Editing Star formation (section)

==Low mass and high mass star formation==
[[File:Infrared Image of Dark Cloud in Aquila.jpg|thumb|Star-forming region [[Westerhout 40]] and the [[Serpens-Aquila Rift]]- cloud filaments containing new stars fill the region.<ref name=kuhn10>{{Cite journal| last = Kuhn | first = M. A. | display-authors = etal | year=2010 | title = A Chandra Observation of the Obscured Star-forming Complex W40 | journal = Astrophysical Journal | volume = 725 | issue=2 | pages = 2485–2506 | doi=10.1088/0004-637X/725/2/2485 | bibcode=2010ApJ...725.2485K|arxiv = 1010.5434 | s2cid = 119192761 }}</ref><ref name=andre10>{{Cite journal |last=André |first=Ph. |display-authors=etal |date=2010 |title= From filamentary clouds to prestellar cores to the stellar IMF: Initial highlights from the Herschel Gould Belt Survey |journal=Astronomy & Astrophysics |volume=518 |pages=L102 |doi=10.1051/0004-6361/201014666 |bibcode= 2010A&A...518L.102A|arxiv = 1005.2618 |s2cid=248768 }}</ref>
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Stars of different masses are thought to form by slightly different mechanisms.  The theory of low-mass star formation, which is well-supported by observation, suggests that low-mass stars form by the gravitational collapse of rotating density enhancements within molecular clouds.  As described above, the collapse of a rotating cloud of gas and dust leads to the formation of an accretion disk through which matter is channeled onto a central protostar.  For stars with masses higher than about {{Solar mass|8}}, however, the mechanism of star formation is not well understood.

Massive stars emit copious quantities of radiation which pushes against infalling material.  In the past, it was thought that this [[radiation pressure]] might be substantial enough to halt accretion onto the massive protostar and prevent the formation of stars with masses more than a few tens of solar masses.<ref>{{cite journal | author = M. G. Wolfire | author2 = J. P. Cassinelli | title = Conditions for the formation of massive stars | journal = Astrophysical Journal | date = 1987 | volume = 319 | issue = 1 | pages = 850–867 | bibcode = 1987ApJ...319..850W  | doi = 10.1086/165503| doi-access = free }}</ref> Recent theoretical work has shown that the production of a jet and outflow clears a cavity through which much of the radiation from a massive protostar can escape without hindering accretion through the disk and onto the protostar.<ref>{{cite journal | author = C. F. McKee | author2 = J. C. Tan | title = Massive star formation in 100,000 years from turbulent and pressurized molecular clouds | journal = Nature | date = 2002 | volume = 416 | issue = 6876 | pages = 59–61 | bibcode = 2002Natur.416...59M  | doi = 10.1038/416059a | pmid = 11882889|arxiv = astro-ph/0203071 | s2cid = 4330710 }}</ref><ref>{{cite journal | author = R. Banerjee | author2 = R. E. Pudritz | title = Massive star formation via high accretion rates and early disk-driven outflows | journal = Astrophysical Journal | date = 2007 | volume = 660 | issue = 1 | pages = 479–488 | bibcode = 2007ApJ...660..479B  | doi = 10.1086/512010|arxiv = astro-ph/0612674 | s2cid = 9769562 }}</ref> Present thinking is that massive stars may therefore be able to form by a mechanism similar to that by which low mass stars form.

