Scorpius–Centaurus association

{{Short description|Nearest OB association to Earth}}

File:Sco-CenMap.png

File:Regioni_celesti_scelte_-_OB2.png half of the galactic plane, with Sco-Cen on the left]]

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) and its distance is about 130 parsecs or 420 light-years.{{cite journal|arxiv=2006.14649|doi=10.1007/s10509-020-03827-0|title=Distance scale for high-luminosity stars in OB associations and in field with Gaia DR2. Spurious systematic motions|year=2020|last1=Melnik|first1=A. M.|last2=Dambis|first2=A. K.|journal=Astrophysics and Space Science|volume=365|issue=7|page=112|bibcode=2020Ap&SS.365..112M|s2cid=220128144}} 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.{{citation | last1=Rizzuto | first1=Aaron | last2=Ireland| first2=Michael | last3=Robertson | first3=J. G. | title=Multidimensional Bayesian membership analysis of the Sco OB2 moving group | journal=Monthly Notices of the Royal Astronomical Society |date=October 2011 | volume=416 | issue=4 | pages=3108–17 | doi=10.1111/j.1365-2966.2011.19256.x | doi-access=free | bibcode=2011MNRAS.416.3108R | arxiv=1106.2857 | s2cid=54510608 | postscript=. }}

The Sco–Cen subgroups range in age from 11 million years (Upper Scorpius){{Cite journal|author=Mark J. Pecaut|author2=Eric E. Mamajek|author3=Eric J. Bubar|name-list-style=amp|date=February 2012|title=A Revised Age for Upper Scorpius and the Star Formation History among the F-type Members of the Scorpius–Centaurus OB Association|journal=Astrophysical Journal|volume=746|issue=2|pages=154|arxiv = 1112.1695 |bibcode = 2012ApJ...746..154P |doi = 10.1088/0004-637X/746/2/154 |s2cid=118461108}} to roughly 15 million years (Upper Centaurus–Lupus and Lower Centaurus–Crux). Many of the bright stars in the constellations 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.{{cite journal|title=The Nearest OB Association: Scorpius-Centaurus (Sco OB2)|author=Preibisch, T.|author2=Mamajek, E.|date=2009|journal=Handbook of Star-Forming Regions|volume=2|pages=0|bibcode=2008hsf2.book..235P|arxiv=0809.0407}} 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),

{{cite journal| title=Exploring the Full Stellar Population of the Upper Scorpius OB Association| author=Preibisch, T.| display-authors= etal|journal=Astronomical Journal|volume=124| issue=1|pages=404–416|bibcode=2002AJ....124..404P| doi=10.1086/341174| date=2002| doi-access=}} and the total stellar population in each of the three subgroups is probably of the order 1000–2000.{{cite journal|bibcode=2002AJ....124.1670M|author=Mamajek, E.E.|author2=Meyer, M.R.|author3=Liebert, James |name-list-style=amp|date=2002|journal=Astronomical Journal|volume=124|issue=3|pages=1670–1694|title=Post-T Tauri Stars in the Nearest OB Association|doi=10.1086/341952|arxiv = astro-ph/0205417 |s2cid=16855894}}

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 Chamaeleontis group, ~7 million-year-old Eta Chamaeleontis moving group, ~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,{{cite journal| title=Astrometric radial velocities. III. Hipparcos measurements of nearby star clusters and associations|author=Madsen, S.|display-authors= etal|date=2002 |journal=Astronomy & Astrophysics|volume=381| issue=2|pages=446–463|bibcode=2002A&A...381..446M| doi=10.1051/0004-6361:20011458|arxiv = astro-ph/0110617 |s2cid=17596452}} 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,{{cite journal| date=1992| bibcode=1992A&A...262..258D|author=de Geus, E.J.| title=Interaction of Stars and Interstellar Matter in Scorpio Centaurus| journal=Astronomy & Astrophysics|volume=262|pages=258–270}} 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{{cite journal|year=2016|title=Time-resolved 2-million-year-old supernova activity discovered in Earth's microfossil record|journal=Proceedings of the National Academy of Sciences|volume=113|issue=33|pages=9232–9237|doi=10.1073/pnas.1601040113|issn=0027-8424|last1=Ludwig|first1=Peter|display-authors=etal|pmid=27503888|pmc=4995991|arxiv=1710.09573|bibcode=2016PNAS..113.9232L|doi-access=free}} 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,{{cite journal| date=2005| bibcode=2005ApJ...621..902F| author=Fields, Brian D.| author2=Hochmuth, Kathrin A.| author3=Ellis, John| title=Deep-Ocean Crusts as Telescopes: Using Live Radioisotopes to Probe Supernova Nucleosynthesis| journal=Astrophys. J.| volume=621| issue=2| pages=902–07| doi=10.1086/427797|arxiv = astro-ph/0410525 | s2cid=17932224}} causing the Pliocene–Pleistocene boundary marine extinction.{{cite journal| date=2005| author=Benítez, N.| author2=Maíz-Apellániz, J.| author3=Canelles M.| title=Evidence for nearby supernova explosions| journal=Phys. Rev. Lett.| volume=88| issue=8| pages=081101| doi=10.1103/physrevlett.88.081101| pmid=11863949|arxiv = astro-ph/0201018 |bibcode = 2002PhRvL..88h1101B | s2cid=41229823}} 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.{{Cite journal|last=Cockell|first=CS|date=1999|title=Crises and extinction in the fossil record—A role for ultraviolet radiation?|journal=Paleobiology|volume=25|issue=2|pages=212–225|doi=10.1017/S0094837300026518|bibcode=1999Pbio...25..212C |s2cid=132108580 }}

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.{{cite journal |title=Interstellar 60Fe in Antarctica |volume = 123|issue = 7|pages = 072701|first1=D. |last1=Koll |first2=al. |last2=et. |journal=Physical Review Letters |year=2019 |doi=10.1103/PhysRevLett.123.072701|pmid = 31491090|bibcode = 2019PhRvL.123g2701K|s2cid = 201868513|hdl=1885/298253|hdl-access=free}}

File:OrionSpurInner.png, with major stellar associations (yellow), nebulae (red) and dark nebulae (grey) coreward from the Local Bubble with Sco-Cen.]]

