Cannabaceae

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In astrophysics, photodissociation regions (or photon-dominated regions, PDRs) are predominantly neutral regions of the interstellar medium in which far ultraviolet photons strongly influence the gas chemistry and act as the most important source of heat.[1] They occur in any region of interstellar gas that is dense and cold enough to remain neutral, but that has too low a column density to prevent the penetration of far-UV photons from distant, massive stars. A typical and well-studied example is the gas at the boundary of a giant molecular cloud.[1] PDRs are also associated with HII regions, reflection nebulae, active galactic nuclei, and Planetary nebulae.[2] All the atomic gas and most of the molecular gas in the galaxy is found in PDRs.[3]

History

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The study of photodissociation regions began from early observations of the star-forming regions Orion A and M17 which showed neutral areas bright in infrared radiation lying outside ionised HII regions.[3]

References

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  1. ^ a b Hollenbach, D.J.; Tielens, A.G.G.M. (1999). "Photodissociation regions in the interstellar medium of galaxies". Reviews of Modern Physics. 71 (1): 173–230. Bibcode:1999RvMP...71..173H. doi:10.1103/RevModPhys.71.173.
  2. ^ Tielens, A.G.G.M. (1993). "Photodissociation regions and planetary nebulae". Planetary Nebulae: Proceedings of the 155 Symposium of the International Astronomical Union. 155: 155–162. Bibcode:1993IAUS..155..155T. doi:10.1017/S0074180900170330.
  3. ^ a b Hollenbach, D. J.; Tielens, A. G. G. M. (1997). "Dense photodissociation regions". Annual Review of Astronomy and Astrophysics. 35: 179–215. Bibcode:1997ARA&A..35..179H. doi:10.1146/annurev.astro.35.1.179.


source: https://en.wikipedia.org/wiki/Photodissociation_region

One thought on “Cannabaceae”

  1. Well, that’s interesting to know that Psilotum nudum are known as whisk ferns. Psilotum nudum is the commoner species of the two. While the P. flaccidum is a rare species and is found in the tropical islands. Both the species are usually epiphytic in habit and grow upon tree ferns. These species may also be terrestrial and grow in humus or in the crevices of the rocks.
    View the detailed Guide of Psilotum nudum: Detailed Study Of Psilotum Nudum (Whisk Fern), Classification, Anatomy, Reproduction

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