Astronomers model, determine how disk galaxies evolve so smoothly — ScienceDaily

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Computer simulations are showing astrophysicists how massive clumps of gas within galaxies scatter some stars from their orbits, eventually creating the smooth, exponential fade in the brightness of many galaxy disks.

Researchers from Iowa State University, the University of Wisconsin-Madison and IBM Research have advanced studies they started nearly 10 years ago. They originally focused on how massive clumps in young galaxies affect star orbits and create galaxy disks featuring bright centers fading to dark edges.

(As Curtis Struck, an Iowa State professor of physics and astronomy, wrote in a 2013 research summary: “In galaxy disks, the scars of a rough childhood, and adolescent blemishes, all smooth away with time.”)

Now, the group has co-authored a new paper that says their ideas about the formation of exponential disks apply to more than young galaxies. It’s also a process that is robust and universal in all kinds of galaxies. The exponential disks, after all, are common in spiral galaxies, dwarf elliptical galaxies and some irregular galaxies.

How can astrophysicists explain that?

By using realistic models to track star scattering within galaxies, “We feel we have a much deeper understanding of the physical processes that resolve this almost-50-year-old key problem,” Struck said.

Gravitational impulses from massive clumps alter the orbits of stars, the researchers found. As a result, the overall star distribution of the disk changes, and the exponential brightness profile is a reflection of that new stellar distribution.

The astrophysicists’ findings are reported in a paper just published online by the Monthly Notices of the Royal Astronomical Society. Co-authors are Struck; Jian Wu, an Iowa State doctoral student in physics and astronomy; Elena D’Onghia, an associate professor of astronomy at Wisconsin; and Bruce Elmegreen, a research scientist at IBM’s Thomas J. Watson Research Center in Yorktown Heights, New York.

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