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

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 evolutio±I 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