28May2013

Swirling Into A Galaxy

Image Credit: JPL/NASA

Image Credit: JPL/NASA

Did you every play with a Silly Straw when you were a kid? Even as an adult, it’s quite fun to watch as your drink is pulled away from its source and into you. Strangely there’s science there.

Now astronomer have used computer simulations to show how some galaxies have grown in a similar scenario… a regular “cosmic version of the swirly straw!” The study has revealed that cold gas, the progenitor of stars, is pulled into the nucleus of galaxies along filaments and into their structure. Once it has been ingested into the galaxy, the gas then becomes the fuel for stellar creation and the galaxies take on mass.

“Galaxy formation is really chaotic,” said Kyle Stewart, lead author of the new study appearing in the May 20th issue of the Astrophysical Journal. “It took us several hundred computer processors, over months of time, to simulate and learn more about how this process works.” Stewart, who is now at the California Baptist University in Riverside, California, completed the majority of this work while at NASA’s Jet Propulsion Laboratory in Pasadena, California.

When the Universe was young, galaxies formed from huge globs of matter and were connected by filaments like a “giant cosmic web”. Inside the galaxies, smaller pockets of matter then cooled and condensed – the essence of star formation. It’s a process that’s common to galaxy formation and shared by our own Milky Way galaxy. Previous studies of galaxy formation told us the hot gas sank to the center from all directions – possibly interacting with each other. This may have caused shock waves which, in turn, heated the gas. It’s all a very slow process, once which could take up to 8 billion years to happen.

The new research gives us fresh insight, especially when it comes to smaller galaxies. It theorizes that the gas isn’t heated. Instead it has an alternate “cold mode” – once which allows the material to be pulled along the filaments and into the galactic core. Stewart and his colleagues set out to test this theory and address the mysteries about how the cold gas gets into galaxies, as well as the rate at which it spirals in.

Because it would require billions of years to actually observe this function, the team simulated the process using supercomputers at JPL; NASA’s Ames Research Center, Moffett Field, California; and the University of California, Irvine. Their studies included four varied simulations of galaxy formation, starting about 57 million years after the Big Bang and up to the present. These simulations begin with galactic raw ingredients like hydrogen, helium and dark matter. From there it’s just a matter of following the laws of physics.

Embedded video from : NASA Jet Propulsion Laboratory California Institute of Technology

“The simulations are like a gigantic game of chess,” said Alyson Brooks, a co-author of the paper and expert in galaxy simulations at 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.”

Once the simulations were complete, the researchers reviewed the data looking for new information about how cold gas penetrates galactic centers. Their results confirm that cold gas flows along the filaments. For the first time the gas is shown spiraling downward much faster than once thought. These simulations have also shown it is moving far faster than expected.

“We have found that the filamentary structures that galaxies are built on are key to how they build up over time, by threading gas into them efficiently,” said Leonidas Moustakas, a co-author at JPL.

But that’s not all. The researchers have also investigated dark matter – the enigmatic structure which accounts for about 85% of the Universe. Since galaxies form from regular matter – the so-called baryonic matter that is composed of atoms, and dark matter, scientists were curious about its spin rate. What they revealed is dark matter is also swirling along the filaments at a faster rate and dropping into the forming galactic cores.

These new insights are helping astronomers understand why some galaxies with extended disks of material spinning around them have such a distance from their cores. By examining the “code mode”, the answer appears to be in sync with computer simulations..

“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 Stewart. “It helps us makes sense of the real Universe.”

Original Story Source: JPL/NASA News Release. Submitted by Tammy Plotner for “Dave Reneke’s World of Space and Astronomy News”.

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