Quantifying tensions - inconsistencies amongst measurements of cosmological parameters by different experiments - has emerged as a crucial part of modern cosmological data analysis. Statistically significant tensions between two experiments or cosmological probes may indicate new physics extending beyond the standard cosmological model and need to

Extragalactic astronomy and stellar astrophysics are intrinsically related. In fact, the determination of important galaxy properties such as stellar masses, star formation histories, or chemical abundances relies on the ability to model their stellar populations. One important ingredient of these models is stellar libraries. Empirical libraries

Among the low-mass pre-main sequence stars, a small group called FU Orionis-type objects (FUors) are notable for undergoing powerful accretion outbursts. V1057 Cyg, a classical example of an FUor, went into outburst around 1969-1970, after which it faded rapidly, making it the fastest-fading FUor known. Around 1995, a more rapid increase in fading

Obscuration and confusion conspire to limit our knowledge of the inner Milky Way. Even at moderate distances, the identification of stellar systems becomes compounded by the extremely high density of background sources. Here, we provide a very revealing example of these complications by unveiling a large, massive, young cluster in the Sagittarius

Stellar activity and rotation are tightly related in a dynamo process. Our understanding of this mechanism is mainly limited by our capability of inferring the properties of stellar turbulent convection. In particular, the convective turnover time is a key ingredient through the estimation of the stellar Rossby number, which is the ratio of the

Although true metal-free "Population III" stars have so far escaped discovery, their nature, and that of their supernovae, is revealed in the chemical products left behind in the next generations of stars. Here we report the detection of an ultra-metal-poor star in the Sculptor dwarf spheroidal galaxy AS0039. With [Fe/H] LTE = -4.11, it is the most