Scorpius-Centaurus Association
Encyclopedia
The Scorpius-Centaurus Association (sometimes called Sco-Cen or Sco OB2) is the nearest
OB Association to the Sun
. This stellar association is composed of three subgroups (Upper Scorpius,
Upper Centaurus-Lupus, and Lower Centaurus-Crux), whose mean distances range from
380 to 470 light years
.
The Sco-Cen subgroups range in age from 5 million years (Upper Scorpius) to roughly 15 million years (Upper Centaurus-Lupus and Lower Centaurus-Crux). Many of the bright star
s in the constellation
s Scorpius
, Lupus
, Centaurus
, and Crux
are members of the Sco-Cen association, including Antares
(the most massive member of Upper Scorpius), and most of the stars in the Southern Cross. Hundreds of star
s have been identified as members of Sco-Cen, with masses ranging from roughly 15 solar mass
es (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.
The Sco-Cen OB association appears to be the most pronounced part of a large complex of recent (<20 million years) and ongoing star-formation. The complex contains several star-forming molecular clouds in Sco-Cen's immediate vicinity—the Rho Oph
, Pipe Nebula
, Barnard 68
, Chamaeleon
, Lupus
, Corona Australis
, and Coalsack cloud complexes (all at distances of ~120-200 parsecs), and several less populous, young stellar groups on the periphery of Sco-Cen, including the ~3-5 million-year-old epsilon Cha group, ~7 million-year-old eta Chamaeleontis cluster (also called Mamajek 1), ~8 million-year-old TW Hydrae association
, ~12 million-year-old Beta Pictoris moving group
, and possibly the ~30-50 million-year-old IC 2602
open cluster.
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 superbubble
s around the group, including the Loop I Bubble
.
To explain the presence of radioactive 60Fe in deep ocean ferromanganese crusts, 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.
OB Association to the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. This stellar association is composed of three subgroups (Upper Scorpius,
Upper Centaurus-Lupus, and Lower Centaurus-Crux), whose mean distances range from
380 to 470 light years
Light Years
Light Years is the seventh studio album by Australian recording artist Kylie Minogue. It was released on 25 September 2000 by Parlophone and Mushroom Records. The album's style was indicative of her return to "mainstream pop dance tunes"....
.
The Sco-Cen subgroups range in age from 5 million years (Upper Scorpius) to roughly 15 million years (Upper Centaurus-Lupus and Lower Centaurus-Crux). Many of the bright star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
s Scorpius
Scorpius
Scorpius, sometimes known as Scorpio, is one of the constellations of the zodiac. Its name is Latin for scorpion, and its symbol is . It lies between Libra to the west and Sagittarius to the east...
, Lupus
Lupus (constellation)
Lupus is a constellation in the southern sky. Its name is Latin for wolf. Lupus was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations...
, Centaurus
Centaurus
Centaurus is a bright constellation in the southern sky. One of the largest constellations, Centaurus was included among the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations.-Stars:...
, and Crux
Crux
Crux is the smallest of the 88 modern constellations, but is one of the most distinctive. Its name is Latin for cross, and it is dominated by a cross-shaped asterism that is commonly known as the Southern Cross.-Visibility:...
are members of the Sco-Cen association, including Antares
Antares
Antares is a red supergiant star in the Milky Way galaxy and the sixteenth brightest star in the nighttime sky . Along with Aldebaran, Spica, and Regulus it is one of the four brightest stars near the ecliptic...
(the most massive member of Upper Scorpius), and most of the stars in the Southern Cross. Hundreds of star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s have been identified as members of Sco-Cen, with masses ranging from roughly 15 solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
es (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.
The Sco-Cen OB association appears to be the most pronounced part of a large complex of recent (<20 million years) and ongoing star-formation. The complex contains several star-forming molecular clouds in Sco-Cen's immediate vicinity—the Rho Oph
Rho Ophiuchi cloud complex
The Rho Ophiuchi cloud complex is a dark nebula of gas and dust that is located 1° south of the star ρ Ophiuchi of the constellation Ophiuchus. At an estimated distance of , this cloud is one of the closest star-forming regions to the Solar System....
, Pipe Nebula
Pipe Nebula
The Pipe Nebula is a dark nebula in the Ophiuchus constellation. It is a large but readily apparent pipe shaped dust lane that obscures the Milky Way star clouds behind it...
, Barnard 68
Barnard 68
Barnard 68 is a molecular cloud, dark absorption nebula or Bok globule, towards the southern constellation Ophiuchus and well within our own galaxy at a distance of about 500 light-years, so close that not a single star can be seen between it and the Sun. American astronomer Edward Emerson Barnard...
, Chamaeleon
Chamaeleon
Chamaeleon is a small constellation in the southern sky. It is named after the chameleon, a form of lizard. It was first defined in the sixteenth century.-History:...
, Lupus
Lupus (constellation)
Lupus is a constellation in the southern sky. Its name is Latin for wolf. Lupus was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations...
, Corona Australis
Corona Australis
Corona Australis or Corona Austrina is a constellation. Its name means "southern crown", and it contrasts with Corona Borealis, the northern crown...
, and Coalsack cloud complexes (all at distances of ~120-200 parsecs), and several less populous, young stellar groups on the periphery of Sco-Cen, including the ~3-5 million-year-old epsilon Cha group, ~7 million-year-old eta Chamaeleontis cluster (also called Mamajek 1), ~8 million-year-old TW Hydrae association
TW Hydrae association
The TW Hydrae association is a group of approximately thirty very young stars located 50 parsecs from Earth that share a common motion and appear to all be roughly the same age, 5-10 million years old...
, ~12 million-year-old Beta Pictoris moving group
Beta Pictoris Moving Group
The Beta Pictoris Moving Group is a young moving group of stars located relatively near Earth. A moving group, in astronomy, is a group of stars that share a common motion through space as well as a common origin...
, and possibly the ~30-50 million-year-old IC 2602
IC 2602
IC 2602 is an open cluster in the constellation Carina. It was discovered by Abbe Lacaille in 1751 from South Africa. The cluster is at a distance of about 479 light-years away from Earth and can be seen with the naked eye...
open cluster.
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
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. 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 superbubble
Superbubble
Superbubble is the astronomical term used to describe a cavity hundreds of light years across filled with 106 K gas blown into the interstellar medium by multiple supernovae and stellar winds...
s around the group, including the Loop I Bubble
Loop I Bubble
The Loop I Bubble is a cavity in the interstellar medium of the Orion Arm of the Milky Way. From our Sun's point of view, it is situated towards the Galactic Center of the Milky Way galaxy. Two conspicuous tunnels connect the Local Bubble with the Loop I cavity .The Loop I Bubble is located...
.
To explain the presence of radioactive 60Fe in deep ocean ferromanganese crusts, it has been hypothesized that a nearby supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
, possibly a member of Sco-Cen, exploded in the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
's vicinity roughly 3 million years ago.