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. Here we report the discovery of an extremely compact quadruply lensed quasar (radius ~0.2″), whose lensing galaxy at a redshift of 1.055 (5.5 billion years after the Big Bang) features a lensing mass of only ~2 × 1010 M⊙. Bayesian analysis, based on the exceptional properties of the system and standard scaling relations, makes it possible to sample the central galactic initial mass function with great accuracy and in a previously uncharted regime in terms of mass and redshift. We find it to be consistent with the initial mass function of the Milky Way while excluding bottom-heavy functions. This indicates that the core either grew slowly or underwent early disruptive events altering its stellar build-up, potentially challenging the classical view in which bulges form rapidly and remain unchanged by later interactions.
Milky-Way-like stars in a galaxy core 8 billion years ago revealed by gravitational lensing / D'Amato Q., Mannucci F., Sonnenfeld A., Scialpi M., Nightingale J.W., Spingola C., Zibetti S., Marconi A., Rosati P., Marconcini C., Agapito G., Gallazzi A., Di Teodoro E., Andreuzzi G., Belfiore F., Bertola E., Bracci C., Carniani S., Cataldi E., Chakraborty A., et al.. - In: NATURE ASTRONOMY. - ISSN 2397-3366. - ELETTRONICO. - 10:(2026), pp. 901-912. [10.1038/s41550-026-02819-4]
Milky-Way-like stars in a galaxy core 8 billion years ago revealed by gravitational lensing
Scialpi M.;Zibetti S.;Marconi A.;Marconcini C.;Di Teodoro E.;Bracci C.;Cataldi E.;Ceci M.;Ginolfi M.;Lamperti I.;Moreschini B.;Tozzi G.;Ulivi L.;
2026
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. Here we report the discovery of an extremely compact quadruply lensed quasar (radius ~0.2″), whose lensing galaxy at a redshift of 1.055 (5.5 billion years after the Big Bang) features a lensing mass of only ~2 × 1010 M⊙. Bayesian analysis, based on the exceptional properties of the system and standard scaling relations, makes it possible to sample the central galactic initial mass function with great accuracy and in a previously uncharted regime in terms of mass and redshift. We find it to be consistent with the initial mass function of the Milky Way while excluding bottom-heavy functions. This indicates that the core either grew slowly or underwent early disruptive events altering its stellar build-up, potentially challenging the classical view in which bulges form rapidly and remain unchanged by later interactions.
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