An international team of researchers at the Paranal Observatory in northern Chile have used ESO’ Very Large Telescope to discover a kind of star clusters which was never met before around the huge galaxy NGC 5128, also known as Centaurus A. The study was published in the Astrophysical Journal.
Centaurus A is a big elliptical galaxy lying 12 million light years away from our Milky Way galaxy which makes it the closest galaxy to ours. Astronomers analyzed the globular star clusters that floated around it. The lead author of the study, PhD student Matt Taylor from the Pontificia Universidad Catolica de Chile (Santiago), explained that global clusters which are united collections of stars that orbit galaxies together with their constituents the essential factor to understanding how galaxies have formed and evolved. He also added that astronomers have believed for decades that the stars which compose a certain globular cluster must all share the same chemical composition and the same ages, but this new study proves that things are more complicated than that.
For their research the investigators have conducted the most detailed research of a sample of 125 globular star clusters from around the Centaurus A galaxy. Their observations helped them estimate the mass of the clusters and compared it with the brightness of the clusters.
Co-author of the study, Thomas Puzia, also from the Pontificia Universidad colleague, explained they discovered that the start clusters have an unexpected high mass for the amount of starts which they contain. This fact indicates that global clusters can be found as multiple families which have different formation histories. He also remarked:
”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.”
Some of the globulars have strange features: they are much more massive than they look. In addition the more massive they were the darker was the fraction of their material. In some cases there was something dark and massive hidden in the clusters. These newly discovered objects were named dark globular star clusters. Scientists suspect that they could either harbor unbelievable amounts of dark matter or carry massive black holes. Neither of these alternatives was understood or expected.
Taylor described this new class of star cluster as being mysterious which indicates that astronomers still have much to learn about the formation of globular clusters. He added that further examples of such dark clusters should be investigated.
Image Source: Science World Report