FROM DARKNESS TO LIGHT - FORMING THE OLDEST STARS IN THE COSMOS


Penticton, BC: Astrophysicists are announcing the results of new computer simulations on how and when the first star clusters in the universe may have formed. The report is being presented by Dr. Ralph E. Pudritz of McMaster University in Hamilton (Ontario) to the Canadian Astronomical Society Meeting in Penticton, B.C. Dr. Pudritz and his collaborator, Dr. Melinda Weil (City College of San Francisco), have found that giant cold, gas clouds up to a thousand times more massive than any observed in our Milky Way, formed within young galaxies when they were only a billion years old. These massive star factories are of special interest because they are the likely site for the formation of the oldest star clusters known in the universe - the globular star clusters.

Their computer simulations, carried out on computers in the U.K. as well as at McMaster University, begin with standard models for cosmology. These models posit that fluctuations in the background density of matter in the universe grow with time, eventually becoming massive enough to be the seeds for the formation of galaxies such as our own. The collapse of gas into these overdense and low-masss fore-runners of the present day galaxies and the subsequent formation of cool clouds that are bound by their own gravitational attraction, may produce these massive nurseries for the first stars, and star clusters in the universe. The researchers tuned their simulations so that they could study the evolution of these clouds in greater detail than most existing computer simulations.

Their findings are startling: so-called supergiant clouds (SGMCs) form as smaller gas clouds in young galaxies collide and stick. The mass-spectrum of these supergiant clouds is identical to the mass spectrum that we see for the cradles of star formation in our own galaxy, namely the Giant Molecular Clouds (GMCs). The main difference is their size - 1 kiloparsec for SGMCS and only 10s of parsecs for GMCs, as well as their mass - only a millions times the mass of the sun for GMCs, and up to a billion times the mass of the sun for the SGMCs.

Another major result of this work is that these supergiant nurseries for the globular clusters have no difficulty in forming in different cosmological models. While cosmologists are learning a great deal about the structure and age of the universe from a variety of observations, there still is some latitude in the exact cosmology that governs our universe. Pudritz and Weil show that supergiant clouds would nonetheless form in galaxies within different cosmological models. The main difference between these is the exact age the universe would be when the first of the globular clusters was actually born and achieved "first light". The new results presented today focus on the cosmological most favoured by current observations - namely, one in which the expansion of the universe is accelerating with time.

"Our findings suggest that the formation of the first star clusters in the universe was not too different in character from the formation of star clusters what we see nearby to us in the Milky Way - such as the famous Trapezium star cluster in the Orion Nebula." states Ralph Pudritz. The main difference he says, is that ".. the Orion star cluster is a dwarf by comparison - thousands of Orion clusters could neatly fit into a globular star cluster". Their research builds on the efforts of many cosmologists who constructed computational tools with which the evolution of the galaxies in the early universe can be charted. It also encompasses a great dealthat has been learned about the process of star formation over the last decade.

This research was supported by the Natural Science and Engineering Research Council of Canada, McMaster University, and the City University of New York (CUNY).

For more information contact:

Dr. Ralph Pudritz
Dept. of Physics and Astronomy
McMaster University,
Hamilton, ON L8S 4M1
Phone: (905) 525 9140 ext 23180
FAX: (905) 546 1252
Email: pudritz@physics.mcmaster.ca