Is Earendel a Star? Investigating the Sunrise Arc Using JWST Strong and Weak Gravitational Lensing Analyses

Abstract The galaxy cluster WHL J013719.8−08284 at z = 0.566 exhibits a strong-lensing feature known as the Sunrise Arc, which hosts Earendel, the most distant candidate star observed to date at z ≈ 6.2. If this object is a star, or a system of a few stars, its apparent magnitude implies both extreme gravitational lensing magnification and an unusually high luminosity. This study revisits Earendel’s magnification, which, in previous literature, exhibits significant uncertainty across various lens models (2 μ = 4​​​​​000–35,000). We present an improved cluster mass reconstruction and a tighter constraint on Earendel’s magnification using a joint strong- and weak-lensing analysis with JWST data. Our strong-lensing mass model, which incorporates newly identified multiple-image systems from JWST imaging data and modifies the existing multiple-image assignment scheme, yields an rms lens-plane scatter of less than <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>0</mml:mn> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>″</mml:mi> </mml:mrow> </mml:mover> <mml:mn>3</mml:mn> </mml:math> . Additionally, our weak-lensing catalog achieves a source density of ∼100 galaxies arcmin −2 , providing constraints on the mass profile beyond the strong-lensing regime. In our best-fit model, we estimate the magnification of Earendel to be μ = 43–67, significantly lower than previously proposed and thus calling into question its classification as a star.