Stellar ejecta gradually enrich the gas out of which subsequent stars form, making the least chemically enriched stellar systems direct fossils of structures formed in the early universe. Although a few hundred stars with metal content below one thousandth of the solar iron content are known in the Galaxy, none of them inhabit globular clusters, some of the oldest known stellar structures. These show metal content of at least ~0.2 percent of the solar metallicity ([Fe/H] > -2.7). This metallicity floor appears universal and it has been proposed that proto-galaxies that merge into the galaxies we observe today were simply not massive enough to form clusters that survived to the present day. Here, we report the discovery of a stellar stream, C-19, whose metallicity is less than 0.05 per cent the solar metallicity ([Fe/H]=-3.38 ± 0.06 (stat.) ± 0.20 (syst.)). The low metallicity dispersion and the chemical abundances of the C-19 stars show that this stream is the tidal remnant of the most metal-poor globular cluster ever discovered, and significantly below the purported metallicity floor: clusters with significantly lower metallicities than observed today existed in the past and contributed their stars to the Milky Way halo.
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Next week, from 5th to 9th September, the XV Scientific Meeting of the Spanish Astronomical Society (SEA) will take place in La Laguna, ion collaboration with the Instituto de Astrofísica de Canarias (IAC). In this edition 500 professional astronomers will be present. As well as the scientific programme, from this Saturday and throughout the week, there will be lectures, observations, and other activities open to the general public. This meeting, which is held every two years, was planned for 2020, but had to be substituted by a virtual meeting because of the pandemic. Now the professionalAdvertised on
Many of the most basic and important physical phenomena are determined by a set of “fundamental constants”, whose values are experimentally known to high accuracy. A key aspect is to know whether they are “universal constants”, i.e., whether they have always had the same value across the Universe and throughout its history. Here we made use of data from the ESPRESSO spectrograph on the Very Large Telescope (VLT) in order to determine the value of the fine structure constant 8 thousand million years ago (when the Universe was just 40% its current age) by measuring spectral transitions in aAdvertised on