Two articles, one published in “The Astrophysical Journal” and one in “The Astrophysical Journal Letters”, report various aspects of a study of Earendel, the most distant single known star. Two teams of researchers with several members in common used observations conducted with the James Webb Space Telescope to obtain new details of this star, which even such a powerful instrument could only detect thanks to a gravitational lens. Officially cataloged as WHL0137-LS, the new study turns out to be a class B blue giant, much more massive than the Sun. Webb’s observations also reveal a luminous component that could belong to a less massive companion and not even the Hubble Space Telescope was able to detect.
The image (NASA, ESA, CSA. Science: Dan Coe (STScI/AURA for ESA, JHU), Brian Welch (NASA-GSFC, UMD). Processing: Zolt G. Levay) shows on the left, the galaxy cluster WHL0137-08 and in the inset, the galaxy nicknamed the Sunrise Arc in its distorted form, which hosts the star Earendel.
The identification of the star Earendel, announced in March 2022, aroused a lot of interest in the world of astronomy because it’s about 12.9 billion light-years away from Earth. The gravitational lensing effect magnified it at least 4,000 times, enabling first the Hubble Space Telescope to detect it and then the James Webb to study it even better.
The star Earendel is part of the galaxy cataloged as WHL0137-zD1 and nicknamed the Sunrise Arc due to the arc shape caused by the distortion of the gravitational lens which in turn is part of the galaxy cluster WHL0137-08. Precisely that cluster is at the origin of the gravitational lens effect that allowed these observations.
The James Webb Space Telescope’S NIRCam (Near-Infrared Camera) instrument made it possible to obtain new information about Earendel and the entire Sunrise Arc galaxy. Star clusters and star-forming regions were identified by Webb, and ancient globular clusters in the Milky Way likely resembled those star clusters a few million years after they formed.
The new observations of Earendel confirm that it’s a much more massive star than the Sun, a blue giant of the type that belongs to the spectral class B. The authors of the discovery hypothesized that it has a companion because this is typical of these stars but the Hubble Space Telescope found no trace of it.
Because of Earendel’s distance, its emissions have such a redshift that light from a possible less massive and therefore less hot companion reaches us at wavelengths longer than those detectable by Hubble. Webb is better and detected the possible emissions of a companion. However, the analyzes of the observations are not yet conclusive.
One conclusion regarding the galaxy cluster WHL0137-08 is that there is indeed a gravitational bond between the galaxies that make it up. The consequence is that it probably still exists today.
The studies based on data collected with the NIRCam instrument are very interesting and more data collected with NIRSpec (Near-Infrared Spectrograph), another instrument of the James Webb Space Telescope, is under analysis. The new phase of the study offers the possibility to more precisely measure the composition and distance of the galaxy Sunrise Arc and the star Earendel. This will help to understand if it’s a first-generation star and in any case, it will offer interesting new information on stellar formation and evolution when the universe was very young.
