How Galaxy Star Formation is Powered by the Cosmic Web

How do galaxies form and how do they evolve? How are they impacted by their surrounding environment? These are both good questions and now, astronomers have taken a closer look at the "cosmic web" of our universe in order to propose some answers.

The cosmic web is a large-scale, web-like structure composed of galaxies that stretches across our universe. It played a role in the evolution of galaxies at the beginning of our universe, a few billion years after the Big Bang. In fact, scientists believe that "filaments" in this cosmic web played an especially important role in galaxy evolution.

"We think the cosmic web, dominated by dark matter, formed very early in the history of the universe, starting with small initial fluctuations in the primordial universe," said Behnam Darvish, one of the researchers, in a news release. "Such a 'skeletal' universe must have played, in principle, a role in galaxy formation and evolution, but this was incredibly hard to study and understand until recently."

Galaxies are organized in an enormous network, the cosmic web. This web has dense regions made up of galaxy clusters and groups, and sparsely populated regions devoid of galaxies in addition to the filaments linking these regions together. Think of a spider web with water droplets clinging to the strands. The droplets represent the dense regions while the strands of the web represent the less-dense regions and filaments.

In order to better study the cosmic web in the early universe, the scientists used data from two large cosmological surveys, COSMOS and HiZELS. Then, the scientists applied a new computation method to identify the filaments of the web which, in turn, allowed them to study the web itself.

The researchers found that galaxies residing in the cosmic web and filaments have a much higher chance of actively forming stars. In other words, it seems that in the distant universe, galaxy evolution was accelerated in the filaments.

"We were surprised by the crucial role the filaments play in galaxy formation and evolution," said Bahram Mobasher, one of the researchers. "Star formation is enhanced in them. The filaments likely increase the chance of gravitational interaction between galaxies which, in turn, results in this star-formation enhancement. There is evidence in our local universe that this process in filaments also continues to occur at the present time."

The findings are published in The Astrophysical Journal.