Institute of Astronomy

Astronomers find remains of ancient globular cluster

Published on 05/01/2022 

An international team of researchers (including astrophysicists from the University of Cambridge) have discovered a the remains of a unique globular cluster which appears to be a relic from the very early Universe. 

The fossil cluster was discovered using the Gaia spacecraft (which was launched by the European Space Agency in 2015). The team used Gaia’s detailed map of over a billion stars, and applied a novel algorithm designed to identify groups of stars moving in concert. Using this method the team identified a stream of stars (which was dubbed ‘C-19’) in the outskirts of our Galaxy. In parallel, the Pristine survey (conducted at the Canada-France-Hawaii Telescope in Hawaii) studied C-19’s stars, and found that C-19’s stars contain a remarkably low fraction of heavy elements — a far lower amount than had ever been seen before.

Follow-up observations (conducted with the Gemini North Telescope in Hawaii, and the Gran Telescopio Canarias in La Palma) confirmed that the amount of heavy elements in C-19’s stars is as low as 0.04% compared to our Sun — well below any other known structure in the Universe.  The combined observations suggest that C-19 must be the ancient remains of a globular cluster, which is shedding its stars in its billion-year orbit around the Milky Way, leaving a “stellar stream” in its wake for astronomers to find. 

Studying the first stars in the Universe is one of the key goals of modern astronomy. One way to achieve this is to look back in time to the most distant galaxies, more than 10 billion years in the past. But it is also possible to look closer to home. By finding and studying the oldest structures in our own galaxy, astronomers can examine the results of early star-formation in our cosmic backyard. This approach is known as ‘Galactic Archeology’. 

Starting soon after the Big Bang, generations of stars enrich the surrounding gas with heavy elements. The later in the Universe stars form, the more heavy elements they contain. The minuscule fraction of these heavy elements within C-19 suggests that the cluster must have formed at the very earliest times. C-19 is a remarkable fossil relic, preserved from the period in the Universe’s distant past when the very first stellar structures were assembling. Before the discovery of C-19, globular clusters with such a low fraction of heavy elements were thought to be either extinct — or entirely impossible.

“This artefact from ancient times opens a direct and unique window into the early epochs of star formation in the universe and the build-up of stellar structures in these very early times”, explained Jonay Gonzalez Hernandez, senior researcher from Instituto de Astrofisica de Canarias.

“This exciting discovery illustrates the power of bringing together observers and theorists from across the world to share their enthusiasm and expertise”, said David Aguado from Cambridge’s Institute of Astronomy, who led the low-resolution spectroscopic analysis. “The international team led by Nicolas Martin and Kim Venn unveiled the remarkable globular cluster structure thanks to the combination of data from the Gaia spacecraft combined with observations from multiple ground-based telescopes”.

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Page last updated: 5 January 2022 at 17:20