What's in this 'dark' globular star cluster?

Chuck Bednar for redOrbit.com – @BednarChuck

While conducting studies using the ESO’s Very Large Telescope in Chile, a team of astronomers recently discovered an unusual, overstuffed type of globular star clusters in orbit around the giant elliptical galaxy Centaurus A (NGC 5128) that may be packed with dark matter.

The Observatory refers to these objects as a new class of “dark” globular star clusters, and many are brighter and more massive than the approximately 150 clusters currently orbiting the Milky Way. The clusters may contain a tremendous amount of dark matter, as mentioned above, or they may have a massive black hole hidden in their midst, according to Space.com.

“Globular clusters and their constituent stars are keys to understanding the formation and evolution of galaxies,” explained lead author Matt Taylor, a Ph. D. student at the Pontificia Universidad Catolica de Chile whose work has been published by The Astrophysical Journal.

For decades, astronomers thought that the stars that made up a given globular cluster all shared the same ages and chemical compositions,” Taylor, who also holds an ESO Studentship, added. “But we now know that they are stranger and more complicated creatures.”

Discovery suggests there are multiple types of star clusters

He and his colleagues have conducted what is being called the most detailed analysis to date of a sample of 125 globular star clusters around Centaurus A. They used those observations to find out the mass of the clusters, then took that data and compared it to how brightly each one of them shines. Most of the brighter clusters had a greater amount of mass than was expected.

Generally, clusters that contain a greater amount of stars are brighter and have more mass, but in the case of some of the newly observed globulars, they were many times more massive than they appeared. In addition, some of these massive clusters had a higher percentage of dark material, indicating that they contained something large and unseen. Spooky!

The causes of this phenomenon remain a mystery, but there are several possibilities.The dark clusters could contain black holes or other stellar remnants, or they may contain dark matter (even though most globular clusters do not). The first possibility would explain the presence of some of the hidden mass, but the team said it would not tell the whole story, and the second explains the results but is contrary to conventional theory.

“Our discovery of star clusters with unexpectedly high masses for the amount of stars they contain hints that there might be multiple families of globular clusters, with differing formation histories,” said co-author Thomas Puzia, also from the Pontificia Universidad Catolica de Chile. “Apparently some star clusters look like, walk like, and smell like run-of-the-mill globulars, but there may quite literally be more to them than meets the eye.”

—–

Follow redOrbit on Twitter, Facebook, Google+, Instagram and Pinterest.

redOrbit.com
offers Science, Space, Technology, Health news, videos, images and
reference information. For the latest science news, space news,
technology news, health news visit redOrbit.com frequently. Learn
something new every day.”