Baby Milky Way Modeled

This snapshot of a state-of-the-art simulation shows the flow of gas into a fledgling galaxy.

By Ron Cowen, Science News

BLOIS,  France — Like a proud papa  showing off a picture of his newborn, cosmologist Ben Moore of the University of Zurich  in Switzerland  displayed an image of a galaxy that he says looks just like a newborn Milky  Way. These days, with the sharp eye of Hubble and other telescopes, that may  not sound like much of a feat. But the image Moore unveiled June 22 at the Windows on the  Universe meeting was produced in a supercomputer and is the highest-resolution  simulation ever attempted of a galaxy’s assembly.

Moore and his colleagues put in all the raw  ingredients and detailed interactions that are generally agreed to be essential  for galaxy formation. The simulation incorporates a halo of dark matter — the  invisible material that provides the scaffolding for pulling together visible  material — as well as hydrogen and helium gases and forces acting on these  materials, such as shock waves from exploding stars.

“The complexity we find is very beautiful,”  Moore says. As  time unfolded, the simulation, which begins shortly after the Big Bang and ends  when the universe is about 2 billion years old, produced a real-looking spiral  galaxy, akin in mass and shape to a young Milky Way.

“For the first time we’ve resolved individual  molecular clouds, the hot [dark matter] halo and cold streams of gas that  travel like a river” along dark matter filaments into the center of the  fledgling galaxy, Moore  says. The cold gas turns out to be essential for forming the bulge of stars at  the galaxy’s core.

The model isn’t perfect, Moore notes. It produces a stellar bulge that  is about three times as massive as the Milky Way’s.

Video: This movie models how a galaxy acquires most of its gas — the raw material for making stars. Red is hot gas, blue shows the cold streams of gas that flow like a river toward the galaxy’s center, and green shows gas that has been stripped out of satellite galaxies and enriched in metal content by supernova explosions.

Credit: B. Moore, Oscar Agertz and Romain Teyssier/University of Zurich