Starship Asterisk*

This illustration shows how two sample star orbits are scattered from nearly circular orbits by the gravity of massive clumps within galaxies. Researchers have found that millions of orbital changes, like those shown here, smooth the overall light profile of galaxy disks. The blue star is scattered several times. The orange star is captured by the gravity of a clump and moves around it. A typical, relatively smooth spiral galaxy (UGC 12224) is shown in the background. Illustration: Jian Wu. Galaxy Image: SDSS

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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 ... 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. ...

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. ...

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. ...

• Monthly Notices of the RAS (online 15 Sep 2020) DOI: 10.1093/mnras/staa2750
• arXiv.org > astro-ph > arXiv:2009.01929 > 03 Sep 2020