Globular Clusters Evolve in Interesting Ways Over Time

Globular clusters are among the oldest objects in the Universe. The early Universe was filled with dwarf galaxies and its just possible that globular clusters are the remains of these ancient relics. Analysis of the stars in the clusters reveals ages in the region of 12-13 billion years old. A new paper just published shows that the globular clusters are home to two distinct types of stars; the primordial ones with normal chemical composition and those with unusual heavy amounts of heavier elements. 

Globular clusters are dense, spherical collections of stars that orbit the outer regions of galaxies, usually in the galactic halo. They contain hundreds of thousands, sometimes millions of stars bound together by gravity. They differ from open clusters, which are younger and less tightly bound and found in the main body of a galaxy. Globular clusters in contrast, are ancient with ages typically in the regions of 10 to 13 billion years old. 

M13 – Credit: R. Jay GaBany

There stellar components are mostly composed of low-mass, metal-poor stars, suggesting they formed early in the history of the universe before the heavier elements appeared. Studying globular clusters can reveal lots about stellar evolution, the formation of galaxies and even dark matter. Our own Galaxy the Milky Way is home to over 150 known globular clusters like well known M13 in the northern hemisphere or Omega Centauri in the southern hemisphere.

Omega Centauri is the brightest globular cluster in the night sky. It holds about 10 million stars and is the most massive globular cluster in the Milky Way. It’s possible that globulars and nuclear star clusters are related in some way as a galaxy evolves. Image Credit: ESO.

In a paper recently published in Astronomy and Astrophysics, a team of researchers have advanced our understanding of these clusters by revealing more about their formation and dynamical evolution. The team led by Emanuele Dalessandro from the National Institute for Astrophysics (INAF) explored multiple populations of stars in the clusters. They studied the change in positions of the stars and their velocity in the first 3D kinematic analysis of 16 globular clusters. 

The team used data from ESA’s Gaia telescope the European Southern Observatory Very Large Telescope and Multi Instrument Kinematic Survey to measure the 3D velocity of stars within the clusters. This was a combination of proper motion (motion across the sky) and radial velocity (motion towards and away from us.) To gather the measurements, spectroscopic survey data was used.

Artist’s impression of the Gaia spacecraft detecting artificial signals from a distant star system. In this synchronization scheme, the star system’s inhabitants send the signal shortly after witnessing a supernova, which is also seen by telescopes on Earth. (Credit: Danielle Futselaar / Breakthrough Listen)

The formation and evolution of globular clusters has been one of the most hotly debated questions for the last few decades. The significance of understanding them is huge explains Dalessandro,’because they not only help us to test cosmological models of the formation of the Universe due to their age but also provide natural laboratories for studying the formation, evolution, and chemical enrichment of galaxies.’ Understanding the physical processes behind their formation was key to understanding how they evolve. This was the goal of their study which revealed for the first time that globular cluster form through multiple star formation events. 

Source : The first 3D view of the formation and evolution of globular clusters

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