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(5) Explanation of chemical evolution in the universe

As expected, ASCA is successfully detecting the X-ray emission lines of the ions of heavy elements in celestial bodies of various levels of organization, including supernova remnants, individual galaxies, and galaxy clusters.

Observations of supernova remnants are successful in clearly distinguishing that the remnants of type I supernovae are rich in iron and the remnants of type II supernovae are rich in oxygen and silicon. Thus the supernova theory is being proven with good accuracy.

Observations of galaxies and galaxy clusters are showing that the heavy elements created by nuclear fusion in fixed stars are expelled by supernova explosions and other causes, and scattered through interstellar space.

Observations are also clarifying the circumstances of their discharge into intergalactic space. It has been made clear that the products of type II supernovas are more plentiful in large-scare galaxy clusters and that the proportions of type I and type II supernova products are about the same in small-scale galaxy clusters.

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ISAS/JAXA Department of High Energy Astrophysics