Hidden dark matter found in nearby star clusters

A new study of neighboring galaxy Centaurs A suggests that it might be hiding dark matter.
By Tyler Henderson | May 15, 2015
ESO's Very Large Telescope in Chile has identified a new class of dark globular star clusters around the galaxy Centaurus A. The mysterious clusters resemble normal ones, but have a much higher mass. This suggests that the cluster is home to either large amounts of dark matter or massive black holes, and astronomers aren't sure which.

Globular star clusters are traveling balls of stars that orbit most known galaxies. They are among the oldest star clusters in the universe, having survived the turbulent period of early galactic formation and evolution.

Matt Taylor of the Pontificia Universidad Catolica de Chile in Santiago, the study's lead author, said that globular clusters and the stars they orbit are the keys to understanding how galaxies were formed. Conventional wisdom held that the stars in globular clusters were more or less uniform, but recent research suggests they are much more complicated.

The closest giant galaxy to the Milky Way is the elliptical giant Centaurus A, formally known as NGC 5128. Up to 2000 globular clusters are thought to orbit Centaurus A, many of which are brighter and more massive than those circling the Milky Way.

Taylor's work involved surveying the mass of a sample of clusters around Centaurus A, and his findings surprised the entire astronomy community. Typically, brightness correlates positively with mass. The lighter a cluster, the heavier you would expect it to be. Galaxies observed in the sample, however, were way heavier than they appeared to be. There must have been an explanation for the invisible mass.

There are a number of theories about the heavy globular clusters. It's possible that they contain black holes, or other hidden masses that don't give off much energy. Though not common, Taylor suggests that dark matter could account for the extra mass in the clusters. Whatever the theory, researchers will be pointing their lens back towards Centaurs A to find out soon.

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