James Webb Looked at the Most Distant Star Ever Seen. What It Found Broke the Models.

In 2022, a Johns Hopkins graduate student named Brian Welch was sifting through archival Hubble Space Telescope images of a massive galaxy cluster when he found something that should not have been there: a single point of light on a gravitational lensing arc, steady and bright, in a position that made it a candidate for the most distant individual star ever detected. The star is 12.9 billion light-years away, its light having left when the universe was only 900 million years old, roughly six percent of its current age. Tonight, we follow everything that has been found and argued and revised about that point of light. We begin with Brian Welch and the discovery, the RELICS survey, the 2016 Hubble exposures, and the nature of the galaxy cluster WHL0137-08 whose gravity bent and magnified the star's light by thousands of times. We cover gravitational lensing from Einstein's 1915 prediction through Eddington's 1919 eclipse confirmation to its modern use as a natural telescope for seeing individual stars across cosmological distances. We examine the Sunrise Arc, the lensing structure that made Earendel visible, and what Hubble could tell us about the star's nature and what it could not. We follow the James Webb Space Telescope's follow-up observations with NIRCam, the colors and temperatures they revealed (13,000 to 16,000 degrees Kelvin, consistent with a massive hot blue star), the discovery of a likely companion star, and what the mass estimates (20 to 200 solar masses) mean for stellar physics in the early universe. We cover Population III stars, the first stars made only of hydrogen and helium, never yet directly confirmed, and whether Earendel could be one or a cluster of them. We examine the 2025 papers that revised the lensing magnification sharply downward and reopened the question of whether Earendel is a single star at all or a metal-poor globular cluster progenitor. We follow the name itself, from the Old English poem Crist through Tolkien's Earendil the Mariner to Brian Welch's naming choice for the furthest point of light any star has ever sent us. And we meet the growing family of extreme lensed stars, Quyllur, Mothra, Icarus, that Earendel's discovery opened the door to finding. Sources: Welch, B. et al. (2022). A Highly Magnified Star at Redshift 6.2. Nature, 603, 815-818. Welch, B. et al. (2023). JWST Imaging of Earendel, the Most Highly Magnified Star at Cosmological Distances. arXiv:2208.09007 Pascale, M. et al. (2025). Is Earendel a Star or a Star Cluster? arXiv:2507.05483 Diego, J.M. et al. (2023). JWST/NIRCam Probes Young Star Clusters in the Sunrise Arc. The Astrophysical Journal. NASA Science (2022). Record Broken: Hubble Spots Farthest Star Ever Seen. science.nasa.gov NASA Science (2022). Webb Reveals Colors of Earendel, Most Distant Star Ever Detected. science.nasa.gov Quyllur: Diego, J.M. et al. (2022). A&A, Quyllur Red Supergiant Discovery. Mothra: Diego, J.M. et al. (2023). Mothra Kaiju Star. A&A.