The Genesis of Galaxy Eris…

by Tammy Plotner on September 1, 2011

This image of the Eris simulation shows the stars in the galaxy as observers would see it. Blue colors are regions of recent star formation, while redder regions are associated with older stars. The spiral arms are typically star-forming, and the central bulge is basically "red and dead." Credit: J. Guedes and P. Madau.

In as much time as it takes to give birth to human life, a supercomputer and a team of researchers at the University of California, Santa Cruz, and the Institute for Theoretical Physics in Zurich have given rise to the first simulation of the physics involved in galaxy formation that produced the Milky Way. They named their child Eris…

“Previous efforts to form a massive disk galaxy like the Milky Way had failed, because the simulated galaxies ended up with huge central bulges compared to the size of the disk,” said Javiera Guedes, who recently earned her Ph.D. in astronomy and astrophysics at UC Santa Cruz and is first author of a paper which has been accepted for publication in the Astrophysical Journal.

This comparison shows the Eris simulation (top) and the Milky Way (bottom). Credit: S. Callegari, J. Guedes, and the 2MASS collaboration.

Like the Milky Way, Eris is a lovely barred spiral galaxy – her figure and star content as identical as modeling can make it. By studying our own galaxy and others like it, this simulation fits the mold from every angle. “We dissected the galaxy in many different ways to confirm that it fits with observations,” Guedes said.

And “seven sisters” were involved in the project, too. NASA’s state-of-the-art Pleiades supercomputer took on the task of 1.4 million processor-hours. But the calculations didn’t stop there. Simulations on supercomputers at UCSC and the Swiss National Supercomputing Center were involved, too. “We took some risk spending a huge amount of supercomputer time to simulate a single galaxy with extra-high resolution,” Madau said.

For over two decades, attempts at creating the evolution of a Milky Way type galaxy have been just outside the grasp of researchers. They just weren’t able to produce the proper shape, size and population to fit known properties. Thanks to this new breakthrough, support for the “cold dark matter” theory has predominated and the Big Bang theory supported. What gave Eris the edge? Try our now better understanding star formation.

“Star formation in real galaxies occurs in a clustered fashion, and to reproduce that out of a cosmological simulation is hard,” Madau said. “This is the first simulation that is able to resolve the high-density clouds of gas where star formation occurs, and the result is a Milky Way type of galaxy with a small bulge and a big disk. It shows that the cold dark matter scenario, where dark matter provides the scaffolding for galaxy formation, is able to generate realistic disk-dominated galaxies.”

Giving birth to Eris wasn’t an easy task. Through low-resolution simulations, researchers began assembling clumps of dark matter – shaping them into galactic halos. From there they selected information on a halo with similar mass and merger history to our own and “rewound the tape” to its infancy. By focusing on a small area, they were able to add additional particle information and step up the resolution.

“The simulation follows the interactions of more than 60 million particles of dark matter and gas. A lot of physics goes into the code–gravity and hydrodynamics, star formation and supernova explosions–and this is the highest resolution cosmological simulation ever done this way,” said Guedes, who is currently a postdoctoral researcher at the Swiss Federal Institute of Technology in Zurich (ETH Zurich).

What sets Eris apart from its predecessors is the ability to “see” in high resolution / high density. This allows for a more pragmatic approach to star formation and placement. It’s an important consideration, because supernova occur in high density regions and high resolution allows them to be taken into account.

“Supernovae produce outflows of gas from the inner part of the galaxy where it would otherwise form more stars and make a large bulge,” Madau said. “Clustered star formation and energy injection from supernovae are making the difference in this simulation.”

Arise, Eris… Your time has come!

Original Story Source: University of Santa Cruz News. For Further Reading: Forming Realistic Late-Type Spirals in a LCDM Universe: The Eris Simulation.

About 

Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.

Comments on this entry are closed.

Previous post:

Next post: