From the Atom to the Universe: Recent Astronomical Discoveries

Abstract

JEREMIAHP. OSTRIKER, a Fellow of the American Academy since 1975, is the Charles A. Young Pro fes sor Emeritus of Astrophysics at Prince ton University and Professor of As tronomy at Columbia Univer sity. His research interests concern dark matter and dark energy, gal axy formation, and quasars. His publications include Heart of Dark ness: Unraveling the Mysteries of the Invisible Universe (with Simon Mitton, 2013) and the volumes Formation of Structure in the Universe (edited with Avishai Dekel, 1990) and Un solved Problems in Astrophysics (edited with John Bahcall, 1997). He was the recipient of the U.S. National Med al of Science in 2000. Astronomy starts at the point to which chemistry has brought us: atoms. The basic stuff of which the planets and stars are made is the same as the terrestrial material discussed and analyzed in the 1⁄2rst set of essays in this volume. These are the chemical ele ments, from hydrogen to uranium. Hydrogen, found with oxygen in our plentiful oceanic water, is by far the most abundant element in the universe; iron is the most common of the heavier elements. All the combinations of atoms in the complex chem ical com pounds studied by chemists on Earth are also possible components of the objects that we see in the cos mos. Although almost all of the regions that we astronomers study are so hot that the more com pli cated compounds would be torn apart by the heat, some surprisingly unstable organic molecules, such as cyanopolyynes, have been detected in cold re gions of space with very low density of matter. Nev ertheless, the astronomical world is simpler than the chemical world of the laboratory or the real bio log ical world. But the enormous spatial and temporal extent of the cosmos allows us–and in fact forces us–to ask questions that would seem offbeat to a chemist. Where do the chemical elements come from? Precisely how, where, and when were they made? Do the abundances of the elements change with time? Does alternative “matter” that is not made of the or dinary chemical elements exist and exert gravity in the universe? We in the trades of astronomy and as trophysics must ask ourselves these ques tions–and they are only the beginning.