Tuesday, May 24, 2022

Astronomers found an unprecedented number of possible globular clusters

A new treasure trove of globular clusters holds clues about galaxy evolution.

Centaurus A is the fifth brightest galaxy in the sky, located 13 million light-years from Earth in the constellation Centaurus. The galaxy is also known as NGC 5128- featuring a relativistic jet spewing from a supermassive black hole at its center.

Centaurus A is too far away to allow astronomers to see individual stars, but star clusters can be identified and used as “fossil evidence” of the galaxy’s tumultuous evolution.

Recently, scientists at the University of Arizona Department of Astronomy and Steward Observatory yielded a treasure trove of previously unknown globular clusters in Centaurus A. Using a combination of ground and space-based telescopes; the team completed a survey that yielded a new catalog of 40,502 globular clusters (GC) candidates in the outer regions of the elliptical galaxy Centaurus A.

Scientists surveyed globular cluster candidates out to a projected radius of approximately 150 kiloparsecs, nearly half a million light-years from the galaxy’s center. They gathered the data from the following sources: the Panoramic Imaging Survey of Centaurus and Sculptor, or PISCeS; Gaia, a space observatory of the European Space Agency; and the NOAO Source Catalog, which combines publicly accessible images from telescopes in both hemispheres covering nearly the entire sky.

Hughes said“Centaurus A’s structure tells astronomers that it went through several major mergers with other galaxies, leading to its glob-like appearance with river-like regions that have many more stars than the surrounding areas. Providing the closest example of an elliptical galaxy, Centaurus A offers astronomers an opportunity to study up close a galaxy that is very unlike our own. The Milky Way and its closest neighbor, the Andromeda Galaxy, are spiral galaxies. With their familiar, pinwheel-like appearance, spiral galaxies may seem like the “typical” galaxy, but it turns out that their less orderly elliptical cousins outnumber them in the cosmos.”

“Centaurus A may look like an odd outlier, but that’s only because we can get close enough to see its nitty-gritty details. More likely than not, both elliptical and spiral galaxies like the Milky Way are messier than we realize as soon as we look a little bit deeper than just on the surface.”

“Globular clusters serve as evidence of processes that happened a long time ago.”

“For example, if you see a line of these globular clusters that all have similar metallicity (chemical composition) and move with similar radial velocity, we know they must have come from the same dwarf galaxy or some similar object that collided with Centaurus A and is now in the process of being assimilated.”

“We specifically looked for globular clusters far from the center of the galaxy because Centaurus A’s substructure hints at a large, undiscovered population of such clusters. Previous observations had found just under 600 clusters in the more central regions, but the outer regions of the galaxy had remained largely uncharted.”

“We looked farther out and discovered more than 100 new clusters already, and most likely there are more because we haven’t even finished processing the data. We can then use that data to reconstruct the architecture and movements in that galaxy and figure out its mass. From that, we can eventually subtract all its stars and see what’s left – that invisible mass must be its dark matter.”

Journal Reference:

  1. Allison K. Hughes et al. NGC 5128 Globular Cluster Candidates Out to 150 kpc: A Comprehensive Catalog from Gaia and Ground-based Data*. DOI: 10.3847/1538-4357/abf63c

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