How Galaxies Feed: Cosmic Swirly Straws Suck up Funnels of Fuel

Galaxies form over billions of years, using cosmic material to form planetary bodies. Now, researchers have discovered how these galaxies actually feed; they may employ a cosmic version of swirly straws.

In the early universe, galaxies formed out of clumps of matter connected by filaments in a giant cosmic web. Within these galaxies, nuggets of gas cooled and condensed. This gas eventually became dense enough to trigger the birth of bright stars. In fact, our own Milky Way spiral galaxy and its billions of stars took shape in this way.

There have been many theories about how exactly galaxies form. In a previous theory, researchers believed that hot gas sank into the centers of burgeoning galaxies from all directions. Gas clouds collided into each other, sending out shock waves that heated up the gas. Eventually, the gas cooled and sank to the galactic center, taking as much as eight billion years to complete. Yet this particular theory was contradicted in smaller galaxies where the gas was not heated.

In order to test the two theories, the researchers created computer models to watch how a galaxy grows. They ran four different simulations of the formation of a galaxy like our Milky Way. They started from just 57 million years after the Big Bang until the present day.

"The simulations are like a gigantic game of chess," said Alyson Brooks, co-author of the paper and expert in galaxy simulations, in a news release. "For each point in time, we had to figure out how a given particle--our chess piece--should move based on the positions of all of the other particles. There are tens of millions of particles in the simulation, so figuring out how the gravitational forces affect each particle is time-consuming."

So what did they find? The researchers discovered that the models confirmed that cold gas--fuel for stars--spirals along filaments into the cores of galaxies. This gas rapidly makes its way into the galaxy's "guts" where it is converted into new stars. In addition, they show for the first time that the gas is spinning around faster than previously believed. The simulations also revealed that the gas is making its way down to the centers of galaxies more quickly than what occurs in the "hot-mode" of galaxy formation--it only takes about one billion years.

The findings help answer a few questions about the formation of galaxies--especially those with large, extended disks of material spinning around them, far from their centers. The research could allow scientists to further understand other questions about our universe, and could be built upon in future studies.

"The goal of simulating galaxies is to compare them to what telescopes observe and see if we really understand how to build a galaxy," said Kyle Stewart, lead author, in a news release. "It helps us make sense of the real universe."

The findings are published in The Astrophysical Journal.

Want to see the galaxy form for youself? Check out the video below, courtesy of NASA.