Making stars in early galaxies
(Phys.org)—Ten billion years ago or so, at least according to the current picture, the youthful universe began to produce an abundance of new stars. The very first ones appeared in the young cosmos after only a few hundred million years, but they were unlike stars of today. The universe back then contained almost no elements other than hydrogen (and some helium), and so these first stars contained mostly hydrogen and were very massive. By the time a few billion years had passed, however, this first generation of stars had manufactured many other elements that enriched the natal gas. These elements could help the gas cool as it compressed, and so they aided gravity as it collapsed material to form a wide range of new stars, many of them similar to the Sun. After a few billion years, galaxies acquired their mature forms and were populated by nearly normal stars. Then,...