THE EXPLODING SUNS

An honest-to-goodness new Asimov book: not a swatch of columns, an array of editings, or a one-volume explanation of everything. It's about novas and supernovas, the glamorous starbursts that have inspired not a few popular books over the decade. As usual, Asimov brings to his coverage chronological detail, a bare minimum of personalities, and a zeal to explain complexities to lay audiences. So we learn that novas are those wild explosions that result from the exchange of matter between ultraclose stars: one, a white dwarf normally on the road to oblivion; the other, a main sequence star moving up to red giant status but throwing off matter to enrich its neighbor in an accretion ring. Supernovas, on the other hand, fall into two types—the more interesting of which are the type IIs: massive stars that pass through white dwarfery on their way to becoming neutron stars (pulsars) and possibly even black holes. In the process, the supernovas spew out outer layers so heated and charged with energy as to produce the nuclei of massive elements, to seed the cosmic dust. Like others, Asimov says we must thank our lucky supernovas for endowing space with the particles that allow a second generation star, like our sun, to form with all the debris necessary to supply a planetary system with the wherewithal of life. Following his good exposition of the novae, indeed, Asimov takes up cosmic, earthly, and biological origins, evoking the useful fallout from supernovae in these processes. There's discussion of new millisecond pulsars not found elsewhere, and of the role of supernovas in triggering star formation, and providing strong sources of cosmic rays. True to Asimov form, there is also conjecture of probabilities should a supernova burst nearby. A skillful job.