In December 2021, around 70 new rogue planets were discovered in the Upper Scorpius association.{{cite web | title = ESO telescopes help uncover largest group of rogue planets yet | url = https://www.eso.org/public/news/eso2120/ | publisher = European Southern Observatory | date = 22 December 2021 | access-date = 22 December 2021}} See also attached [https://www.eso.org/public/archives/releases/sciencepapers/eso2120/eso2120a_en.pdf research paper].

The subgroups of the Scorpius–Centaurus association contains the youngest{{Cite web |title=Planetary Systems |url=https://exoplanetarchive.ipac.caltech.edu/cgi-bin/TblView/nph-tblView?app=ExoTbls&config=PS |access-date=2022-09-12 |website=exoplanetarchive.ipac.caltech.edu |quote=as of September 2022}} transiting exoplanets: K2-33 b (11 Myrs),{{Cite journal |last1=Mann |first1=Andrew W. |last2=Newton |first2=Elisabeth R. |last3=Rizzuto |first3=Aaron C. |last4=Irwin |first4=Jonathan |last5=Feiden |first5=Gregory A. |last6=Gaidos |first6=Eric |last7=Mace |first7=Gregory N. |last8=Kraus |first8=Adam L. |last9=James |first9=David J. |last10=Ansdell |first10=Megan |last11=Charbonneau |first11=David |last12=Covey |first12=Kevin R. |last13=Ireland |first13=Michael J. |last14=Jaffe |first14=Daniel T. |last15=Johnson |first15=Marshall C. |date=2016-09-01 |title=Zodiacal Exoplanets in Time (ZEIT). III. A Short-period Planet Orbiting a Pre-main-sequence Star in the Upper Scorpius OB Association |journal=The Astronomical Journal |volume=152 |issue=3 |pages=61 |doi=10.3847/0004-6256/152/3/61 |issn=0004-6256|arxiv=1604.06165 |bibcode=2016AJ....152...61M |s2cid=6552081 |doi-access=free }} TOI-1227 b (11 Myrs){{Cite journal |last1=Mann |first1=Andrew W. |last2=Wood |first2=Mackenna L. |last3=Schmidt |first3=Stephen P. |last4=Barber |first4=Madyson G. |last5=Owen |first5=James E. |last6=Tofflemire |first6=Benjamin M. |last7=Newton |first7=Elisabeth R. |last8=Mamajek |first8=Eric E. |last9=Bush |first9=Jonathan L. |last10=Mace |first10=Gregory N. |last11=Kraus |first11=Adam L. |last12=Thao |first12=Pa Chia |last13=Vanderburg |first13=Andrew |last14=Llama |first14=Joe |last15=Johns-Krull |first15=Christopher M. |date=2022-04-01 |title=TESS Hunt for Young and Maturing Exoplanets (THYME). VI. An 11 Myr Giant Planet Transiting a Very-low-mass Star in Lower Centaurus Crux |journal=The Astronomical Journal |volume=163 |issue=4 |pages=156 |doi=10.3847/1538-3881/ac511d |arxiv=2110.09531 |bibcode=2022AJ....163..156M |issn=0004-6256|doi-access=free }} and HIP 67522 b (17 Myrs).{{Cite journal |last1=Rizzuto |first1=Aaron C. |last2=Newton |first2=Elisabeth R. |last3=Mann |first3=Andrew W. |last4=Tofflemire |first4=Benjamin M. |last5=Vanderburg |first5=Andrew |last6=Kraus |first6=Adam L. |last7=Wood |first7=Mackenna L. |last8=Quinn |first8=Samuel N. |last9=Zhou |first9=George |last10=Thao |first10=Pa Chia |last11=Law |first11=Nicholas M. |last12=Ziegler |first12=Carl |last13=Briceño |first13=César |date=2020-07-01 |title=TESS Hunt for Young and Maturing Exoplanets (THYME). II. A 17 Myr Old Transiting Hot Jupiter in the Sco-Cen Association |journal=The Astronomical Journal |volume=160 |issue=1 |pages=33 |doi=10.3847/1538-3881/ab94b7 |arxiv=2005.00013 |bibcode=2020AJ....160...33R |issn=0004-6256|doi-access=free }} It also contains directly imaged exoplanets such as UScoCTIO 108 b and the PDS 70 system.{{Cite journal |last1=Keppler |first1=M. |last2=Benisty |first2=M. |last3=Müller |first3=A. |last4=Henning |first4=Th. |last5=van Boekel |first5=R. |last6=Cantalloube |first6=F. |last7=Ginski |first7=C. |last8=van Holstein |first8=R. G. |last9=Maire |first9=A. -L. |last10=Pohl |first10=A. |last11=Samland |first11=M. |last12=Avenhaus |first12=H. |last13=Baudino |first13=J. -L. |last14=Boccaletti |first14=A. |last15=de Boer |first15=J. |date=2018-09-01 |title=Discovery of a planetary-mass companion within the gap of the transition disk around PDS 70 |journal=Astronomy and Astrophysics |volume=617 |pages=A44 |doi=10.1051/0004-6361/201832957 |arxiv=1806.11568 |bibcode=2018A&A...617A..44K |issn=0004-6361|doi-access=free }}