May 26, 2013
New Study Sheds New Light On ‘Cold Mode’ Galaxy Formation
redOrbit Staff & Wire Reports - Your Universe Online
As galaxies grow over the course of billions of years, they apparently use the cosmic equivalent of bendy straws to feed on cold gas and gain mass, according to new research published in the May 20 edition of the Astrophysical Journal.The study is based on computer simulations conducted by Kyle Stewart, who is currently with California Baptist University in Riverside but completed most of the research while with NASA´s Jet Propulsion Laboratory (JPL) in Pasadena.
Stewart´s simulations suggested that cold gas, which serves as fuel for stars, spirals into the cores of galaxies along filaments, the US space agency said in a statement. It rapidly moves towards the so-called “guts” of the galaxies and is converted into new stars upon its arrival, adding mass to the galaxies.
“Galaxy formation is really chaotic. It took us several hundred computer processors, over months of time, to simulate and learn more about how this process works,” Stewart explained. “The goal of simulating galaxies is to compare them to what telescopes observe and see if we really understand how to build a galaxy. It helps us makes sense of the real universe.”
Galaxies formed out of clumps of matter connected by filaments in the early universe, and within those galaxies, smaller nuggets of gas cooled and condensed. Once that happened, they became dense enough to spur forth the formation of stars, helping the Milky Way spiral galaxy and its billions of stars to take shape.
“The previous, standard model of galaxy formation held that hot gas sank into the centers of burgeoning galaxies from all directions. Gas clouds were thought to collide into each other, sending out shock waves, which then heated up the gas,” JPL officials explained in a recent statement. “The process is similar to jets creating sonic booms, only in the case of galaxies, the in-falling gas travels faster than the speed of sound, piling up into waves. Eventually, the gas cools and sinks to the galactic center. This process was theorized to be slow, taking up to 8 billion years.”
However, more recent studies have contradicted those scenarios in smaller galaxies, as they have demonstrated that the gas is not heated during the formation process. An alternate theory of galaxy formation method arose, suggesting that cold gas could funnel along filaments into the galaxy centers. Stewart and his colleagues set out to test this so-called “cold mode” theory, as well as figure out how that cold gas actually gets into those galaxies.
It would take several billion years to actually watch a galaxy grow, so the researchers opted instead to simulate the process using supercomputers at JPL, the Ames Research Center, and the University of California, Irvine. Stewart and his associates conducted four-different simulations of the formation of a spiral galaxy like the Milky Way, beginning at 57 million years following the big bang and ending with present day.
They started their models with the essential building blocks of galaxies — hydrogen, helium and dark matter — and then allowed the supercomputers to process the enormous amount of interactions required to simulate how the laws of physics shape galaxies. After the galaxies were ready, the researchers inspected the information and found that cold gas flows along filaments.
They also demonstrated for the first time that the gas spins around faster than previously thought, making its way to the center of galaxies more quickly than it does during the “hot mode” of galaxy formation. Stewart´s team also analyzed dark matter, and found that the abundant invisible substance also spins at a faster rate among the filaments as it ultimately spirals into the center of the galaxies.
“The results help answer a riddle in astronomy about galaxies with large extended disks of material spinning around them, far from their centers,” JPL said. “Researchers didn't understand how the outer material could be spinning so fast. The cold-mode allows for this rapid spinning, fitting another jigsaw piece into the puzzle of how galaxies grow.”
“The simulations are like a gigantic game of chess,” added Alyson Brooks, co-author of the study and an expert in galaxy simulations from the University of Wisconsin, Madison. “For each point in time, we have 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.”