Extreme magnification of an individual star at redshift 1.5 by a galaxy-cluster lens

Patrick L. Kelly , Jose M. Diego , Steven Rodney , Nick Kaiser , Tom Broadhurst , Adi Zitrin , Tommaso Treu , Pablo G. Pérez-González , Takahiro Morishita , Mathilde Jauzac , Jonatan Selsing , Masamune Oguri , Laurent Pueyo , Timothy W. Ross , Alexei V. Filippenko , Nathan Smith , Jens Hjorth , S. Bradley Cenko , Xin Wang , D. Andrew Howell , Johan Richard (1) , Brenda L. Frye , Saurabh W. Jha , Ryan J. Foley , Colin Norman , Marusa Bradac , Weikang Zheng , Gabriel Brammer , Alberto Molino Benito , Antonio Cava , Lise Christensen , Selma E. de Mink , Or Graur , Claudio Grillo , Ryota Kawamata , Jean-Paul Kneib , Thomas Matheson , Curtis Mccully , Mario Nonino , Ismael Pérez-Fournon , Adam G. Riess , Piero Rosati , Kasper Borello Schmidt , Keren Sharon , Benjamin J. Weiner

1 CRAL - Centre de Recherche Astrophysique de Lyon

Galaxy-cluster gravitational lenses can magnify background galaxies by a total factor of up to ~50. Here we report an image of an individual star at redshift z = 1.49 (dubbed MACS J1149 Lensed Star 1) magnified by more than ×2,000. A separate image, detected briefly 0.26″ from Lensed Star 1, is probably a counterimage of the first star demagnified for multiple years by an object of ≳3 solar masses in the cluster. For reasonable assumptions about the lensing system, microlensing fluctuations in the stars’ light curves can yield evidence about the mass function of intracluster stars and compact objects, including binary fractions and specific stellar evolution and supernova models. Dark-matter subhaloes or massive compact objects may help to account for the two images’ long-term brightness ratio.

Domaines: Astrophysique [astro-ph]

Patrick L. Kelly, Jose M. Diego, Steven Rodney, Nick Kaiser, Tom Broadhurst, et al.. Extreme magnification of an individual star at redshift 1.5 by a galaxy-cluster lens. Nature Astron., 2018, 2 (4), pp.334-342. ⟨10.1038/s41550-018-0430-3⟩. ⟨hal-01797824⟩