Earendel is a B-type giant star, a luminous blue variable star, or even a binary system with an extremely hot primary member, according to new observations from the NASA/ESA/CSA James Webb Space Telescope.
Earendel, also known as WHL0137-LS, is a giant star located in the constellation of Cetus.
The star was first identified in Hubble images taken as part of the Reionization Lensing Cluster Survey (RELICS) program.
Nicknamed after the Old English word for ‘morning star’ or ‘rising light,’ Earendel is magnified by a factor of several thousands by the foreground galaxy cluster WHL0137-08.
“Massive galaxy clusters magnify the distant Universe through strong gravitational lensing,” said Johns Hopkins University astronomer Brian Welch and his colleagues wrote in their paper.
“These cosmic telescopes provide improved spatial resolution over what cutting-edge telescopes can provide alone, allowing the identification of small-scale structures in high redshift galaxies.”
“In certain cases of precise alignment, galaxy clusters can magnify the light from individual stars by factors of thousands, allowing these stars to be seen above the light of their host galaxies.”
“The first of these were discovered as transients in Hubble images, at redshifts ranging from z=1-1.5.”
“Recent discoveries have pushed lensed star observations to greater distances, including recent discoveries at a redshift of z=2.37, another at z=2.65 with Webb, and a star at z=6.2 discovered in Hubble imaging.”
The new Webb observations support the previous conclusion that Earendel is an extremely magnified star at redshift of z=6.2, meaning its light departed 12.9 billion years ago.
“The increased spatial resolution of Webb allows us to improve our constraints on the total magnification of the star, resulting in best-fit values ranging from 6,000 to 35,000,” the astronomers wrote.
“This further distinguishes Earendel from known young massive star clusters, which have typical radii of 1 parsec.”
“Even small central cores observed in nearby star clusters such as R136 do not reach below tenths of a parsec, which is still far larger than our measured radii,” they added.
“This strengthens our conclusion that Earendel is most likely an individual star system.”
According to the authors, Earendel has a mass between 20 and 200 solar masses and a temperature up to 16,000 K.
“If the light of Earendel is dominated by a single star, it likely has an effective temperature of T=13,000-16,000 K, indicating that it is likely a B-type giant similar to other lensed stars, or perhaps a luminous blue variable star,” they wrote.
“The apparent discrepancies between our best-fit single star model and the observed photometric data allow room for the consideration of multi-star models.”
“In particular, we note that a two-star system with one hot (T=30,000 K) and one cooler (T=10,000 K) star could produce a better fit to the observed data, though the wide parameter space in this case allows for many similarly well-matched solutions,” they added.
“These initial photometric constraints, while themselves inconclusive, provide an important guide for our upcoming spectroscopic observations.”
“Spectroscopic observations with Webb’s Near-Infrared Spectrograph (NIRSpec), expected in December 2022, can help to address these discrepancies and further constrain the temperature and luminosity of the star/stars.”
The team’s paper will be published in the Astrophysical Journal.
Brian Welch et al. 2022. JWST Imaging of Earendel, the Extremely Magnified Star at Redshift z=6.2. ApJ, in press; arXiv: 2208.09007
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