusts and in biogenic magnetite crystals within Pacific Ocean sediments. 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 an 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.