dwarf-galaxies

A simulated dwarf galaxy is seen at six different stages of its evolution, with the top-left image representing one billion years after the Big Bang and the bottom right showing the present day. The dark spots and circles in the images are caused by massive exploding stars. ((Katy Brooks))

Exploding supernovas and the resulting "winds" were vital in the formation of today's galaxies, says an international team of astronomers.

Scientists from the U.S., Canada, U.K. and Switzerland collaborated on the study, appearing this week in the journal Nature, that used millions of hours of supercomputer time to simulate the evolution of the universe.

The research was undertaken to address a problem in the prevailing theory of galaxy formation, called the cold dark matter theory, first conceived in the 1980s.

Previous simulations based on the theory have suggested that galaxies should have more stars than they actually do, especially so-called dwarf galaxies, which have less than one per cent of the stars found in galaxies like our Milky Way.

Fabio Governato, an associate professor of astronomy at the University of Washington and lead author of the study, says previous simulations haven't included a detailed description of how stars form and die.

"We performed new computer simulations, run over several national supercomputing facilities, and included a better description of where and how star formation happens in galaxies," said Governato, in a statement.

Those supercomputer facilities included the SHARCNET computers at McMaster University in Hamilton, Ont.

'More accurate simulations'

What the scientists found in the simulation was that massive stars exploding in supernovas generated stellar winds, pushing enormous amount of gas out of the centre of galaxies.

The expulsion of gas prevented millions of new stars from forming, consigning the galaxy to drawf status.

The supernova explosions were the missing piece of the puzzle, the researchers said, and their simulation supports the cold dark matter theory.

"The cold dark matter theory works amazingly well at telling where, when and how many galaxies should form," Governato said.

"What we did was find a better description of processes that we know happen in the real universe, resulting in more accurate simulations," he said.

The theory of dark matter holds that most of the matter in the universe — as much as 75 per cent — is dark material that can't be observed in the electromagnetic spectrum. "Cold" in this case refers to particles following the Big Bang that have speeds much lower than the speed of light.

In the cold dark matter theory of galaxy formation, clumps of matter coalesce into structures that eventually form massive halos, and galaxies form within the halos.