Astronomers discover less metallic star system in the Milky Way

The structure found in the Milky Way has a lower proportion of heavy elements than any other. star system known in our galaxy… Discovery described in a scientific article published this Wednesday (5) in the journal Naturewas made through the Gemini Observatory, a program of the US National Optical Infrared Astronomy Research Laboratory (NOIRLab).

According to observations, the stars in this stream were detached from the ancient star cluster and are relics of the early days of the Milky Way, which may provide data on the formation of the first stars.

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An international team of researchers, including members of the European Union, Canada and Russia, is responsible for the discovery of C-19, the so-called stellar stream south of the Milky Way. Its orbit extends about 20,000 light years from the galactic center at its closest point and about 90,000 light years from the farthest point.

The star system covers an area equivalent to 30 full moons in the Milky Way.

According to scientists, the star system occupies an impressive area in the night sky – about 30 times the width. Key – although not visible to the naked eye.

Using the Gemini North Telescope in Hawaii and the Gemini Remote Access to CFHT SPADES Spectrograph (GRACES) instrument, both from the Gemini Observatory, the team realized that C-19 was the remnant of a globular cluster.

Globular clusters were previously thought to contain at least 0.2% metal, but C-19 has an unprecedented level of less than 0.05% metallicity.

The discovery that a weak metallic flux arises from a globular cluster has implications for star formation. clusters stars and galaxies in the early universe.

In fact, the very existence of this stream indicates that globular clusters and the first building blocks of the Milky Way must have formed in a low-metal environment before successive generations of stars supplied the universe with heavier elements.

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“It is not known if globular clusters exist with so few heavy elements. Some theories even suggested that they could not have formed, ”commented Nicholas Martin of the Astronomical Observatory in Strasbourg, the main author of the study. “Other theories suggest that they all disappeared long ago, making this a fundamental discovery for our understanding of how stars formed in the early universe.”

The team members originally detected C-19 in data from the Gaia satellite using an algorithm they developed specifically to detect stellar streams. The stars in C-19 were also identified by the Pristine Survey – a search for the least metallic stars in and around the Milky Way with the Canada-France-Hawaii telescope – as interesting enough to warrant follow-up observations.

To determine the origin of the stars that make up C-19, astronomers needed detailed GRACES spectra. The team also collected data using a spectrograph installed at the Gran Telescopio Canarias in La Palma, Canary Islands.

“GRACES provided important clues to the fact that C-19 is a discontinuous globular cluster rather than a more ordinary interrupted dwarf galaxy,” explained Kim Venn of the University of Victoria, principal investigator of the GRACES observations. “We already knew that this was a very low metal stream, but identifying it as a globular cluster required the precision of metallicity and detailed chemistry available only with high resolution spectra.”

The new study also suggests that C-19 must have formed from very early generations of stars, making the cluster a remarkable relic from when the first star clusters formed.

Consequently, this discovery improves our understanding of the formation of stars and star clusters that emerged shortly after the Big Bang, and provides a natural laboratory for studying the oldest structures in galaxies.

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