Physics Colloquium - Friday, Apr. 18th, 2008, 4:00 P.M.

E300 Math/Science Center; Refreshments at 3:30 P.M. in Room E200

Jeff Hester
School of Earth & Space Exploration
Arizona State University

Born Among Giants: The Solar System's Violent Origins

Studies of the formation of low-mass stars such as our Sun have long focused on regions such as the nearby Taurus-Auriga molecular cloud. Located at a distance of only 140 parsecs (about 450 light years), Taurus offers our best opportunity to study young stellar objects and their environments up close. In this small dark cloud, stars form in relative isolation, and for the most part shape their own fate. It is this relatively quiescent environment that has long shaped our thinking about the origins of our own Solar System. Recently, however, studies of the decay products of short-lived radionuclides in meteorites have radically altered that picture. 60Fe, in particular, is a neutron-rich isotope that cannot be produced by any known processes that take place in an isolated protoplanetary disk. The only astrophysically plausible source for 60Fe is the explostion of a massive star - a core collapse supernova - that must have occurred in close proximity to the Sun very near the time it was born. The implication of these results is clear. Rather than forming in isolation, the Sun, like most low-mass stars, formed in a large cluster containing massive stars. The region around a massive star is a violent place where intense radiation, supernovae, and other forms of energy input from massive stars reshape the medium and dominate the processes at work there. In particular, the ongoing process of star formation and the evolution of protoplanetary disks is altered in fundamental ways. Star formation is triggered, then terminated by dispersal of molecular material. Protoplanetary disks are eroded by photoevaporation, and then subjected to blast waves from supernovae. Short-lived radionuclides from supernovae are injected into the circumstellar environments of young stars where their decay may provide the dominant source of power to heat newly formed planetesimals. Indeed, the young Sun's interstellar environment altered virtually every aspect of the evolution of the young Solar System. In this talk I will discuss the process of low-mass star formation around massive stars, consider the evidence that places the Sun in such an environment, then close with a few ideas about why this all matters to our understanding of our own origins.