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Star formation

Star formation is the process by which dense regions within molecular clouds in interstellar space, sometimes referred to as "stellar nurseries" or "star-forming regions", collapse and form stars. As a branch of astronomy, star formation includes the study of the interstellar medium (ISM) and giant molecular clouds (GMC) as precursors to the star formation process, and the study of protostars and young stellar objects as its immediate products. It is closely related to planet formation, another branch of astronomy. Star formation theory, as well as accounting for the formation of a single star, must also account for the statistics of binary stars and the initial mass function. Most stars do not form in isolation but as part of a group of stars referred as star clusters or stellar associations.

Contents

Hubble telescope image known as Pillars of Creation, where stars are forming in the Eagle Nebula

Interstellar clouds

The W51 nebula in Aquila - one of the largest star factories in the Milky Way (August 25, 2020)

A spiral galaxy like the Milky Way contains stars, stellar remnants, and a diffuse interstellar medium (ISM) of gas and dust. The interstellar medium consists of 10−4 to 106 particles per cm3 and is typically composed of roughly 70% hydrogen by mass, with most of the remaining gas consisting of helium. This medium has been chemically enriched by trace amounts of heavier elements that were produced and ejected from stars via the fusion of helium as they passed beyond the end of their main sequence lifetime. Higher density regions of the interstellar medium form clouds, or diffuse nebulae, where star formation takes place. In contrast to spirals, an elliptical galaxy loses the cold component of its interstellar medium within roughly a billion years, which hinders the galaxy from forming diffuse nebulae except through mergers with other galaxies.

In the dense nebulae where stars are produced, much of the hydrogen is in the molecular (H2) form, so these nebulae are called molecular clouds. Herschel Space Observatory have revealed that filaments are truly ubiquitous in the molecular cloud. Dense molecular filaments, which are central to the star formation process, will fragment into gravitationally bound cores, most of which will evolve into stars. Continuous accretion of gas, geometrical bending, and magnetic fields may control the detailed fragmentation manner of the filaments. In supercritical filaments observations have revealed quasi-periodic chains of dense cores with spacing comparable to the filament inner width, and includes embedded protostars with outflows. Observations indicate that the coldest clouds tend to form low-mass stars, observed first in the infrared inside the clouds, then in visible light at their surface when the clouds dissipate, while giant molecular clouds, which are generally warmer, produce stars of all masses. These giant molecular clouds have typical densities of 100 particles per cm3, diameters of 100 light-years (9.5×1014 km), masses of up to 6 million solar masses (M), and an average interior temperature of 10 K. About half the total mass of the galactic ISM is found in molecular clouds and in the Milky Way there are an estimated 6,000 molecular clouds, each with more than 100,000 M. The nearest nebula to the Sun where massive stars are being formed is the Orion Nebula, 1,300 ly (1.2×1016 km) away. However, lower mass star formation is occurring about 400–450 light years distant in the ρ Ophiuchi cloud complex.

A more compact site of star formation is the opaque clouds of dense gas and dust known as Bok globules, so named after the astronomer Bart Bok. These can form in association with collapsing molecular clouds or possibly independently. The Bok globules are typically up to a light year across and contain a few solar masses. They can be observed as dark clouds silhouetted against bright emission nebulae or background stars. Over half the known Bok globules have been found to contain newly forming stars.

Assembly of galaxy in early Universe.

Cloud collapse

An interstellar cloud of gas will remain in hydrostatic equilibrium as long as the kinetic energy of the gas pressure is in balance with the potential energy of the internal gravitational force. Mathematically this is expressed using the virial theorem, which states that, to maintain equilibrium, the gravitational potential energy must equal twice the internal thermal energy. If a cloud is massive enough that the gas pressure is insufficient to support it, the cloud will undergo gravitational collapse. The mass above which a cloud will undergo such collapse is called the Jeans mass. The Jeans mass depends on the temperature and density of the cloud, but is typically thousands to tens of thousands of solar masses. During cloud collapse dozens to tens of thousands of stars form more or less simultaneously which is observable in so-called embedded clusters. The end product of a core collapse is an open cluster of stars.

ALMA observations of the Orion Nebula complex provide insights into explosions at star birth.

In triggered star formation, one of several events might occur to compress a molecular cloud and initiate its gravitational collapse. Molecular clouds may collide with each other, or a nearby supernova explosion can be a trigger, sending shocked matter into the cloud at very high speeds. (The resulting new stars may themselves soon produce supernovae, producing self-propagating star formation.) Alternatively, galactic collisions can trigger massive starbursts of star formation as the gas clouds in each galaxy are compressed and agitated by tidal forces. The latter mechanism may be responsible for the formation of globular clusters.

A supermassive black hole at the core of a galaxy may serve to regulate the rate of star formation in a galactic nucleus. A black hole that is accreting infalling matter can become active, emitting a strong wind through a collimated relativistic jet. This can limit further star formation. Massive black holes ejecting radio-frequency-emitting particles at near-light speed can also block the formation of new stars in aging galaxies. However, the radio emissions around the jets may also trigger star formation. Likewise, a weaker jet may trigger star formation when it collides with a cloud.

Dwarf galaxy ESO 553-46 has one of the highest rates of star formation of the 1000 or so galaxies nearest to the Milky Way.

As it collapses, a molecular cloud breaks into smaller and smaller pieces in a hierarchical manner, until the fragments reach stellar mass. In each of these fragments, the collapsing gas radiates away the energy gained by the release of gravitational potential energy. As the density increases, the fragments become opaque and are thus less efficient at radiating away their energy. This raises the temperature of the cloud and inhibits further fragmentation. The fragments now condense into rotating spheres of gas that serve as stellar embryos.

Complicating this picture of a collapsing cloud are the effects of turbulence, macroscopic flows, rotation, magnetic fields and the cloud geometry. Both rotation and magnetic fields can hinder the collapse of a cloud. Turbulence is instrumental in causing fragmentation of the cloud, and on the smallest scales it promotes collapse.

Main article: Protostar
LH 95 stellar nursery in Large Magellanic Cloud.

A protostellar cloud will continue to collapse as long as the gravitational binding energy can be eliminated. This excess energy is primarily lost through radiation. However, the collapsing cloud will eventually become opaque to its own radiation, and the energy must be removed through some other means. The dust within the cloud becomes heated to temperatures of60–100 K, and these particles radiate at wavelengths in the far infrared where the cloud is transparent. Thus the dust mediates the further collapse of the cloud.

During the collapse, the density of the cloud increases towards the center and thus the middle region becomes optically opaque first. This occurs when the density is about10−13 g / cm3. A core region, called the first hydrostatic core, forms where the collapse is essentially halted. It continues to increase in temperature as determined by the virial theorem. The gas falling toward this opaque region collides with it and creates shock waves that further heat the core.

Composite image showing young stars in and around molecular cloud Cepheus B.

When the core temperature reaches about2000 K, the thermal energy dissociates the H2 molecules. This is followed by the ionization of the hydrogen and helium atoms. These processes absorb the energy of the contraction, allowing it to continue on timescales comparable to the period of collapse at free fall velocities. After the density of infalling material has reached about 10−8 g / cm3, that material is sufficiently transparent to allow energy radiated by the protostar to escape. The combination of convection within the protostar and radiation from its exterior allow the star to contract further. This continues until the gas is hot enough for the internal pressure to support the protostar against further gravitational collapse—a state called hydrostatic equilibrium. When this accretion phase is nearly complete, the resulting object is known as a protostar.

