Russian scientists have researched nuclear globular clusters (NGCs) in two dwarf spheroidal galaxies (dSphs).
The results were published in Monthly Notices of the Royal Astronomical Society in 2017.
Studies of globular clusters, which are some of the oldest structures in the Universe, help understand the general evolution of stars and galaxies. It is theorized that such clusters emerged from the same relic matter with galaxies. Stars in globular clusters include very small amounts of heavy elements in comparison with Sun. This means that they are much older than our star or similar objects.
Associate Professor Vladislav Shimansky, one of the participants of the project group and the main designer of “Cluster” software, explains, “While researching these massive globular systems with hundreds of thousands of stars, we can peek into the earliest stages of galaxy formation and find out about their chemical and physical properties at that time.
“The idea to analyze spectra of star clusters was first put forth 15 years ago by Margarita Sharina, KFU alumna, now Senior Research Associate of the Special Astrophysical Observatory. Usually, globular clusters are million light years away from the Earth, so it’s practically impossible to observe separate stars in them. However, total luminosity of such clusters is much higher than of individual stars, so we can analyze them in the same way in which we analyze individual stars of the Milky Way. As a result, we have a thousand-fold increase in the volume of the Universe space where we can correctly determine physical characteristics of stars, their chemical composition and age.
“We have to build a mathematical model of a specific spectrum, determine the number of stars of different types, and calculate their spectra. Fortunately, characteristics of stars in such clusters are not chaotic; they fit into strict regularities predetermined by their evolution, age, and chemical composition. By calculating such regularities we can significantly ease our burden and limit ourselves with modelling only hundreds, and not hundreds of thousands, of spectra. Even this relatively smaller task seemed unapproachable because it required immense computing power and information about tens of millions of spectral lines which were unknown just 15 years ago.”
However, in 2010s many large telescopes have provided spectra of hundreds of extragalactic clusters, and physicists have been able to calculate atomic data.
Dr. Shimansky continues, “That’s why we decided to create this Cluster software to model spectra of clusters. At first, one calculation took several days, and we abandoned hope to use it for analysis. In these past years, though, Russian research centers have acquired computing equipment for multithread calculations, and Cluster became a comparatively available research instrument. As we found out later, German and British colleagues moved in the same direction and created such software a bit later.
“Our task was to determine fundamental characteristics of clusters in different galaxies. As it appears, they are identical in their dynamic properties (mass, radius, and speed dispersion) and chemical properties. We have shown that other galaxies have globular clusters similar to ours. This makes us rethink our theories of the emergence of such clusters which only weakly depend on the evolution of their galaxies. Clusters develop through several phases of star formation. We are now testing our takeaways by observing clusters in the Andromeda.”