Highly evolved: The white arrows point to a few of the old, massive galaxies at a distance of 10 billion light years. This cut-out image represents just 1/150th of the full survey.

Credit: UKIDSS UDS survey team

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SYDNEY: Old galaxies swathed in dark matter clustered together early in the history of the universe, and eventually evolved into the most massive galaxies known today, British scientists say.

The research, led by University of Nottingham PhD student Will Hartley, was presented earlier this week at the Royal Astronomical Society National Astronomy Meeting in Belfast, Ireland.

Using the United Kingdom Infra-Red Telescope (UKIRT) in Hawaii, the astronomers looked at old galaxies more than ten billion light years from our own. Because of the vast distances involved, these galaxies appear to us as they were four billion years after the Big Bang.

Surprisingly, the galaxies appear fully evolved, even at this relatively early stage in the history of the universe. Just why galaxies evolved so early is a question that has long puzzled astronomers.

Massive haloes

To find out, Hartley and his team analysed the way old galaxies clustered together. The gravitational pull between galaxies in a cluster shows how much invisible dark matter surrounds them, and hence reveals their mass.

All galaxies form within a halo of dark matter, mysterious 'stuff' that emits no radiation but has a gravitational effect. The haloes surrounding the old galaxies imaged by the UKIRT are extremely massive, containing material which is one hundred thousand billion times the mass of our Sun.

In the nearby universe, this sort of mass is found only in giant elliptical galaxies, the largest that we know of. Some elliptical galaxies are three to four times the size of our own spiral Milky Way galaxy, and between 50 to 100 times more massive.

Giant step

Hartley said their study provides a direct link to the present-day universe, and demonstrates that these distant old galaxies must evolve into the most massive but more familiar elliptical-shaped galaxies we see around us today.

"Understanding how these enormous elliptical galaxies formed is one of the biggest open questions in modern astronomy and this is an important step in comprehending their history," he added.

Astrophysicist John Dickey of the University of Tasmania, Australia, who has studied the evolution of galaxies and clusters, agrees the study is "very important and fundamental research".

"Conventional wisdom is that [elliptical galaxies] form from the merger of the building blocks of spiral galaxies," he said.

"Finding elliptical galaxies at high red shifts [further away from our own galaxy] suggests dark matter concentration formed very early in the history of the universe. Before this research, most people would have said clusters formed more recently," he said.