N11, part of a complex network of gas clouds and star clusters within our neighbouring galaxy, the Large Magellanic Cloud.

Accretion of material onto the protostar continues partially from the newly formed circumstellar disc. When the density and temperature are high enough, deuterium fusion begins, and the outward pressure of the resultant radiation slows (but does not stop) the collapse. Material comprising the cloud continues to "rain" onto the protostar. In this stage bipolar jets are produced called Herbig–Haro objects. This is probably the means by which excess angular momentum of the infalling material is expelled, allowing the star to continue to form.

Star formation region Lupus 3.

When the surrounding gas and dust envelope disperses and accretion process stops, the star is considered a pre-main-sequence star (PMS star). The energy source of these objects is gravitational contraction, as opposed to hydrogen burning in main sequence stars. The PMS star follows a Hayashi track on the Hertzsprung–Russell (H–R) diagram. The contraction will proceed until the Hayashi limit is reached, and thereafter contraction will continue on a Kelvin–Helmholtz timescale with the temperature remaining stable. Stars with less than 0.5 M thereafter join the main sequence. For more massive PMS stars, at the end of the Hayashi track they will slowly collapse in near hydrostatic equilibrium, following the Henyey track.

Finally, hydrogen begins to fuse in the core of the star, and the rest of the enveloping material is cleared away. This ends the protostellar phase and begins the star's main sequence phase on the H–R diagram.

The stages of the process are well defined in stars with masses around 1 M or less. In high mass stars, the length of the star formation process is comparable to the other timescales of their evolution, much shorter, and the process is not so well defined. The later evolution of stars is studied in stellar evolution.

Protostar
Protostar outburst - HOPS 383 (2015).
The Orion Nebula is an archetypical example of star formation, from the massive, young stars that are shaping the nebula to the pillars of dense gas that may be the homes of budding stars.

Key elements of star formation are only available by observing in wavelengths other than the optical. The protostellar stage of stellar existence is almost invariably hidden away deep inside dense clouds of gas and dust left over from the GMC. Often, these star-forming cocoons known as Bok globules, can be seen in silhouette against bright emission from surrounding gas. Early stages of a star's life can be seen in infrared light, which penetrates the dust more easily than visible light. Observations from the Wide-field Infrared Survey Explorer (WISE) have thus been especially important for unveiling numerous galactic protostars and their parent star clusters. Examples of such embedded star clusters are FSR 1184, FSR 1190, Camargo 14, Camargo 74, Majaess 64, and Majaess 98.

Star-forming region S106.

The structure of the molecular cloud and the effects of the protostar can be observed in near-IR extinction maps (where the number of stars are counted per unit area and compared to a nearby zero extinction area of sky), continuum dust emission and rotational transitions of CO and other molecules; these last two are observed in the millimeter and submillimeter range. The radiation from the protostar and early star has to be observed in infrared astronomy wavelengths, as the extinction caused by the rest of the cloud in which the star is forming is usually too big to allow us to observe it in the visual part of the spectrum. This presents considerable difficulties as the Earth's atmosphere is almost entirely opaque from 20μm to 850μm, with narrow windows at 200μm and 450μm. Even outside this range, atmospheric subtraction techniques must be used.

Young stars (purple) revealed by X-ray inside the NGC 2024 star-forming region.

X-ray observations have proven useful for studying young stars, since X-ray emission from these objects is about 100–100,000 times stronger than X-ray emission from main-sequence stars. The earliest detections of X-rays from T Tauri stars were made by the Einstein X-ray Observatory. For low-mass stars X-rays are generated by the heating of the stellar corona through magnetic reconnection, while for high-mass O and early B-type stars X-rays are generated through supersonic shocks in the stellar winds. Photons in the soft X-ray energy range covered by the Chandra X-ray Observatory and XMM-Newton may penetrate the interstellar medium with only moderate absorption due to gas, making the X-ray a useful wavelength for seeing the stellar populations within molecular clouds. X-ray emission as evidence of stellar youth makes this band particularly useful for performing censuses of stars in star-forming regions, given that not all young stars have infrared excesses. X-ray observations have provided near-complete censuses of all stellar-mass objects in the Orion Nebula Cluster and Taurus Molecular Cloud.

The formation of individual stars can only be directly observed in the Milky Way Galaxy, but in distant galaxies star formation has been detected through its unique spectral signature.

Initial research indicates star-forming clumps start as giant, dense areas in turbulent gas-rich matter in young galaxies, live about 500 million years, and may migrate to the center of a galaxy, creating the central bulge of a galaxy.

On February 21, 2014, NASA announced a greatly upgraded database for tracking polycyclic aromatic hydrocarbons (PAHs) in the universe. According to scientists, more than 20% of the carbon in the universe may be associated with PAHs, possible starting materials for the formation of life. PAHs seem to have been formed shortly after the Big Bang, are widespread throughout the universe, and are associated with new stars and exoplanets.

In February 2018, astronomers reported, for the first time, a signal of the reionization epoch, an indirect detection of light from the earliest stars formed - about 180 million years after the Big Bang.

An article published on October 22, 2019, reported on the detection of 3MM-1, a massive star-forming galaxy about 12.5 billion light-years away that is obscured by clouds of dust. At a mass of about 1010.8 solar masses, it showed a star formation rate about 100 times as high as in the Milky Way.

Notable pathfinder objects

  • MWC 349 was first discovered in 1978, and is estimated to be only 1,000 years old.
  • VLA 1623 – The first exemplar Class 0 protostar, a type of embedded protostar that has yet to accrete the majority of its mass. Found in 1993, is possibly younger than 10,000 years.
  • L1014 – An extremely faint embedded object representative of a new class of sources that are only now being detected with the newest telescopes. Their status is still undetermined, they could be the youngest low-mass Class 0 protostars yet seen or even very low-mass evolved objects (like brown dwarfs or even rogue planets).
  • GCIRS 8* – The youngest known main sequence star in the Galactic Center region, discovered in August 2006. It is estimated to be 3.5 million years old.
Star-forming region Westerhout 40 and the Serpens-Aquila Rift- cloud filaments containing new stars fill the region.

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 8 M, 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. 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. 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. 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.

Another theory of massive star formation suggests that massive stars may form by the coalescence of two or more stars of lower mass.

