Supernova dust

The Allende, Murchison, Murray and Orgueil meteorites are particularly highly prized for research into stellar grains, since several kilograms of this material have been identified in each of them. This is sufficient to be able to take samples of the order of 1 g without damaging the source. Such samples can then be subjected to compositional analysis. But how can we extract these stellar jewels, measuring at most 1 /rm in diameter, from the matrix in which they are embedded The best way of finding a needle in a haystack is to bum the hay. Cosmochemists employ basically the same method when they use chemical processes to isolate star dust trapped in meteoritic stone. They may then analyse 

Isotopic ratios such as the ratio of carbon-12 to carbon-13, corrected for physicochemical enrichment or impoverishment, are imputed to purely nuclear, and hence stellar, processes. 

The different types of grain can be related to specific classes of stellar objects. The very hot and bright, even lavish Wolf-Rayet stars are considered to be one of the most favourable sites for grain formation, for their strong stellar winds are particularly rich in carbon. Matter thrown out by supernovas and cooling very quickly due to its expansion is also an excellent scenario for grain formation. Elements with any affinity for the solid state are likely to be abundantly transformed. 

It was indeed a pleasant surprise to discover that certain grains carrying the unmistakable signature of supernovas had survived the turbulent formation of the Solar System. In addition it proved possible to extract them from meteorites without modifying them, so that they could be studied at leisure in terrestrial laboratories. Dissolving the stony component in acid and carrying out a series 

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The interstellar medium is the medium that fills the space between the stars. This space is far from empty. It includes magnetic fields, gas composed of atoms and ions at several different temperatures and densities, cosmic rays, and dust particles. The material content of the ISM changes with time owing to the formation of new stars from it and the ejection of matter from stars into it. The latter include the new nuclei thathave just been assembled by nucleosynthesis in the stars. The state of this medium is turbulent, driven by the shock waves from exploding supernovae. Dust comprises about one percent of the mass of the interstellar matter. It is measured by its infrared radiation and by its obscuration and reddening of starlight. 

Another view, equally consistent with the source abundances and better suited to account for the abundance of light elements like beryllium in stars of the Galactic halo (see below), is that dust particles in the supernova ejecta are the source of ions that are preferentially accelerated within the hot, tenuous gas of superbubbles surrounding regions of star formation (Lingenfelter, Ramaty Kozlovsky 1998). 

The second interesting feature of this isotope is that minuscule grains of silicon carbide extracted from meteorites have been found to be very rich in calcium-44, as mentioned earlier. They have been identified with presolar grains that condensed in the ejecta of supernovas during their first few years of expansion. Could it be that supernovas have been throwing sand in our eyes Data gathered by the ISO (Infrared Space Observatory), yet another experiment with strong participation by the French CEA, clearly demonstrates that new dust condensed inside the Cas A remnant very soon after explosion of the supernova that caused it. °... 

Spectropolarimetric monitoring is being carried out on the Anglo-Australian telescope by Cropper et al. (1987). The initial continuum polarisation was about 0.8%, but this subsequently decreased. However, the polarisation in the lines, particulary in the absorption component of Ha has increased sharply. Since the polarisation is determined by the interstellar dust, the shape of the supernova fireball and the scattering processes in the photosphere, these results are difficult to interpret However, they can provide us with very useful modelling constraints. 

Well, our Sun takes about 30 million years to incubate as a protostar and form a mature sun. Stars three times the mass of our Sun might take just a million years to be born, and stars one tenth the size of our Sun might emerge in about 100 million years. Protostars are just dense clouds of gas and dust. Remember, a supernova triggers their gravitational collapse into a star (figures 7.2 and 7.3). 

That s the only way to get a lot of carbon out of the star and into space. But supernovas can t be too common or else they would destroy too many worlds. On the other hand, as I mentioned before, supernovas are important because the shock waves they produce can cause planetary systems to start to coalesce from dust clouds surrounding other stars. This means that there can t be too many supernovas or too few. Any substantial deviation would decrease planetary formation and the emergence of life. ... 

Gaseous components of molecular clouds tend to condensate on the surface of solid dust particles at low temperatures. These dust particles are produced in the atmospheres of cool giant stars by condensation of refractory materials such as olivine and other silicates, whereas condensation of supernova ejecta results in metallic particles. 

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