Astronomers model, determine how disk galaxies evolve so smoothly

September 25, 2020

AMES, Iowa - 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.

Stars are scattered, disks are smoothed

The latest computer modeling - led by Wu - is a capstone topping years of model improvements, Struck said. Previous models treated the gravitational forces of galaxy components more approximately, and researchers studied fewer cases.

The latest models show how star clusters and clumps of interstellar gases within galaxies can change the orbits of nearby stars. Some star-scattering events significantly change star orbits, even catching some stars in loops around massive clumps before they can escape to the general flow of a galaxy disk. Many other scattering events are less powerful, with fewer stars scattered and orbits remaining more circular.

"The nature of the scattering is far more complex than we previously understood," Struck said. "Despite all this complexity on small scales, it still averages out to the smooth light distribution on large scales."

The models also say something about the time it takes for these exponential galaxy disks to form, according to the researchers' paper. The types of clumps and initial densities of the disks affect the speed of the evolution, but not the final smoothness in brightness.

Speed in this case is a relative term because the timescales for these processes are billions of years.

Over all those years, and even with model galaxies where stars are initially distributed in a variety of ways, Wu said the models show the ubiquity of the star-scattering-to-exponential-falloff process.

"Stellar scattering is very general and universal," he said. "It works to explain the formation of exponential disks in so many cases."
-end-


Iowa State University

Related Astronomy Articles from Brightsurf:

Spitzer space telescope legacy chronicled in Nature Astronomy
A national team of scientists Thursday published in the journal Nature Astronomy two papers that provide an inventory of the major discoveries made possible thanks to Spitzer and offer guidance on where the next generation of explorers should point the James Webb Space Telescope (JWST) when it launches in October 2021.

New technology is a 'science multiplier' for astronomy
A new study has tracked the long-term impact of early seed funding obtained from the National Science Foundation on many key advances in astronomy over the past three decades.

Powerful new AI technique detects and classifies galaxies in astronomy image data
Researchers at UC Santa Cruz have developed a powerful new computer program called Morpheus that can analyze astronomical image data pixel by pixel to identify and classify all of the galaxies and stars in large data sets from astronomy surveys.

Astronomy student discovers 17 new planets, including Earth-sized world
University of British Columbia astronomy student Michelle Kunimoto has discovered 17 new planets, including a potentially habitable, Earth-sized world, by combing through data gathered by NASA's Kepler mission.

Task force recommends changes to increase African-American physics and astronomy students
Due to long-term and systemic issues leading to the consistent exclusion of African-Americans in physics and astronomy, a task force is recommending sweeping changes and calling for awareness into the number and experiences of African-American students studying the fields.

How to observe a 'black hole symphony' using gravitational wave astronomy
New research led by Vanderbilt astrophysicist Karan Jani presents a compelling roadmap for capturing intermediate-mass black hole activity.

Graphene sets the stage for the next generation of THz astronomy detectors
Researchers from Chalmers University of Technology have demonstrated a detector made from graphene that could revolutionize the sensors used in next-generation space telescopes.

3D holograms bringing astronomy to life
Scientists unravelling the mysteries of star cluster formation have taken inspiration from a 19th century magic trick, to help explain their work to the public.

The vibrating universe: Making astronomy accessible to the deaf
Astronomers at the University of California, Riverside, have teamed with teachers at the California School for the Deaf, Riverside, or CSDR, to design an astronomy workshop for students with hearing loss that can be easily used in classrooms, museums, fairs, and other public events.

Prehistoric cave art reveals ancient use of complex astronomy
As far back as 40,000 years ago, humans kept track of time using relatively sophisticated knowledge of the stars

Read More: Astronomy News and Astronomy Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.