  1. Stahler, S. W. & Palla, F. (2004). The Formation of Stars. Weinheim: Wiley-VCH. ISBN 3-527-40559-3.
  2. Lada, Charles J.; Lada, Elizabeth A. (2003-09-01). "Embedded Clusters in Molecular Clouds". Annual Review of Astronomy and Astrophysics. 41 (1): 57–115. arXiv:astro-ph/0301540. Bibcode:2003ARA&A..41...57L. doi:10.1146/annurev.astro.41.011802.094844. ISSN 0066-4146. S2CID 16752089.
  3. O'Dell, C. R. "Nebula". World Book at NASA. World Book, Inc. Archived from the original on 2005-04-29. Retrieved2009-05-18.
  4. Prialnik, Dina (2000). An Introduction to the Theory of Stellar Structure and Evolution. Cambridge University Press. 195–212. ISBN 0-521-65065-8.
  5. Dupraz, C.; Casoli, F. (June 4–9, 1990). "The Fate of the Molecular Gas from Mergers to Ellipticals". Dynamics of Galaxies and Their Molecular Cloud Distributions: Proceedings of the 146th Symposium of the International Astronomical Union. Paris, France: Kluwer Academic Publishers. Bibcode:1991IAUS..146..373D.
  6. Zhang, Guo-Yin; André, Ph; Men'shchikov, A.; Wang, Ke (October 2020). "Fragmentation of star-forming filaments in the X-shaped nebula of the California molecular cloud". Astronomy and Astrophysics. 642: A76. arXiv:2002.05984. Bibcode:2020A&A...642A..76Z. doi:10.1051/0004-6361/202037721. ISSN 0004-6361. S2CID 211126855.
  7. Lequeux, James (2013). Birth, Evolution and Death of Stars. World Scientific. ISBN 978-981-4508-77-3.
  8. Williams, J. P.; Blitz, L.; McKee, C. F. (2000). "The Structure and Evolution of Molecular Clouds: from Clumps to Cores to the IMF". Protostars and Planets IV. p. 97. arXiv:astro-ph/9902246. Bibcode:2000prpl.conf...97W.
  9. Alves, J.; Lada, C.; Lada, E. (2001). "Tracing H2 Via Infrared Dust Extinction". Molecular hydrogen in space. Cambridge University Press. p. 217. ISBN 0-521-78224-4.
  10. Sanders, D. B.; Scoville, N. Z.; Solomon, P. M. (1985-02-01). "Giant molecular clouds in the Galaxy. II – Characteristics of discrete features". Astrophysical Journal, Part 1. 289: 373–387. Bibcode:1985ApJ...289..373S. doi:10.1086/162897.
  11. Sandstrom, Karin M.; Peek, J. E. G.; Bower, Geoffrey C.; Bolatto, Alberto D.; Plambeck, Richard L. (2007). "A Parallactic Distance of 389 21 + 24 {\displaystyle 389_{-21}^{+24}} Parsecs to the Orion Nebula Cluster from Very Long Baseline Array Observations". The Astrophysical Journal. 667 (2): 1161. arXiv:0706.2361. Bibcode:2007ApJ...667.1161S. doi:10.1086/520922. S2CID 18192326.
  12. Wilking, B. A.; Gagné, M.; Allen, L. E. (2008). "Star Formation in the ρ Ophiuchi Molecular Cloud". In Bo Reipurth (ed.). Handbook of Star Forming Regions, Volume II: The Southern Sky ASP Monograph Publications. arXiv:0811.0005. Bibcode:2008hsf2.book..351W.
  13. Khanzadyan, T.; Smith, M. D.; Gredel, R.; Stanke, T.; Davis, C. J. (February 2002). "Active star formation in the large Bok globule CB 34". Astronomy and Astrophysics. 383 (2): 502–518. Bibcode:2002A&A...383..502K. doi:10.1051/0004-6361:20011531.
  14. Hartmann, Lee (2000). Accretion Processes in Star Formation. Cambridge University Press. p. 4. ISBN 0-521-78520-0.
  15. Smith, Michael David (2004). The Origin of Stars. Imperial College Press. pp. 43–44. ISBN 1-86094-501-5.
  16. "ALMA Witnesses Assembly of Galaxies in the Early Universe for the First Time". Retrieved23 July 2015.
  17. Kwok, Sun (2006).Physics and chemistry of the interstellar medium. University Science Books. pp. 435–437. ISBN 1-891389-46-7.
  18. Battaner, E. (1996). Astrophysical Fluid Dynamics. Cambridge University Press. pp. 166–167. ISBN 0-521-43747-4.
  19. "ALMA Captures Dramatic Stellar Fireworks". www.eso.org. Retrieved10 April 2017.
  20. Jog, C. J. (August 26–30, 1997). "Starbursts Triggered by Cloud Compression in Interacting Galaxies". In Barnes, J. E.; Sanders, D. B. (eds.). Proceedings of IAU Symposium #186, Galaxy Interactions at Low and High Redshift. Kyoto, Japan. Bibcode:1999IAUS..186..235J.
  21. Keto, Eric; Ho, Luis C.; Lo, K.-Y. (December 2005). "M82, Starbursts, Star Clusters, and the Formation of Globular Clusters". The Astrophysical Journal. 635 (2): 1062–1076. arXiv:astro-ph/0508519. Bibcode:2005ApJ...635.1062K. doi:10.1086/497575. S2CID 119359557.
  22. Gralla, Meg; et al. (September 29, 2014). "A measurement of the millimetre emission and the Sunyaev–Zel'dovich effect associated with low-frequency radio sources". Monthly Notices of the Royal Astronomical Society. Oxford University Press. 445 (1): 460–478. arXiv:1310.8281. Bibcode:2014MNRAS.445..460G. doi:10.1093/mnras/stu1592. S2CID 8171745.
  23. van Breugel, Wil; et al. (November 2004). T. Storchi-Bergmann; L.C. Ho; Henrique R. Schmitt (eds.). The Interplay among Black Holes, Stars and ISM in Galactic Nuclei. Cambridge University Press. pp. 485–488. arXiv:astro-ph/0406668. Bibcode:2004IAUS..222..485V. doi:10.1017/S1743921304002996.
  24. "Size can be deceptive". www.spacetelescope.org. Retrieved9 October 2017.
  25. Prialnik, Dina (2000). An Introduction to the Theory of Stellar Structure and Evolution. Cambridge University Press. pp. 198–199. ISBN 0-521-65937-X.
  26. Hartmann, Lee (2000). Accretion Processes in Star Formation. Cambridge University Press. p. 22. ISBN 0-521-78520-0.
  27. Li, Hua-bai; Dowell, C. Darren; Goodman, Alyssa; Hildebrand, Roger; Novak, Giles (2009-08-11). "Anchoring Magnetic Field in Turbulent Molecular Clouds". The Astrophysical Journal. 704 (2): 891. arXiv:0908.1549. Bibcode:2009ApJ...704..891L. doi:10.1088/0004-637X/704/2/891. S2CID 118341372.
  28. Ballesteros-Paredes, J.; Klessen, R. S.; Mac Low, M.-M.; Vazquez-Semadeni, E. (2007). "Molecular Cloud Turbulence and Star Formation". In Reipurth, B.; Jewitt, D.; Keil, K. (eds.). Protostars and Planets V. pp. 63–80. ISBN 978-0-8165-2654-3.
  29. Longair, M. S. (2008). Galaxy Formation (2nd ed.). Springer. p. 478. ISBN 978-3-540-73477-2.
  30. Larson, Richard B. (1969). "Numerical calculations of the dynamics of collapsing proto-star". Monthly Notices of the Royal Astronomical Society. 145 (3): 271–295. Bibcode:1969MNRAS.145..271L. doi:10.1093/mnras/145.3.271.
  31. Salaris, Maurizio (2005). Cassisi, Santi (ed.).Evolution of stars and stellar populations. John Wiley and Sons. pp. 108–109. ISBN 0-470-09220-3.
  32. "Glory From Gloom". www.eso.org. Retrieved2 February 2018.
  33. C. Hayashi (1961). "Stellar evolution in early phases of gravitational contraction". Publications of the Astronomical Society of Japan. 13: 450–452. Bibcode:1961PASJ...13..450H.
  34. L. G. Henyey; R. Lelevier; R. D. Levée (1955). "The Early Phases of Stellar Evolution". Publications of the Astronomical Society of the Pacific. 67 (396): 154. Bibcode:1955PASP...67..154H. doi:10.1086/126791.
