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A protostar (from Greek protos = the first) is an area within a collapsing interstellar cloud that has already almost reached hydrostatic equilibrium and eventually becomes a star through a steady, gravitational increase in mass from the surrounding cloud . During its slow collapse, a protostar converts gravitational energy into heat, which is given off as infrared radiation .

Origin and further development

Infrared image of a cloud of matter in which stars are forming

The prerequisite for the formation of stars is the presence of comparatively dense, cool clouds of matter, so-called molecular clouds . Such clouds consist of around 70% molecular hydrogen (H 2 ) and much smaller parts of other molecules such as carbon monoxide (CO), silicate and graphite particles. In order for protostars and ultimately stars to develop in molecular clouds, the molecular clouds must meet the Jeans criterion . The Jeans criterion (after the English mathematician and physicist James Hopwood Jeans ) specifies the mass a cloud must have in order for it to collapse at a certain temperature and density. A large mass and a low temperature are advantageous for star formation. If the Jeans criterion is fulfilled in individual areas in a molecular cloud, these collapse and the molecular cloud breaks up into several partial clouds (fragmentation). These fragments can in turn break down into further, smaller fragments, the density of which increases further and further.

When a certain density of a partial cloud is reached, the radiation can no longer leave the cloud unhindered. This causes the central area of ​​the cloud to heat up and the temperature and pressure to rise. The core enters a first almost hydrostatic state. The cloud now consists of a first core with a thin gas envelope that surrounds the core.

What follows now is the so-called Kelvin-Helmholtz contraction phase , which is much slower than before. During this phase, matter continues to fall from the shell onto the protostar and thus ensures a further increase in mass ( accretion ) and a rise in temperature, so that hydrogen and helium are ionized in the core. Through this process the core loses a lot of energy, so that temperature and pressure cannot rise any further. This allows the cloud to collapse a second time, which only comes to a standstill when all atoms are fully ionized. A quasi hydrostatic state occurs again with a "second" core. As soon as the quasi hydrostatic equilibrium is established, one speaks of a protostar.

The accretion continues until all matter has fallen into the core. When the matter has completely fallen onto the nucleus and the molecular gas is completely ionized, the protostar reaches the Hayashi stage. Since the research results of the astrophysicists Hayashi and Nakano, one no longer speaks of protostars, but of "young stars" or "pre-main sequence stars", which are further subdivided into " T-Tauri stars " and " Herbig-Ae / Be stars ".

Protostars and then young stars continue to contract until the temperature inside them exceeds 3 million Kelvin , causing the hydrogen to burn and the radiation pressure to stabilize the star. The star is now born and moves to the main sequence .

Position on the Hertzsprung-Russel diagram

In the Hertzsprung-Russel diagram , the state of a collapsing gas cloud is initially to the right of the Hayashi line and approaches it. One speaks of a protostar when the state of the gas cloud has reached the Hayashi line and the hydrostatic equilibrium is established.

Examples of observed protostars

The researchers Philippe Andre, Derek Ward-Thompson and Mary Barsony found the youngest star ever observed at about 10,000 years , according to a report in New Scientist magazine on February 20, 1993. The protostar, labeled VLA 1623 , was tracked down with the James Clerk Maxwell Telescope in Hawaii .

On July 10, 2013, ESO announced that it had discovered the largest protostar to date in the Milky Way with the ALMA telescope in Chile, which currently has a mass of 500  solar masses . The still growing and so far nameless celestial body is 11,000  light years away in the dark cloud Spitzer Dark Cloud 335.579-0.292 .

Another example of an observed protostar is W75N (B) -VLA2 , also called VLA2 or Very Large Array 2, a protostar in the star cluster W75N (B), which is 4,200 light years from Earth.

See also


  • Norbert Langer: Life and Death of the Stars . Beck, Munich 1995, ISBN 3-406-39720-4 .
  • Harald Lesch, Jörn Müller: Stars. How light comes into the world , 2nd edition. Goldmann, Munich 2011, ISBN 978-3-442-15643-6 .
  • Steven W. Stahler, Francesco Palla: The Formation of Stars . Wiley-VCH, Weinheim 2004, ISBN 3-527-40559-3 .
  • VG Surdin, SA Lamzin: Protostars . How, where and what do stars come from? Barth, Heidelberg / Leipzig 1998, ISBN 3-335-00444-2 .

Web links

Commons : Protostars  - Collection of images, videos, and audio files

Individual evidence

  1. Harald Lesch, Jörn Müller: Stars . 2nd Edition. Goldmann, Munich 2011, ISBN 978-3-442-15643-6 , pp. 94-102 .
  2. Harald Lesch, Jörn Müller: Stars . 2nd Edition. Goldmann, Munich 2011, ISBN 978-3-442-15643-6 , pp. 110-112 .
  3. VG Surdin, SA Lamzin: protostars . Barth, Heidelberg / Leipzig 1998, ISBN 3-335-00444-2 , p. 131-132 .
  4. VG Surdin, SA Lamzin: protostars . Barth, Heidelberg / Leipzig 1998, ISBN 3-335-00444-2 , p. 146 .
  5. Anna Frebel: In search of the oldest stars . Fischer, Frankfurt a. M. 2012, ISBN 978-3-596-19191-8 , pp. 113 .
  6. Ludwig Bergmann, Clemens Schaefer: Textbook of Experimental Physics, Volume 8: Stars and Space , 2nd edition. De Gruyter, Berlin 2002, ISBN 978-3110168662 , pp. 252-253.
  7. Student blogs Physics: Star formation . Website of the Georg-August-Universität Göttingen. Retrieved August 18, 2018.
  8. Stuart Clarke: Science: Youngest star . In: New Scientist, February 20, 1993. Retrieved August 18, 2018.
  9. Deutschlandfunk , Forschungs aktuell : Astronomers have discovered the formation of a giant monster protostar in the Milky Way . Retrieved August 18, 2018.
  10. ESO : ALMA Prenatal Scan Reveals Embryonic Monster Star . Retrieved August 18, 2018.
  11. C. Carrasco-González et al. a .: Observing the onset of outflow collimation in a massive protostar . In: Science 348, 2015, pp. 114–117. ( Abstract )