In the Hunt For Dark Matter, New Simulations Show Evolution Of “Local Universe”

Brett Smith for – Your Universe Online

According to astrophysicists, dark matter is the key to understanding the universe as it comprises 85 percent of all mass found in it and is suspected to have caused the growth of galaxies.

In a new study to be presented at the Royal Astronomical Society’s National Astronomy Meeting, scientists from that country’s Durham University have found a possible explanation for why some dark matter didn’t form galaxies in the early Universe – gas that would have created galaxy was sterilized by the heat from the first stars that formed in the Universe.

“I’ve been losing sleep over this for the last 30 years,” said Carlos Frenk, Director of Durham University’s Institute for Computational Cosmology. “Dark matter is the key to everything we know about galaxies, but we still don’t know its exact nature. Understanding how galaxies formed holds the key to the dark matter mystery.”

According to theory, dark matter in the early Universe trapped interstellar gas in ‘halos’ that would eventually become galactic nurseries. However, some of these halos never lit up with new galaxies. The researchers pointed to our own ‘local’ neighborhood in the Universe and said there should be more galaxies near the Milky Way, based on this theory.

Using highly complex computer simulations, the study team was able to determine that heat from a first few initial stars ruined the possibility of other stars forming. Perhaps as a nod to the ongoing FIFA World Cup, the study researchers described this as a sort of “cosmic own goal.”

“We have learned that most dark matter halos are quite different from the ‘chosen few’ that are lit up by starlight,” Frenk said. “Thanks to our simulations we know that if our theories of dark matter are correct then the Universe around us should be full of halos that failed to make a galaxy. Perhaps astronomers will one day figure out a way to find them.”

“What we’ve seen in our simulations is a cosmic own goal,” said Till Sawala, an astrophysicist at Durham. “We already knew that the first generation of stars emitted intense radiation, heating intergalactic gas to temperatures hotter than the surface of the sun. After that, the gas is so hot that further star formation gets a lot more difficult, leaving halos with little chance to form galaxies.”

“We were able to show that the cosmic heating was not simply a lottery with a few lucky winners,” Sawala added. “Instead, it was a rigorous selection process and only halos that grew fast enough were fit for galaxy formation.”

In addition to shedding some new light on dark matter, the new study is also the first to simulate the evolution of our own ‘Local Group’ of galaxies, which includes the popular Andromeda Galaxy. These simulations are a part of Durham University’s larger EAGLE project, which will attempt to simulate from the beginning the formation of galaxies in a representative volume of the Universe.