Interstellar Environment

In Astronomy, the interstellar environment is mainly the rarefied Gaz which, in a Galaxie, exists between the star S and their close environment. This gas is usually extremely thin, with typical densities of matter going from 10 to 100 particles per cubic decimetre (or Liter). One also includes under the interstellar denomination medium the planetary Nébuleuses, the envelopes of Nova E and Supernova E and the environment of the active cores of galaxies. In these cases the densities are higher (to 100000 particles per Cm3).

Generally this gas is roughly made up of 90% of Hydrogène and 10% of Hélium; the others elements, which the astronomers call of the “metals”, are present only in the form of traces. Molecules are also observed in the interstellar environment (molecular clouds), most abundant are H2 and CO. Were also observed OH, H2O, CN, CS, HCN, H2CO and hundreds of others (in particular in the Nébuleuse of Orion). Molecules even more massive are deferred: C60 (Fullerene), of HAP, the Amino-acid inter alia.

There exist also interstellar dust (solid phase) in addition to the gas (approximately 1% of the total mass of interstellar environment).

The interstellar environment is usually divided into three phases, according to the temperature of gas: very hot (million Kelvin), hot (thousands of Kelvin) and cold (tens of Kelvin). This model in three phases was developed by Chris McKee and Jerry Ostriker in an article published in 1977 and which was used as a basis for the studies undertaken during the 25 years which followed. The relative proportions of these phases is still matter with discussion in the scientific circles.

The main subjects of study of the interstellar environment are: the molecular clouds, the interstellar clouds, the areas HII, remanent of supernova, the planetary nebulas as well as other diffuse structures.

The interstellar environment remains still today a complex subject of research, as well on the level of the physics as of chemistry which is held there. More and more, the studies carried out take into account these two aspects to try to explain abundances of the elements observed in the interstellar environment. Among these sets of themes of research, one can quote the models of shocks of David Flower and Guillaume Pineau of the Drills and the models of dissipation of the turbulent energy of Edith Falgarone.

Advanced in the study of the interstellar environment

  • 1848 : Lord Rose studies M1 and names it Nébuleuse Crab
  • 1864: William Huggins studies the spectrum Nébuleuse of Orion and proves that it is a gas cloud
  • 1927: Ira Bowen explains the spectral lines not identified as a prohibited lines of transition
  • 1930: Robert Jules Trumpler discovers absorption by the interstellar dust by comparing the apparent size and the globular luminosity of Amas S
  • 1944: Hendrik van of Hulst predicts the existence of the hyperfine Raie of 21 centimetres of neutral interstellar hydrogen
  • 1951: Harold Ewen and Edward Mills Purcell observes the hyperfine line of 21 centimetres of neutral interstellar hydrogen
  • 1956: Lyman Spitzer predicts the existence of Gaz coronal around the Milky Way
  • 1965: James Gunn and Bruce Peterson uses the observation of the relatively weak absorption of the blue component of the line Lyman alpha of 3C9 for strongly forcing the Densité and the state of Ion isation of the intergalactic Milieu
  • 1969: Lewis Snyder, David Buhl, Ben Zuckerman and Patrick Palmer discover interstellar Formaldéhyde
  • 1970: Arno Penzias and Robert Wilson discovers interstellar Carbon monoxide
  • 1970: George Carruthers observes molecular hydrogen in the space
  • 1977: Christopher McKee and Jeremiah Ostriker proposes a theory of the interstellar medium composed of three phases

See too

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