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arXiv · 2604.01828

Milky-Way-like stars in a galaxy core 8 billion years ago revealed by gravitational lensing

Quirino D'Amato·Filippo Mannucci·Alessandro Sonnenfeld·Martina Scialpi·James W. Nightingale·Cristiana Spingola·Stefano Zibetti·Alessandro Marconi·Piero Rosati·Cosimo Marconcini·Guido Agapito·Anna Gallazzi·Enrico Di Teodoro·Gloria Andreuzzi·Francesco Belfiore·Elena Bertola·Caterina Bracci·Stefano Carniani·Elisa Cataldi·Avinanda Chakraborty·Matteo Ceci·Claudia Cicone·Anna Ciurlo·Giovanni Cresci·Alessandra De Rosa·Elisa Di Carlo·Anna Feltre·Michele Ginolfi·Isabella Lamperti·Bianca Moreschini·Emanuele Nardini·Michele Perna·Elisa Portaluri·Khatun Rubinur·Paolo Saracco·Paola Severgnini·Vincenzo Testa·Giulia Tozzi·Giacomo Venturi·Lorenzo Ulivi·Cristian Vignali·Maria Vittoria Zanchettin·Antonio Pepe
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Abstract

The assembly of stellar-dominated cores in elliptical galaxies is key to understanding how cosmic structures evolved. Gravitational lensing offers unique insights into the nature of their stars. We report the discovery of the smallest known quadruply lensed quasar (radius ~0.2"), whose lensing galaxy at redshift 1.055 (5.5 billion years after the Big Bang) features a lensing mass of only ~2x10^10 M_sun. A Bayesian analysis, based on the system's exceptional properties and standard scaling relations, allowed us to sample the central galactic initial mass function with unmatched accuracy and in a previously uncharted regime in terms of mass and redshift. We found it consistent with the Milky Way one, while excluding bottom-heavy functions. This suggests that the core either grew slowly or underwent early disruptive events altering its stellar build-up, in contrast with the classical view that bulges form rapidly and remain unchanged by later interactions.

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Quirino D'Amato, Filippo Mannucci, Alessandro Sonnenfeld, Martina Scialpi, James W. Nightingale, Cristiana Spingola, Stefano Zibetti, Alessandro Marconi, Piero Rosati, Cosimo Marconcini, Guido Agapito, Anna Gallazzi, Enrico Di Teodoro, Gloria Andreuzzi, Francesco Belfiore, Elena Bertola, Caterina Bracci, Stefano Carniani, Elisa Cataldi, Avinanda Chakraborty, Matteo Ceci, Claudia Cicone, Anna Ciurlo, Giovanni Cresci, Alessandra De Rosa, Elisa Di Carlo, Anna Feltre, Michele Ginolfi, Isabella Lamperti, Bianca Moreschini, Emanuele Nardini, Michele Perna, Elisa Portaluri, Khatun Rubinur, Paolo Saracco, Paola Severgnini, Vincenzo Testa, Giulia Tozzi, Giacomo Venturi, Lorenzo Ulivi, Cristian Vignali, Maria Vittoria Zanchettin, Antonio Pepe. 2026-04-02. Milky-Way-like stars in a galaxy core 8 billion years ago revealed by gravitational lensing. https://doi.org/10.1038/s41550-026-02819-4

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