A study done by researchers from The University of Hong Kong Department of Physics led by Dr. Jeremy Lim and his Research Assistant Miss Emily Wong has shown a surprising answer to the origin of some globular clusters—these are the collections of stars that have been seen around giant galaxies at the centers of galaxy clusters. With the utilization of data from the Hubble Space Telescope, the study was done in collaboration with Professor Thomas Broadhurst at the Ikerbasque in Spain and a professor at the HKU Department of Physics, Dr. Youichi Ohyama at the Academia Sinica Institute of Astronomy and Astrophysics in Taiwan and Dr. Elinor Medizinski at Princeton University in America. This report was published in the journal paper "Sustained Formation of Progenitor Globular Clusters in a Giant Elliptical Galaxy," as seen in the website Nature Astronomy.
What are globular clusters
Globular clusters are the oldest visible objects that are seen in the Universe. They contain millions of stars that are all born at essentially the same time, and they are packed into a spherical volume. Globular clusters have formed soon after the Universe began, which is roughly 13 billion years ago, or even more. They have remained largely unchanged, aside from the aging and the death of their constituent stars.
Dr. Lim's research team found out through the study that globular clusters around the giant galaxy that is located at the center of the Perseus galaxy cluster are not all ancient objects. Around a few thousand of them have formed over at least the past 1 billion years. The new globular clusters are linked in a complex filamentary network of cool gas that extends to the outer reaches of the giant galaxy.
The cool gas is thought to have precipitated from the hot gas that infuses the whole Perseus galaxy cluster, the density of the hot gas, and the rate at which this gas cools increased fast towards the center of the galaxy cluster. Once they form, the small globular clusters are no longer tied to the network of Acool gas and rain inwards onto the giant galaxy. It is similar to how raindrops condense and fall from clouds. By contrast, the older globular clusters are distributed at random around the giant galaxy, owing to random scatterings of each other during their orbits around the giant galaxy.
How this discovery answered questions about the galaxy
This amazing discovery by Dr. Lim and his team explains a lot of puzzling aspects about globular clusters around giant galaxies. Their numbers are now clear, as some fraction of globular clusters around the giant galaxies formed through cosmic history from the gas that infuses galaxy clusters. The broad range of colors was also included in the study, as it was exhibited by globular clusters around giant galaxies, the colors of globular clusters change progressively from blue to red as they age.
The globular clusters were located at the center of the Perseus galaxy, but since the number of globular clusters depend on the level of mass in the galaxy, it diminishes at areas with high masses. The number dependence of globular clusters with mass follows the same trend as the ancient globular clusters, as well as less massive star clusters in our galaxy and other spiral galaxies. This proves that the common formation mechanism for star clusters is the mass scales, regardless of the environment in which they are formed.