There is mounting evidence that at least some massive protostars are indeed surrounded by accretion disks.<ref name=rab>{{Cite journal |last1=Burns |first1=R. A. |last2=Uno |first2=Y. |last3=Sakai |first3=N. |last4=Blanchard |first4=J. |last5=Rosli |first5=Z. |last6=Orosz |first6=G. |last7=Yonekura |first7=Y. |last8=Tanabe |first8=Y. |last9=Sugiyama |first9=K. |last10=Hirota |first10=T. |last11=Kim |first11=Kee-Tae |last12=Aberfelds |first12=A. |last13=Volvach |first13=A. E. |last14=Bartkiewicz |first14=A. |last15=Caratti o Garatti |first15=A. |date=May 2023 |title=A Keplerian disk with a four-arm spiral birthing an episodically accreting high-mass protostar |url=https://www.nature.com/articles/s41550-023-01899-w |journal=Nature Astronomy |language=en |volume=7 |issue=5 |pages=557–568 |doi=10.1038/s41550-023-01899-w |s2cid=257252773 |issn=2397-3366|arxiv=2304.14740 |bibcode=2023NatAs...7..557B }}</ref>  Disk accretion in high-mass protostars, similar to their low-mass counterparts, is expected to exhibit bursts of episodic accretion as a result of a gravitationally instability leading to clumpy and in-continuous accretion rates. Recent evidence of accretion bursts in high-mass protostars has indeed been confirmed observationally.<ref name=rab/><ref>{{Cite journal |last1=Caratti o Garatti |first1=A. |last2=Stecklum |first2=B. |last3=Garcia Lopez |first3=R. |last4=Eislöffel |first4=J. |last5=Ray |first5=T. P. |last6=Sanna |first6=A. |last7=Cesaroni |first7=R. |last8=Walmsley |first8=C. M. |last9=Oudmaijer |first9=R. D. |last10=de Wit |first10=W. J. |last11=Moscadelli |first11=L. |last12=Greiner |first12=J. |last13=Krabbe |first13=A. |last14=Fischer |first14=C. |last15=Klein |first15=R. |date=March 2017 |title=Disk-mediated accretion burst in a high-mass young stellar object |url=https://www.nature.com/articles/nphys3942 |journal=Nature Physics |language=en |volume=13 |issue=3 |pages=276–279 |doi=10.1038/nphys3942 |issn=1745-2481|arxiv=1704.02628 |bibcode=2017NatPh..13..276C }}</ref><ref>{{Cite journal |last1=Hunter |first1=T. R. |last2=Brogan |first2=C. L. |last3=MacLeod |first3=G. |last4=Cyganowski |first4=C. J. |last5=Chandler |first5=C. J. |last6=Chibueze |first6=J. O. |last7=Friesen |first7=R. |last8=Indebetouw |first8=R. |last9=Thesner |first9=C. |last10=Young |first10=K. H. |date=2017-03-15 |title=An Extraordinary Outburst in the Massive Protostellar System NGC 6334I-MM1: Quadrupling of the Millimeter Continuum |journal=The Astrophysical Journal |volume=837 |issue=2 |pages=L29 |doi=10.3847/2041-8213/aa5d0e |doi-access=free |issn=2041-8213|arxiv=1701.08637 |bibcode=2017ApJ...837L..29H }}</ref> Several other theories of massive star formation remain to be tested observationally.  Of these, perhaps the most prominent is the theory of competitive accretion, which suggests that massive protostars are "seeded" by low-mass protostars which compete with other protostars to draw in matter from the entire parent molecular cloud, instead of simply from a small local region.<ref>{{cite journal | author = I. A. Bonnell | author2 = M. R. Bate | author3 = C. J. Clarke| author4 = J. E. Pringle | title = Accretion and the stellar mass spectrum in small clusters | journal = Monthly Notices of the Royal Astronomical Society | date = 1997 | volume = 285 | issue = 1 | pages = 201–208 | bibcode = 1997MNRAS.285..201B | doi=10.1093/mnras/285.1.201| doi-access = free }}</ref><ref>{{cite journal | author = I. A. Bonnell | author2 = M. R. Bate | title = Star formation through gravitational collapse and competitive accretion | journal = Monthly Notices of the Royal Astronomical Society | date = 2006 | volume = 370 | issue = 1 | pages = 488–494 | bibcode = 2006MNRAS.370..488B | doi = 10.1111/j.1365-2966.2006.10495.x | doi-access = free |arxiv = astro-ph/0604615 | s2cid = 15652967 }}</ref>

Another theory of massive star formation suggests that massive stars may form by the coalescence of two or more stars of lower mass.<ref>{{cite journal | author = I. A. Bonnell | author2 = M. R. Bate | author3 = H. Zinnecker | title = On the formation of massive stars | journal = Monthly Notices of the Royal Astronomical Society | date = 1998 | volume = 298 | issue = 1 | pages = 93–102 | bibcode = 1998MNRAS.298...93B  | doi = 10.1046/j.1365-8711.1998.01590.x| doi-access = free |arxiv = astro-ph/9802332 | s2cid = 119346630 }}</ref>