A Highly Magnified Star at Redshift 6.2

TL;DR

This paper reports the discovery of a highly magnified star at redshift 6.2, observed over 3.5 years, providing insights into early universe stars and gravitational lensing effects.

Contribution

It presents the first persistent observation of a magnified star at such a high redshift, demonstrating the potential of gravitational lensing to study early universe stellar populations.

Findings

Star at z=6.2 magnified by a factor of thousands

Brightness remained stable over 3.5 years

Consistent with a star of mass >50 solar masses

Abstract

Galaxy clusters magnify background objects through strong gravitational lensing. Typical magnifications for lensed galaxies are factors of a few but can also be as high as tens or hundreds, stretching galaxies into giant arcs. Individual stars can attain even higher magnifications given fortuitous alignment with the lensing cluster. Recently, several individual stars at redshift $z \sim 1 - 1.5$ have been discovered, magnified by factors of thousands, temporarily boosted by microlensing. Here we report observations of a more distant and persistent magnified star at redshift $z_{\rm phot} = 6.2 \pm 0.1$, 900 Myr after the Big Bang. This star is magnified by a factor of thousands by the foreground galaxy cluster lens WHL0137--08 ($z = 0.566$), as estimated by four independent lens models. Unlike previous lensed stars, the magnification and observed brightness (AB mag 27.2) have remained roughly constant over 3.5 years of imaging and follow-up. The delensed absolute UV magnitude $M_{UV} = -10 \pm 2$ is consistent with a star of mass $M > 50 M_{\odot}$. Confirmation and spectral classification are forthcoming from approved observations with the James Webb Space Telescope