Shining a light on stars

Sep 14 2007 by Tony Henderson, The Journal

COSMOLOGISTS in the North-East have revealed the results of a groundbreaking study which has provided new insights into the way the first stars were formed at the start of the universe around 13bn years ago.

The experts from Durham University suggest that the formation of the first stars depended crucially on the nature of “dark matter”, the material that makes up most of the mass in the universe.

The discovery takes scientists a step further to determining the nature of dark matter, a mystery since it was first discovered more than 70 years ago. It also suggests that some of the very first stars that formed can still be found in the Milky Way galaxy today.

After the Big Bang, the universe was mostly “smooth”, with just small ripples in the matter density.

These ripples grew larger due to the gravitational forces acting on the dark matter particles contained in them. That eventually led to the formation of the very first stars, about 100 million years after the Big Bang.

For their research, the team from the university’s Institute for Computational Cosmology carried out sophisticated computer simulations of the formation of these early stars with accepted scientific models of so-called “cold” as well as “warm” dark matter.

They found that for slow moving cold dark matter particles, the first stars formed in isolation. In contrast, for faster-moving warm dark matter, a large number of stars of differing sizes formed at the same time in a big burst of star formation. The bursts occurred in long and thin filaments.

One of the researchers, Dr Liang Gao, who receives funding from the UK’s Science and Technologies Facilities Council, said: “These filaments would have been around 9,000 light years long, which is about a quarter of the size of the Milky Way galaxy today. The very luminous star burst would have lit up the dark universe in spectacular fashion.”

Stars forming in the cold dark matter are massive, about 100 times the mass of the Sun.

The larger a star is, the shorter its life span, so these larger mass stars would not have survived until today. However the warm dark matter model predicts the formation of low mass stars as well as larger ones, and the scientists say the low mass stars would survive.

Co-researcher Dr Tom Theuns said: “A key question astronomers often ask is where are the descendants of the first stars today? The answer is that, if the dark matter is warm, some of these primordial stars should be lurking around our galaxy.”

The Durham team also give new insights into the way that black holes could be formed.