  35. B. J. Bok & E. F. Reilly (1947). "Small Dark Nebulae". Astrophysical Journal. 105: 255. Bibcode:1947ApJ...105..255B. doi:10.1086/144901.
    Yun, Joao Lin; Clemens, Dan P. (1990). "Star formation in small globules – Bart BOK was correct". The Astrophysical Journal. 365: L73. Bibcode:1990ApJ...365L..73Y. doi:10.1086/185891.
  36. Benjamin, Robert A.; Churchwell, E.; Babler, Brian L.; Bania, T. M.; Clemens, Dan P.; Cohen, Martin; Dickey, John M.; Indebetouw, Rémy; et al. (2003). "GLIMPSE. I. An SIRTF Legacy Project to Map the Inner Galaxy". Publications of the Astronomical Society of the Pacific. 115 (810): 953–964. arXiv:astro-ph/0306274. Bibcode:2003PASP..115..953B. doi:10.1086/376696. S2CID 119510724.
  37. "Wide-field Infrared Survey Explorer Mission". NASA.
  38. Majaess, D. (2013). Discovering protostars and their host clusters via WISE, ApSS, 344, 1 (VizieR catalog)
  39. Camargo et al. (2015). New Galactic embedded clusters and candidates from a WISE Survey, New Astronomy, 34
  40. Getman, K.; et al. (2014). "Core-Halo Age Gradients and Star Formation in the Orion Nebula and NGC 2024 Young Stellar Clusters". Astrophysical Journal Supplement. 787 (2): 109. arXiv:1403.2742. Bibcode:2014ApJ...787..109G. doi:10.1088/0004-637X/787/2/109. S2CID 118503957.
  41. Preibisch, T.; et al. (2005). "The Origin of T Tauri X-Ray Emission: New Insights from the Chandra Orion Ultradeep Project". Astrophysical Journal Supplement. 160 (2): 401–422. arXiv:astro-ph/0506526. Bibcode:2005ApJS..160..401P. doi:10.1086/432891. S2CID 18155082.
  42. Feigelson, E. D.; Decampli, W. M. (1981). "Observations of X-ray emission from T-Tauri stars". Astrophysical Journal Letters. 243: L89–L93. Bibcode:1981ApJ...243L..89F. doi:10.1086/183449.
  43. Montmerle, T.; et al. (1983). "Einstein observations of the Rho Ophiuchi dark cloud - an X-ray Christmas tree". Astrophysical Journal, Part 1. 269: 182–201. Bibcode:1983ApJ...269..182M. doi:10.1086/161029.
  44. Feigelson, E. D.; et al. (2013). "Overview of the Massive Young Star-Forming Complex Study in Infrared and X-Ray (MYStIX) Project". Astrophysical Journal Supplement. 209 (2): 26. arXiv:1309.4483. Bibcode:2013ApJS..209...26F. doi:10.1088/0067-0049/209/2/26. S2CID 56189137.
  45. Getman, K. V.; et al. (2005). "Chandra Orion Ultradeep Project: Observations and Source Lists". Astrophysical Journal Supplement. 160 (2): 319–352. arXiv:astro-ph/0410136. Bibcode:2005ApJS..160..319G. doi:10.1086/432092. S2CID 19965900.
  46. Güdel, M.; et al. (2007). "The XMM-Newton extended survey of the Taurus molecular cloud (XEST)". Astronomy and Astrophysics. 468 (2): 353–377. arXiv:astro-ph/0609160. Bibcode:2007A&A...468..353G. doi:10.1051/0004-6361:20065724. S2CID 8846597.
  47. "Young Star-Forming Clump in Deep Space Spotted for First Time". 10 May 2015. Retrieved2015-05-11.
  48. Hoover, Rachel (February 21, 2014). "Need to Track Organic Nano-Particles Across the Universe? NASA's Got an App for That". NASA. RetrievedFebruary 22, 2014.
  49. Gibney, Elizabeth (February 28, 2018). "Astronomers detect light from the Universe's first stars - Surprises in signal from cosmic dawn also hint at presence of dark matter". Nature. doi:10.1038/d41586-018-02616-8. RetrievedFebruary 28, 2018.
  50. Williams, Christina C.; Labbe, Ivo; Spilker, Justin; Stefanon, Mauro; Leja, Joel; Whitaker, Katherine; Bezanson, Rachel; Narayanan, Desika; Oesch, Pascal; Weiner, Benjamin (2019). "Discovery of a Dark, Massive, ALMA-only Galaxy at z ∼ 5–6 in a Tiny 3 mm Survey". The Astrophysical Journal. 884 (2): 154. arXiv:1905.11996. Bibcode:2019ApJ...884..154W. doi:10.3847/1538-4357/ab44aa. ISSN 1538-4357. S2CID 168169681.
  51. University of Arizona (22 October 2019). "Cosmic Yeti from the Dawn of the Universe Found Lurking in Dust". UANews. Retrieved2019-10-22.
  52. Andre, Philippe; Ward-Thompson, Derek; Barsony, Mary (1993). "Submillimeter continuum observations of Rho Ophiuchi A - The candidate protostar VLA 1623 and prestellar clumps". The Astrophysical Journal. 406: 122–141. Bibcode:1993ApJ...406..122A. doi:10.1086/172425. ISSN 0004-637X.
  53. Bourke, Tyler L.; Crapsi, Antonio; Myers, Philip C.; et al. (2005). "Discovery of a Low-Mass Bipolar Molecular Outflow from L1014-IRS with the Submillimeter Array". The Astrophysical Journal. 633 (2): L129. arXiv:astro-ph/0509865. Bibcode:2005ApJ...633L.129B. doi:10.1086/498449. S2CID 14721548.
  54. Geballe, T. R.; Najarro, F.; Rigaut, F.; Roy, J.‐R. (2006). "TheK‐Band Spectrum of the Hot Star in IRS 8: An Outsider in the Galactic Center?". The Astrophysical Journal. 652 (1): 370–375. arXiv:astro-ph/0607550. Bibcode:2006ApJ...652..370G. doi:10.1086/507764. ISSN 0004-637X. S2CID 9998286.
  55. Kuhn, M. A.; et al. (2010). "A Chandra Observation of the Obscured Star-forming Complex W40". Astrophysical Journal. 725 (2): 2485–2506. arXiv:1010.5434. Bibcode:2010ApJ...725.2485K. doi:10.1088/0004-637X/725/2/2485. S2CID 119192761.
  56. André, Ph.; et al. (2010). "From filamentary clouds to prestellar cores to the stellar IMF: Initial highlights from the Herschel Gould Belt Survey". Astronomy & Astrophysics. 518: L102. arXiv:1005.2618. Bibcode:2010A&A...518L.102A. doi:10.1051/0004-6361/201014666. S2CID 248768.
  57. M. G. Wolfire; J. P. Cassinelli (1987). "Conditions for the formation of massive stars". Astrophysical Journal. 319 (1): 850–867. Bibcode:1987ApJ...319..850W. doi:10.1086/165503.
  58. C. F. McKee; J. C. Tan (2002). "Massive star formation in 100,000 years from turbulent and pressurized molecular clouds". Nature. 416 (6876): 59–61. arXiv:astro-ph/0203071. Bibcode:2002Natur.416...59M. doi:10.1038/416059a. PMID 11882889. S2CID 4330710.
  59. R. Banerjee; R. E. Pudritz (2007). "Massive star formation via high accretion rates and early disk-driven outflows". Astrophysical Journal. 660 (1): 479–488. arXiv:astro-ph/0612674. Bibcode:2007ApJ...660..479B. doi:10.1086/512010. S2CID 9769562.
  60. I. A. Bonnell; M. R. Bate; C. J. Clarke; J. E. Pringle (1997). "Accretion and the stellar mass spectrum in small clusters". Monthly Notices of the Royal Astronomical Society. 285 (1): 201–208. Bibcode:1997MNRAS.285..201B. doi:10.1093/mnras/285.1.201.
  61. I. A. Bonnell; M. R. Bate (2006). "Star formation through gravitational collapse and competitive accretion". Monthly Notices of the Royal Astronomical Society. 370 (1): 488–494. arXiv:astro-ph/0604615. Bibcode:2006MNRAS.370..488B. doi:10.1111/j.1365-2966.2006.10495.x. S2CID 15652967.
  62. I. A. Bonnell; M. R. Bate; H. Zinnecker (1998). "On the formation of massive stars". Monthly Notices of the Royal Astronomical Society. 298 (1): 93–102. arXiv:astro-ph/9802332. Bibcode:1998MNRAS.298...93B. doi:10.1046/j.1365-8711.1998.01590.x. S2CID 119346630.

