Interstellar matter

About a hundred years ago, it was still thought that interstellar space was completely empty, except for the cosmic nebulae, which were already known at that time. The presence of matter in interstellar space was shown by the fact that in certain regions of the sky, light from distant stars was either scattered or absorbed in other words, dark, star-free regions are present. 

The mean particle density of ISM is 106 particles per cubic meter there are, however, great variations from this mean value. Between the spiral arms of the Milky Way, there are between 104 and 105 hydrogen atoms per cubic metre in the dark clouds and the HII regions, there are 10s—1010. Up to 1012—1014 hydrogen atoms per cubic metre are present in regions with OH sources and in certain infrared objects. 

Interstellar matter (ISM) consists mainly of gaseous components, with only a minor fraction existing in particulate form. These few particles, however, cause the light from the stars to be blotted out, as they interact much more strongly with the visible light than do molecules or atoms in the gaseous state. Spectroscopic observations also point to the existence of ISM Fig. 3.10 gives a survey of the distribution of cosmic matter. 

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The dark clouds were responsible for the discovery of ISM, as they absorb the light from stars which lies behind these clouds of interstellar matter. It is difficult to obtain reliable information on the dust particles. They are probably about 0.1 pm in diameter, consisting of a silicate nucleus and an envelope of compounds containing the elements C, O and N, which, with H and He, are the main elements present in interstellar space. There are only two sources of information for more exact characterisation of the dust particles ... 

Thus, there is a great deal of information on the reaction potential of HCN and products derived from it. Gaps in our knowledge may perhaps be closed in the next few years by research results on the chemistry occurring on other planets or in interstellar matter. As early as 1984, Jim Ferris published a review article HCN and... 

The phosphorus chemistry occurring in interstellar matter and in the circum-stellar regions of the cosmos is not yet understood. We do, however, know that phosphorus compounds are present in meteorites, lunar rocks and Mars meteorites. Oddly enough, the element can be detected nearly everywhere, though only in low concentrations. Phosphate minerals, as well as the anions PO2 and PO3, have... 

A second example of an explosion remnant is the fine lacework of the Cygnus loop, located 2500 light-years from Earth. In supersonic expansion, the gas produces shock waves that excite and ionise interstellar matter, causing it to glow. 

We may wonder what effect these gigantic explosions and accompanying radiation may have on the galactic environment of the hypernova. Such an energy release could only produce holes, hollow shells in the distribution of interstellar matter. After 1 million years, these cavities reach a radius of 150 to 500 light-years, according to calculation. The initial excesses are followed by a calmer expansion at speeds below 10 km s ... 

Simulated interstellar matter, such as forsterite, enstatite and magnesite, has been irradiated by gamma-rays and fast neutrons and their induced spectra have been investigated. For the forsterite and magnesite after irradiation the spectra exhibit rather intensive peaks at approximately 650 and 660 nm, respectively. Besides that, forsterite demonstrates several narrow lines the strongest one at 610 nm (Koike et al. 2002). 

Within some meteorites are also found minuscule presolar grains, providing an opportunity to analyze directly the chemistry of interstellar matter. Some of these tiny grains are pure samples of the matter ejected from dying stars and provide constraints on our understanding of how elements were forged inside stars before the Sun s birth. Once formed, these... 

The term cosmochemistry apparently derives from the work of Victor Goldschmidt (Fig. 1.6), who is often described as the father of geochemistry. This is yet another crossover and, in truth, Goldschmidt also established cosmochemistry as a discipline. In 1937 he published a cosmic abundance table based on the proportions of elements in meteorites. He used the term cosmic because, like his contemporaries, he believed that meteorites were interstellar matter. Chemist William Harkins (1873-1951) had formulated an earlier (1917) table of elemental abundances - arguably the first cosmochemistry paper, although he did not use that term. As explained in Chapter 3, the term solar system abundance is now preferred over cosmic abundance, although the terms are often used interchangeably. 

If the 244Pu/238U ratio in the fresh supernova debris is P and that in the interstellar matter (old debris) is Q, the initial Pu/238 ratio (a) in the mixture of matter from which the solar system was formed is... 

Observations of isotopic abundances provides information on the nucleosynthesis operating in the compact core of stars and supernova explosions and on the chemical evolution of the Galaxy. The CNO nuclides in late-type stars are affected by freshly synthesized core material brought up by dredge-up events. On the other hand, the Si isotopes are involved in later phases of nuclear burning, a narrow span of the red giant lifetime before planetary nebulae or supernovae. Therefore relative abundances of Si isotopes we observe remain unchanged from those of interstellar matter from which a star was formed. 

The N-protonated form of HNSi, the H2NSi+ cation 69 and its possible isomers have been studied extensively by theoretical methods230-234. Bohme47 suggested that the ion 69, which is formed upon reaction of silicon cations with ammonia and subsequent dissociation of 69 upon electron capture (equation 33)235, is of prime importance for the formation of Si—N bonded species such as 67 in the chemistry of interstellar matter. 

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