Astronomers discover inexplicably massive "dark" star clusters
Astronomers havediscovered a series of unusual globular star clusters with masses farexceeding what would be expected under the standard model for thecelestial structures. The clusters are located in the giantelliptical galaxy Centaurus A, and seem to hint at an enigmatic darkpresence that cannot yet be accounted for.
A globular cluster isessentially an enormous spherical collection of thousands of starsthat orbit like satellites around large galaxies. It is believed thatCentaurus A may play host to as many as 2,000 clusters, a significantamount of which exhibit the same strange, massive characteristics.
Astronomers were ableto estimate the mass of a sample of 125 of the globular clustersusing the FLAMES instrument mounted on the ESO's Very Large Telescopeat the Paranal Observatory in Chile. The masses were then compared tothe luminosity of the clusters, from which the team were then able todeduce the rough number of stars contained in the sphericalstructures. It was discovered that the mass of the clusters farexceeded the estimated number of stars.
In terms of appearance,the newly-discovered clusters bear no distinction to the 150 ordinaryspecimens orbiting the Milky Way. However, the strange readings hintat a mysterious, as yet unaccounted for, celestial presence.
Possible explanationsfor the unexpected mass include the presence of black holes, acollection of stellar remnants at the core of the clusters, or even aconcentration of dark matter. The latter option, while enticing,seems unlikely, as globular clusters are generally considered to besingularly lacking of the enigmatic material.
"We have stumbled on a newand mysterious class of star cluster!" states PhD student Matt Taylor of the Pontificia Universidad Catolica de Chile, Santiago, Chile, and lead author of a paper on the study. "This shows that we still havemuch to learn about all aspects of globular cluster formation. It’san important result and we now need to find further examples of darkclusters around other galaxies."
Astronomers will continue to search for further examples of the new class of dark cluster.