Star formation
Star formation Language Watch Edit Star formation is the process by which dense regions within molecular clouds in interstellar space sometimes referred to as stellar nurseries or star forming regions collapse and form stars 1 As a branch of astronomy star formation includes the study of the interstellar medium ISM and giant molecular clouds GMC as precursors to the star formation process and the study of protostars and young stellar objects as its immediate products It is closely related to planet formation another branch of astronomy Star formation theory as well as accounting for the formation of a single star must also account for the statistics of binary stars and the initial mass function Most stars do not form in isolation but as part of a group of stars referred as star clusters or stellar associations 2 Contents 1 Stellar nurseries 1 1 Interstellar clouds 1 2 Cloud collapse 2 Protostar 3 Observations 3 1 Notable pathfinder objects 4 Low mass and high mass star formation 5 See also 6 ReferencesStellar nurseries Edit Hubble telescope image known as Pillars of Creation where stars are forming in the Eagle Nebula Interstellar clouds Edit The W51 nebula in Aquila one of the largest star factories in the Milky Way August 25 2020 A spiral galaxy like the Milky Way contains stars stellar remnants and a diffuse interstellar medium ISM of gas and dust The interstellar medium consists of 10 4 to 106 particles per cm3 and is typically composed of roughly 70 hydrogen by mass with most of the remaining gas consisting of helium This medium has been chemically enriched by trace amounts of heavier elements that were produced and ejected from stars via the fusion of helium as they passed beyond the end of their main sequence lifetime Higher density regions of the interstellar medium form clouds or diffuse nebulae 3 where star formation takes place 4 In contrast to spirals an elliptical galaxy loses the cold component of its interstellar medium within roughly a billion years which hinders the galaxy from forming diffuse nebulae except through mergers with other galaxies 5 In the dense nebulae where stars are produced much of the hydrogen is in the molecular H2 form so these nebulae are called molecular clouds 4 Herschel Space Observatory have revealed that filaments are truly ubiquitous in the molecular cloud Dense molecular filaments which are central to the star formation process will fragment into gravitationally bound cores most of which will evolve into stars Continuous accretion of gas geometrical bending and magnetic fields may control the detailed fragmentation manner of the filaments In supercritical filaments observations have revealed quasi periodic chains of dense cores with spacing comparable to the filament inner width and includes embedded protostars with outflows 6 Observations indicate that the coldest clouds tend to form low mass stars observed first in the infrared inside the clouds then in visible light at their surface when the clouds dissipate while giant molecular clouds which are generally warmer produce stars of all masses 7 These giant molecular clouds have typical densities of 100 particles per cm3 diameters of 100 light years 9 5 1014 km masses of up to 6 million solar masses M 8 and an average interior temperature of 10 K About half the total mass of the galactic ISM is found in molecular clouds 9 and in the Milky Way there are an estimated 6 000 molecular clouds each with more than 100 000 M 10 The nearest nebula to the Sun where massive stars are being formed is the Orion Nebula 1 300 ly 1 2 1016 km away 11 However lower mass star formation is occurring about 400 450 light years distant in the r Ophiuchi cloud complex 12 A more compact site of star formation is the opaque clouds of dense gas and dust known as Bok globules so named after the astronomer Bart Bok These can form in association with collapsing molecular clouds or possibly independently 13 The Bok globules are typically up to a light year across and contain a few solar masses 14 They can be observed as dark clouds silhouetted against bright emission nebulae or background stars Over half the known Bok globules have been found to contain newly forming stars 15 Assembly of galaxy in early Universe 16 Cloud collapse Edit An interstellar cloud of gas will remain in hydrostatic equilibrium as long as the kinetic energy of the gas pressure is in balance with the potential energy of the internal gravitational force Mathematically this is expressed using the virial theorem which states that to maintain equilibrium the gravitational potential energy must equal twice the internal thermal energy 17 If a cloud is massive enough that the gas pressure is insufficient to support it the cloud will undergo gravitational collapse The mass above which a cloud will undergo such collapse is called the Jeans mass The Jeans mass depends on the temperature and density of the cloud but is typically thousands to tens of thousands of solar masses 4 During cloud collapse dozens to tens of thousands of stars form more or less simultaneously which is observable in so called embedded clusters The end product of a core collapse is an open cluster of stars 18 ALMA observations of the Orion Nebula complex provide insights into explosions at star birth 19 In triggered star formation one of several events might occur to compress a molecular cloud and initiate its gravitational collapse Molecular clouds may collide with each other or a nearby supernova explosion can be a trigger sending shocked matter into the cloud at very high speeds 4 The resulting new stars may themselves soon produce supernovae producing self propagating star formation Alternatively galactic collisions can trigger massive starbursts of star formation as the gas clouds in each galaxy are compressed and agitated by tidal forces 20 The latter mechanism may be responsible for the formation of globular clusters 21 A supermassive black hole at the core of a galaxy may serve to regulate the rate of star formation in a galactic nucleus A black hole that is accreting infalling matter can become active emitting a strong wind through a collimated relativistic jet This can limit further star formation Massive black holes ejecting radio frequency emitting particles at near light speed can also block the formation of new stars in aging galaxies 22 However the radio emissions around the jets may also trigger star formation Likewise a weaker jet may trigger star formation when it collides with a cloud 23 Dwarf galaxy ESO 553 46 has one of the highest rates of star formation of the 1000 or so galaxies nearest to the Milky Way 24 As it collapses a molecular cloud breaks into smaller and smaller pieces in a hierarchical manner until the fragments reach stellar mass In each of these fragments the collapsing gas radiates away the energy gained by the release of gravitational potential energy As the density increases the fragments become opaque and are thus less efficient at radiating away their energy This raises the temperature of the cloud and inhibits further fragmentation The fragments now condense into rotating spheres of gas that serve as stellar embryos 25 Complicating this picture of a collapsing cloud are the effects of turbulence macroscopic flows rotation magnetic fields and the cloud geometry Both rotation and magnetic fields can hinder the collapse of a cloud 26 27 Turbulence is instrumental in causing fragmentation of the cloud