How the Milky Way Formed; Mysteries of the Milky Way; Exclusive Online Issues; by Sidney van den Bergh and James E. Hesser; 5 Page(s)

Attempts to reconstruct how the Milky Way formed and began to evolve resemble an archaeological investigation of an ancient civilization buried below the bustling center of an ever changing modern city. From excavations of foundations, some pottery shards and a few bones, we must infer how our ancestors were born, how they grew old and died and how they may have helped create the living culture above. Like archaeologists, astronomers, too, look at small, disparate clues to determine how our galaxy and others like it were born about a billion years after the big bang and took on their current shapes. The clues consist of the ages of stars and stellar clusters, their distribution and their chemistry--all deduced by looking at such features as color and luminosity. The shapes and physical properties of other galaxies can also provide insight concerning the formation of our own.

The evidence suggests that our galaxy, the Milky Way, came into being as a consequence of the collapse of a vast gas cloud. Yet that cannot be the whole story. Recent observations have forced workers who support the hypothesis of a simple, rapid collapse to modify their idea in important ways. This new information has led other researchers to postulate that several gas cloud fragments merged to create the protogalactic Milky Way, which then collapsed. Other variations on these themes are vigorously maintained. Investigators of virtually all persuasions recognize that the births of stars and supernovae have helped shape the Milky Way. Indeed, the formation and explosion of stars are at this moment further altering the galaxy's structure and influencing its ultimate fate.