Astronomers Discover Why Ancient Disk Galaxies All Look Alike

Disk galaxies are known for their smooth looks and predictable appearance. In fact, all of these galaxies eventually grow out of their irregular, clumped appearance and their older stars fade from a bright center to a dim edge. Now, astronomers have discovered exactly why these galaxies all take on the same "look" over time.

In order to find out exactly why disk galaxies all look the same, the researchers employed a computer model that simulated galaxy evolution. This model included a razor-thin disk and orbiting stars subject to the gravity of the massive clumps. Although the scientists thought that the clumpy structure of young galaxy disks might be responsible for both its own erasure and the smooth universal brightness profile, it turned out that this wasn't the case.

The scientists found that the gravity of clumps of interstellar gases and new stars alter the orbits of nearby stars. In some cases, these changes are significant; they can scatter stars well away from their original and nearly circular orbits. Over time, this scattering produces the smooth fade in brightness from the center of a galaxy to its edge.

"This process takes a few hundred million years to a few billion years," said Curtis Struck, one of the researchers, in a news release.

In fact, the findings actually match the data currently coming from the Hubble Space Telescope and large ground-based telescopes. Even so, more work still needs to be done in order to explain the smooth, steady fade of older disk galaxies. The scientists plan to add additional complexities to their models in order to see whether or not these factors can explain these features.

That said, the current models have provided a good explanation for the universal appearance of older disk galaxies. It turns out that, in fact, the forces of the galaxies eventually change them so that they all look alike.

"If there is some disturbance, some clumpiness in the galaxy, you eventually get this smooth profile," said Struck.

The findings are published in The Astrophysical Journal.