and on the smallest scales it promotes collapse 28 Protostar EditMain article Protostar LH 95 stellar nursery in Large Magellanic Cloud A protostellar cloud will continue to collapse as long as the gravitational binding energy can be eliminated This excess energy is primarily lost through radiation However the collapsing cloud will eventually become opaque to its own radiation and the energy must be removed through some other means The dust within the cloud becomes heated to temperatures of 60 100 K and these particles radiate at wavelengths in the far infrared where the cloud is transparent Thus the dust mediates the further collapse of the cloud 29 During the collapse the density of the cloud increases towards the center and thus the middle region becomes optically opaque first This occurs when the density is about 10 13 g cm3 A core region called the first hydrostatic core forms where the collapse is essentially halted It continues to increase in temperature as determined by the virial theorem The gas falling toward this opaque region collides with it and creates shock waves that further heat the core 30 Composite image showing young stars in and around molecular cloud Cepheus B When the core temperature reaches about 2000 K the thermal energy dissociates the H2 molecules 30 This is followed by the ionization of the hydrogen and helium atoms These processes absorb the energy of the contraction allowing it to continue on timescales comparable to the period of collapse at free fall velocities 31 After the density of infalling material has reached about 10 8 g cm3 that material is sufficiently transparent to allow energy radiated by the protostar to escape The combination of convection within the protostar and radiation from its exterior allow the star to contract further 30 This continues until the gas is hot enough for the internal pressure to support the protostar against further gravitational collapse a state called hydrostatic equilibrium When this accretion phase is nearly complete the resulting object is known as a protostar 4 N11 part of a complex network of gas clouds and star clusters within our neighbouring galaxy the Large Magellanic Cloud Accretion of material onto the protostar continues partially from the newly formed circumstellar disc When the density and temperature are high enough deuterium fusion begins and the outward pressure of the resultant radiation slows but does not stop the collapse Material comprising the cloud continues to rain onto the protostar In this stage bipolar jets are produced called Herbig Haro objects This is probably the means by which excess angular momentum of the infalling material is expelled allowing the star to continue to form Star formation region Lupus 3 32 When the surrounding gas and dust envelope disperses and accretion process stops the star is considered a pre main sequence star PMS star The energy source of these objects is gravitational contraction as opposed to hydrogen burning in main sequence stars The PMS star follows a Hayashi track on the Hertzsprung Russell H R diagram 33 The contraction will proceed until the Hayashi limit is reached and thereafter contraction will continue on a Kelvin Helmholtz timescale with the temperature remaining stable Stars with less than 0 5 M thereafter join the main sequence For more massive PMS stars at the end of the Hayashi track they will slowly collapse in near hydrostatic equilibrium following the Henyey track 34 Finally hydrogen begins to fuse in the core of the star and the rest of the enveloping material is cleared away This ends the protostellar phase and begins the star s main sequence phase on the H R diagram The stages of the process are well defined in stars with masses around 1 M or less In high mass stars the length of the star formation process is comparable to the other timescales of their evolution much shorter and the process is not so well defined The later evolution of stars is studied in stellar evolution Protostar Protostar outburst HOPS 383 2015 Observations Edit The Orion Nebula is an archetypical example of star formation from the massive young stars that are shaping the nebula to the pillars of dense gas that may be the homes of budding stars Key elements of star formation are only available by observing in wavelengths other than the optical The protostellar stage of stellar existence is almost invariably hidden away deep inside dense clouds of gas and dust left over from the GMC Often these star forming cocoons known as Bok globules can be seen in silhouette against bright emission from surrounding gas 35 Early stages of a star s life can be seen in infrared light which penetrates the dust more easily than visible light 36 Observations from the Wide field Infrared Survey Explorer WISE have thus been especially important for unveiling numerous galactic protostars and their parent star clusters 37 38 Examples of such embedded star clusters are FSR 1184 FSR 1190 Camargo 14 Camargo 74 Majaess 64 and Majaess 98 39 Star forming region S106 The structure of the molecular cloud and the effects of the protostar can be observed in near IR extinction maps where the number of stars are counted per unit area and compared to a nearby zero extinction area of sky continuum dust emission and rotational transitions of CO and other molecules these last two are observed in the millimeter and submillimeter range The radiation from the protostar and early star has to be observed in infrared astronomy wavelengths as the extinction caused by the rest of the cloud in which the star is forming is usually too big to allow us to observe it in the visual part of the spectrum This presents considerable difficulties as the Earth s atmosphere is almost entirely opaque from 20mm to 850mm with narrow windows at 200mm and 450mm Even outside this range atmospheric subtraction techniques must be used Young stars purple revealed by X ray inside the NGC 2024 star forming region 40 X ray observations have proven useful for studying young stars since X ray emission from these objects is about 100 100 000 times stronger than X ray emission from main sequence stars 41 The earliest detections of X rays from T Tauri stars were made by the Einstein X ray Observatory 42 43 For low mass stars X rays are generated by the heating of the stellar corona through magnetic reconnection while for high mass O and early B type stars X rays are generated through supersonic shocks in the stellar winds Photons in the soft X ray energy range covered by the Chandra X ray Observatory and XMM Newton may penetrate the interstellar medium with only moderate absorption due to gas making the X ray a useful wavelength for seeing the stellar populations within molecular clouds X ray emission as evidence of stellar youth makes this band particularly useful for performing censuses of stars in star forming regions given that not all young stars have infrared excesses 44 X ray observations have provided near complete censuses of all stellar mass objects in the Orion Nebula Cluster and Taurus Molecular Cloud 45 46 The formation of individual stars can only be directly observed in the Milky Way Galaxy but in distant galaxies star formation has been detected through its unique spectral signature Initial research indicates star forming clumps start as giant dense areas in turbulent gas rich matter in young galaxies live about 500 million years and may migrate to the center of a galaxy creating the central