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Globular Cluster. Globular clusters are stable, tightly bound clusters of tens of thousands to millions of stars. They are associated with all types of galaxies. Photo credit: NASA, ESA

Researching 1 billion years of cosmic history with IU's Big Red 200 supercomputer

Dr. Francesco Calura, an IU collaborator from the Astrophysics and Space Science Observatory of Bologna (OAS) uses Big Red 200 to model the formation of globular clusters.

Francesco Calura is attempting to model the formation of globular clusters in a cosmological context using IU's newest supercomputer, Big Red 200. Dr. Calura is a researcher for the Astrophysics and Space Science Observatory of Bologna (OAS): the latest branch of the Italian National Institute for Astrophysics (INAF). He collaborates with Enrico Vesperini, faculty for the IU Department of Astronomy. Surprisingly, Dr. Calura found that Big Red 200 had the capability to research approximately 1 billion years of cosmic history using a set of simulations with unique features, such as tremendously high resolution, taking into account the presence of single stars and how they affect the system, and how much energy and mass each of them restores.

Dr. Francesco Calura from the Astrophysics and Space Science Observatory of Bologna (OAS) and a collaborator with IU faculty.

[Big Red 200's] performance is amazing and unprecedented.

Dr. Francesco Calura

Globular clusters (GCs) are stable, tightly bound systems of tens of thousands to millions of stars. The intense gravitational attraction between the closely packed stars gives globular clusters their regular, spherical shape. One might wonder why astronomers are so interested in globular clusters. Dr. Calura explains, "Our ignorance regarding the physical processes in these systems is huge." Consequently, star clusters are of great interest to astronomers because their constituent stars all formed at approximately the same time and location and had a similar composition. Therefore, stellar clusters offer unique insights into how stars form and evolve.

This cluster of stars is known as Messier 15, and is located some 35,000 light-years away in the constellation of Pegasus (The Winged Horse). It is one of the oldest globular clusters known, with an age of around 12 billion years.

Photo credit: NASA, ESA

Dr. Calura's research will offer a unique look into this mystery of how stars form and evolve in stellar aggregates at early times. According to Dr. Calura, "Being able to model, using cosmological sub-parsec resolution simulations, the past evolution of a unique, star-forming complex detected at redshift z=6.14, will be convenient and timely." This star-forming complex will soon be the target of a James Webb Space Telescope observational program, and having predictions regarding the structure of this system before the observations begin will be advantageous.

According to the James Webb Space Telescope's FAQs, the James Webb Space Telescope, also called Webb or JWST, is a large, space-based observatory optimized for infrared wavelengths, complementing and extending the discoveries of the Hubble Space Telescope. It will have longer wavelength coverage and greatly improved sensitivity. The longer wavelengths enable Webb to look further back in time to find the first galaxies that formed in the early Universe and to peer inside dust clouds where stars and planetary systems are forming today.

Image of a gas density map at 0.83 billion years of cosmic time, created from one of Dr. Calura’s cosmological simulations. It shows the progressive collapse of the cosmic structures within the computational box. The map shows how gas collapses and, through the filaments, is collected in bound structures, represented by the overdense light knots, which grow in density and number as cosmic time goes by. The physical scale is on the bottom left.

Generally, researchers model stars in the form of macroscopic particles, which represent groups of stars or single star clusters, not individual stars. Dr. Calura will be able to account for the presence and physical processes of individual stars within a globular cluster in a cosmological simulation. This is one of the first times to attempt such an ambitious numerical experiment.

When Dr. Calura first started this research project, he tried running simulations on other IU machines, namely Quartz and Big Red 3, and he was essentially stuck. Upon moving his project to Big Red 200, IU's newest and fastest supercomputer, he was able to run a hugely memory-intensive job on only ten nodes. According to Dr. Calura, "[Big Red 200's] performance is amazing and unprecedented." Dr. Calura is one of the first researchers ever to attempt this type of research in a fully cosmological context with a grid code like he is using.

This is just the beginning of Dr. Calura's research. This research is a significant step towards a more physical description of the modeled system. This research establishes the solid ground for a series of studies that will bring considerable progress in understanding faint systems and their sub-components in early cosmic epochs.