Research

ISM and Star Formation

Description

An understanding of how stars form is of central importance to many areas of astronomy, ranging from searches for planets to observations of the distant universe. Theoretical and observational work on star formation at Yale has concentrated on several major aspects of the problem, including the fragmentation of collapsing gas clouds, the role of outflows and disks in star formation, the evolution of star-forming cores, the origin of binary and multiple systems, and the formation of star clusters. A central issue in this subject has been the need to understand the factors that determine stellar masses and the stellar Initial Mass Function (IMF). Observational studies have shown that stars have a characteristic mass similar to the mass of the Sun, which may be understandable theoretically in terms of the expected mass scale for cloud fragmentation. However, the IMF also has a long tail extending to much higher masses, and the formation of massive stars and the origin of the upper IMF are not yet well understood; this is one of the present frontier areas of research on star formation. Both theoretical and observational work on this topic is currently being carried out at Yale.

An important topic in this field is understanding the chemical processes that take place during different stages of star formation. As the core evolves from a dense pre-stellar condensation to an unbound, low-density, concentration of gas surrounding the young star, the chemistry of the protostellar environment changes. Different physical processes at different evolutionary stages trigger varying chemical reactions. And, the chemistry of cores is very likely to reflect directly in the molecular composition of the circumstellar disks and eventual proto-planets of the system. Knowledge of the chemistry in protostellar environments is required to fully understand the physical process that take place during star formation. Some of the current observational work at Yale University is aimed at understanding the chemical evolution of cores, deducing how different physical processes affect the chemical status of the circumstellar gas and determining the reliability of using chemistry as a protostellar clock.

Another subject of great current interest is star formation in the very early universe, which may soon become observable at high redshifts. Theoretical arguments suggest that early star formation might have favored massive stars, and these stars would have been important sources of energy and heavy elements for the early universe. Recent work at Yale has modeled numerically the formation of the first stars from primordial gas uncontaminated with heavy elements, which had not yet been created by stellar nucleosynthesis. These calculations predict a mass scale for cloud fragmentation that is much larger that the mass of the Sun, and this suggests that the first stars were indeed very massive and would have had important effects on the early universe and on galaxy formation. Future instruments may be able to observe systems of such stars directly at high redshifts, providing a link between star formation studies and research on cosmology and galaxy formation.

More information and lists of relevant publications can be found in these sites: Hector Arce's Research page and Richard Larson's Research page.

Image Credits: (header) NASA, ESA, J. Hester and A. Loll (Arizona State University)

Yale University

© 2014 Yale University. All Rights Reserved.

Members

Group Members

H├ęctor Arce

Associate Professor, Astronomy

Web Site | Please visit my homepage

E-mail |

Phone | (203) 432-3018

Fax | (203) 432-5048

Michael Faison

Lecturer, Director of Leitner Family Observatory at Yale

Web Site | Please visit my homepage

E-mail |

Fax | (203) 432-5048

Richard B. Larson

Professor Emeritus of Astronomy

Web Site | Please visit my homepage

E-mail |

Phone | (203) 432-3015

Fax | (203) 432-5048

Yale University

© 2014 Yale University. All Rights Reserved.