bulge of a galaxy 47 On February 21 2014 NASA announced a greatly upgraded database for tracking polycyclic aromatic hydrocarbons PAHs in the universe According to scientists more than 20 of the carbon in the universe may be associated with PAHs possible starting materials for the formation of life PAHs seem to have been formed shortly after the Big Bang are widespread throughout the universe and are associated with new stars and exoplanets 48 In February 2018 astronomers reported for the first time a signal of the reionization epoch an indirect detection of light from the earliest stars formed about 180 million years after the Big Bang 49 An article published on October 22 2019 reported on the detection of 3MM 1 a massive star forming galaxy about 12 5 billion light years away that is obscured by clouds of dust 50 At a mass of about 1010 8 solar masses it showed a star formation rate about 100 times as high as in the Milky Way 51 Notable pathfinder objects Edit MWC 349 was first discovered in 1978 and is estimated to be only 1 000 years old VLA 1623 The first exemplar Class 0 protostar a type of embedded protostar that has yet to accrete the majority of its mass Found in 1993 is possibly younger than 10 000 years 52 L1014 An extremely faint embedded object representative of a new class of sources that are only now being detected with the newest telescopes Their status is still undetermined they could be the youngest low mass Class 0 protostars yet seen or even very low mass evolved objects like brown dwarfs or even rogue planets 53 GCIRS 8 The youngest known main sequence star in the Galactic Center region discovered in August 2006 It is estimated to be 3 5 million years old 54 Low mass and high mass star formation Edit Star forming region Westerhout 40 and the Serpens Aquila Rift cloud filaments containing new stars fill the region 55 56 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 8 M 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 57 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 58 59 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 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 60 61 Another theory of massive star formation suggests that massive stars may form by the coalescence of two or more stars of lower mass 62 See also EditAccretion Accumulation of particles into a massive object by gravitationally attracting more matter Champagne flow model Chronology of the universe History and future of the universe Formation and evolution of the Solar System Formation of the Solar System by gravitational collapse of a molecular cloud and subsequent geological history Galaxy formation and evolution from a homogeneous beginning the formation of the first galaxies the way galaxies change over time List of star forming regions in the Local Group Regions in the Milky Way galaxy and Local Group where new stars are formingReferences Edit Stahler S W amp Palla F 2004 The Formation of Stars Weinheim Wiley VCH ISBN 3 527 40559 3 Lada Charles J Lada Elizabeth A 2003 09 01 Embedded Clusters in Molecular Clouds Annual Review of Astronomy and Astrophysics 41 1 57 115 arXiv astro ph 0301540 Bibcode 2003ARA amp A 41 57L doi 10 1146 annurev astro 41 011802 094844 ISSN 0066 4146 S2CID 16752089 O Dell C R Nebula World Book at NASA World Book Inc Archived from the original on 2005 04 29 Retrieved 2009 05 18 a b c d e Prialnik Dina 2000 An Introduction to the Theory of Stellar Structure and Evolution Cambridge University Press 195 212 ISBN 0 521 65065 8 Dupraz C Casoli F June 4 9 1990 The Fate of the Molecular Gas from Mergers to Ellipticals Dynamics of Galaxies and Their Molecular Cloud Distributions Proceedings of the 146th Symposium of the International Astronomical Union Paris France Kluwer Academic Publishers Bibcode 1991IAUS 146 373D Zhang Guo Yin Andre Ph Men shchikov A Wang Ke October 2020 Fragmentation of star forming filaments in the X shaped nebula of the California molecular cloud Astronomy and Astrophysics 642 A76 arXiv 2002 05984 Bibcode 2020A amp A 642A 76Z doi 10 1051 0004 6361 202037721 ISSN 0004 6361 S2CID 211126855 Lequeux James 2013 Birth Evolution and Death of Stars World Scientific ISBN 978 981 4508 77 3 Williams J P Blitz L McKee C F 2000 The Structure and Evolution of Molecular Clouds from Clumps to Cores to the IMF Protostars and Planets IV p 97 arXiv astro ph 9902246 Bibcode 2000prpl conf 97W Alves J Lada C Lada E 2001 Tracing H2 Via Infrared Dust Extinction Molecular hydrogen in space Cambridge University Press p 217 ISBN 0 521 78224 4 Sanders D B Scoville N Z Solomon P M 1985 02 01 Giant molecular clouds in the Galaxy II Characteristics of discrete features Astrophysical Journal Part 1 289 373 387 Bibcode 1985ApJ 289 373S doi 10 1086 162897 Sandstrom Karin M Peek J E G Bower Geoffrey C Bolatto Alberto D Plambeck Richard L 2007 A Parallactic Distance of 389 21 24 displaystyle 389 21 24 Parsecs to the Orion Nebula Cluster from Very Long Baseline Array Observations The Astrophysical Journal 667 2 1161 arXiv 0706 2361 Bibcode 2007ApJ 667 1161S doi 10 1086 520922 S2CID 18192326 Wilking B A Gagne M Allen L E 2008 Star Formation in the r Ophiuchi Molecular Cloud In Bo Reipurth ed Handbook of Star Forming Regions Volume II The Southern Sky ASP Monograph Publications arXiv 0811 0005 Bibcode 2008hsf2 book 351W Khanzadyan T Smith M D Gredel R Stanke T Davis C J February 2002 Active star formation in the large Bok globule CB 34 Astronomy and Astrophysics 383 2 502 518 Bibcode 2002A amp A 383 502K doi 10 1051 0004 6361 20011531 Hartmann Lee 2000 Accretion Processes in Star Formation Cambridge University Press p 4 ISBN 0 521 78520 0 Smith Michael David 2004 The Origin of Stars Imperial College Press pp 43 44 ISBN 1 86094 501 5 ALMA Witnesses Assembly of Galaxies in the Early Universe for the First Time Retrieved 23 July 2015 Kwok Sun 2006 Physics and chemistry of the interstellar medium University Science Books pp 435 437 ISBN 1 891389 46 7 Battaner E 1996 Astrophysical Fluid Dynamics Cambridge University Press pp 166 167 ISBN 0 521 43747 4 ALMA Captures Dramatic Stellar Fireworks www eso org Retrieved 10 April 2017 Jog C J August 26 30 1997 Starbursts Triggered by Cloud Compression in Interacting Galaxies In Barnes J E Sanders D B eds Proceedings of IAU Symposium 186 Galaxy Interactions at Low and High Redshift Kyoto Japan Bibcode 1999IAUS 186 235J Keto Eric Ho Luis C Lo K Y December 2005 M82 Starbursts Star Clusters and the Formation of Globular Clusters The Astrophysical Journal 635 2 1062 1076 arXiv astro ph 0508519 Bibcode 2005ApJ 635 1062K doi 10 1086 497575 S2CID 119359557 Gralla Meg et al September 29 2014 A measurement of the millimetre emission and the Sunyaev Zel dovich effect associated with low frequency radio sources Monthly Notices of the Royal Astronomical Society Oxford University Press 445 1 460 478 arXiv 1310 8281 Bibcode 2014MNRAS 445 460G doi 10 1093 mnras stu1592 S2CID 8171745 van Breugel Wil et al November 2004 T Storchi Bergmann L C Ho Henrique R Schmitt eds The Interplay among Black Holes Stars and ISM in Galactic Nuclei Cambridge University Press pp 485 488 arXiv astro ph 0406668 Bibcode 2004IAUS 222 485V doi 10 1017 S1743921304002996 Size can be deceptive www spacetelescope org Retrieved 9 October 2017 Prialnik Dina 2000 An Introduction to the Theory of Stellar Structure and Evolution Cambridge University Press pp 198 199 ISBN 0 521 65937 X Hartmann Lee 2000 Accretion Processes in Star Formation