ESO Telescope Reveals Strange, Dark Globular Clusters Around a Giant Galaxy

With the help of ESO's Very Large Telescope, scientists have discovered a new class of "dark" globular clusters around the giant galaxy Centaurus A. The findings reveal a bit more about some of the oldest known stellar systems in the universe.

"Globular clusters and their constituent stars are keys to understanding the formation and evolution of galaxies," said Matt Taylor, one of the researchers, in a news release. "For decades, astronomers thought that the stars that made up a given globular cluster all shared the same ages and chemical compositions-but we now know that they are stranger and more complicated creatures."

In this case, the researchers looked at the elliptical galaxy Centaurus A, which is the closest giant galaxy to the Milky Way. It's thought to house as many as 2,000 globular clusters, many of which are brighter and more massive than the 150 orbiting the Milky Way.

The scientists sampled 125 globular star clusters around Centaurus A and then conducted detailed studies on them. They deduced the masses of the clusters and compared the results with how brightly each of the clusters shone.

Surprisingly, they found that some of the globular clusters did something strange; they were many times more massive than they appeared in terms of brightness. In addition, the more massive these unusual clusters were, the greater the fraction of their material was dark.

So what is this dark material? It's possible that these dark clusters contain black holes or other dark stellar remnants in their cores. It's also possible that for some reason, these clusters have retained significant dark matter clumps in their cores.

"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 Thomas Puzia, one of the researchers. "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."

The findings are published in the Astrophysical Journal.

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