Cambridge University Press p 22 ISBN 0 521 78520 0 Li Hua bai Dowell C Darren Goodman Alyssa Hildebrand Roger Novak Giles 2009 08 11 Anchoring Magnetic Field in Turbulent Molecular Clouds The Astrophysical Journal 704 2 891 arXiv 0908 1549 Bibcode 2009ApJ 704 891L doi 10 1088 0004 637X 704 2 891 S2CID 118341372 Ballesteros Paredes J Klessen R S Mac Low M M Vazquez Semadeni E 2007 Molecular Cloud Turbulence and Star Formation In Reipurth B Jewitt D Keil K eds Protostars and Planets V pp 63 80 ISBN 978 0 8165 2654 3 Longair M S 2008 Galaxy Formation 2nd ed Springer p 478 ISBN 978 3 540 73477 2 a b c Larson Richard B 1969 Numerical calculations of the dynamics of collapsing proto star Monthly Notices of the Royal Astronomical Society 145 3 271 295 Bibcode 1969MNRAS 145 271L doi 10 1093 mnras 145 3 271 Salaris Maurizio 2005 Cassisi Santi ed Evolution of stars and stellar populations John Wiley and Sons pp 108 109 ISBN 0 470 09220 3 Glory From Gloom www eso org Retrieved 2 February 2018 C Hayashi 1961 Stellar evolution in early phases of gravitational contraction Publications of the Astronomical Society of Japan 13 450 452 Bibcode 1961PASJ 13 450H L G Henyey R Lelevier R D Levee 1955 The Early Phases of Stellar Evolution Publications of the Astronomical Society of the Pacific 67 396 154 Bibcode 1955PASP 67 154H doi 10 1086 126791 B J Bok amp E F Reilly 1947 Small Dark Nebulae Astrophysical Journal 105 255 Bibcode 1947ApJ 105 255B doi 10 1086 144901 Yun Joao Lin Clemens Dan P 1990 Star formation in small globules Bart BOK was correct The Astrophysical Journal 365 L73 Bibcode 1990ApJ 365L 73Y doi 10 1086 185891 Benjamin Robert A Churchwell E Babler Brian L Bania T M Clemens Dan P Cohen Martin Dickey John M Indebetouw Remy et al 2003 GLIMPSE I An SIRTF Legacy Project to Map the Inner Galaxy Publications of the Astronomical Society of the Pacific 115 810 953 964 arXiv astro ph 0306274 Bibcode 2003PASP 115 953B doi 10 1086 376696 S2CID 119510724 Wide field Infrared Survey Explorer Mission NASA Majaess D 2013 Discovering protostars and their host clusters via WISE ApSS 344 1 VizieR catalog Camargo et al 2015 New Galactic embedded clusters and candidates from a WISE Survey New Astronomy 34 Getman K et al 2014 Core Halo Age Gradients and Star Formation in the Orion Nebula and NGC 2024 Young Stellar Clusters Astrophysical Journal Supplement 787 2 109 arXiv 1403 2742 Bibcode 2014ApJ 787 109G doi 10 1088 0004 637X 787 2 109 S2CID 118503957 Preibisch T et al 2005 The Origin of T Tauri X Ray Emission New Insights from the Chandra Orion Ultradeep Project Astrophysical Journal Supplement 160 2 401 422 arXiv astro ph 0506526 Bibcode 2005ApJS 160 401P doi 10 1086 432891 S2CID 18155082 Feigelson E D Decampli W M 1981 Observations of X ray emission from T Tauri stars Astrophysical Journal Letters 243 L89 L93 Bibcode 1981ApJ 243L 89F doi 10 1086 183449 Montmerle T et al 1983 Einstein observations of the Rho Ophiuchi dark cloud an X ray Christmas tree Astrophysical Journal Part 1 269 182 201 Bibcode 1983ApJ 269 182M doi 10 1086 161029 Feigelson E D et al 2013 Overview of the Massive Young Star Forming Complex Study in Infrared and X Ray MYStIX Project Astrophysical Journal Supplement 209 2 26 arXiv 1309 4483 Bibcode 2013ApJS 209 26F doi 10 1088 0067 0049 209 2 26 S2CID 56189137 Getman K V et al 2005 Chandra Orion Ultradeep Project Observations and Source Lists Astrophysical Journal Supplement 160 2 319 352 arXiv astro ph 0410136 Bibcode 2005ApJS 160 319G doi 10 1086 432092 S2CID 19965900 Gudel M et al 2007 The XMM Newton extended survey of the Taurus molecular cloud XEST Astronomy and Astrophysics 468 2 353 377 arXiv astro ph 0609160 Bibcode 2007A amp A 468 353G doi 10 1051 0004 6361 20065724 S2CID 8846597 Young Star Forming Clump in Deep Space Spotted for First Time 10 May 2015 Retrieved 2015 05 11 Hoover Rachel February 21 2014 Need to Track Organic Nano Particles Across the Universe NASA s Got an App for That NASA Retrieved February 22 2014 Gibney Elizabeth February 28 2018 Astronomers detect light from the Universe s first stars Surprises in signal from cosmic dawn also hint at presence of dark matter Nature doi 10 1038 d41586 018 02616 8 Retrieved February 28 2018 Williams Christina C Labbe Ivo Spilker Justin Stefanon Mauro Leja Joel Whitaker Katherine Bezanson Rachel Narayanan Desika Oesch Pascal Weiner Benjamin 2019 Discovery of a Dark Massive ALMA only Galaxy at z 5 6 in a Tiny 3 mm Survey The Astrophysical Journal 884 2 154 arXiv 1905 11996 Bibcode 2019ApJ 884 154W doi 10 3847 1538 4357 ab44aa ISSN 1538 4357 S2CID 168169681 University of Arizona 22 October 2019 Cosmic Yeti from the Dawn of the Universe Found Lurking in Dust UANews Retrieved 2019 10 22 Andre Philippe Ward Thompson Derek Barsony Mary 1993 Submillimeter continuum observations of Rho Ophiuchi A The candidate protostar VLA 1623 and prestellar clumps The Astrophysical Journal 406 122 141 Bibcode 1993ApJ 406 122A doi 10 1086 172425 ISSN 0004 637X Bourke Tyler L Crapsi Antonio Myers Philip C et al 2005 Discovery of a Low Mass Bipolar Molecular Outflow from L1014 IRS with the Submillimeter Array The Astrophysical Journal 633 2 L129 arXiv astro ph 0509865 Bibcode 2005ApJ 633L 129B doi 10 1086 498449 S2CID 14721548 Geballe T R Najarro F Rigaut F Roy J R 2006 TheK Band Spectrum of the Hot Star in IRS 8 An Outsider in the Galactic Center The Astrophysical Journal 652 1 370 375 arXiv astro ph 0607550 Bibcode 2006ApJ 652 370G doi 10 1086 507764 ISSN 0004 637X S2CID 9998286 Kuhn M A et al 2010 A Chandra Observation of the Obscured Star forming Complex W40 Astrophysical Journal 725 2 2485 2506 arXiv 1010 5434 Bibcode 2010ApJ 725 2485K doi 10 1088 0004 637X 725 2 2485 S2CID 119192761 Andre Ph et al 2010 From filamentary clouds to prestellar cores to the stellar IMF Initial highlights from the Herschel Gould Belt Survey Astronomy amp Astrophysics 518 L102 arXiv 1005 2618 Bibcode 2010A amp A 518L 102A doi 10 1051 0004 6361 201014666 S2CID 248768 M G Wolfire J P Cassinelli 1987 Conditions for the formation of massive stars Astrophysical Journal 319 1 850 867 Bibcode 1987ApJ 319 850W doi 10 1086 165503 C F McKee J C Tan 2002 Massive star formation in 100 000 years from turbulent and pressurized molecular clouds Nature 416 6876 59 61 arXiv astro ph 0203071 Bibcode 2002Natur 416 59M doi 10 1038 416059a PMID 11882889 S2CID 4330710 R Banerjee R E Pudritz 2007 Massive star formation via high accretion rates and early disk driven outflows Astrophysical Journal 660 1 479 488 arXiv astro ph 0612674 Bibcode 2007ApJ 660 479B doi 10 1086 512010 S2CID 9769562 I A Bonnell M R Bate C J Clarke J E Pringle 1997 Accretion and the stellar mass spectrum in small clusters Monthly Notices of the Royal Astronomical Society 285 1 201 208 Bibcode 1997MNRAS 285 201B doi 10 1093 mnras 285 1 201 I A Bonnell M R Bate 2006 Star formation through gravitational collapse and competitive accretion Monthly Notices of the Royal Astronomical Society 370 1 488 494 arXiv astro ph 0604615 Bibcode 2006MNRAS 370 488B doi 10 1111 j 1365 2966 2006 10495 x S2CID 15652967 I A Bonnell M R Bate H Zinnecker 1998 On the formation of massive stars Monthly Notices of the Royal Astronomical Society 298 1 93 102 arXiv astro ph 9802332 Bibcode 1998MNRAS 298 93B doi 10 1046 j 1365 8711 1998 01590 x S2CID 119346630 Retrieved from https en wikipedia org w index php title Star formation amp oldid 1048097460, wikipedia, wiki, book,

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