Earendel (WHL0137-LS) is the earliest and most distant star discovered to date. It lies at a comoving distance of 28 billion light-years from Earth. It is almost twice as distant as the previous record holder, Icarus (MACS J1149 Lensed Star 1). Earendel lies in the constellation Cetus. It was discovered by the Hubble Space Telescope through a gravitational lens. The discovery was reported on March 20, 2022.
Hubble was able to detect Earendel because the star’s light was lensed by the galaxy cluster WHL0137-08, which lies between us and the star. The massive cluster acted like a magnifying glass, amplifying the star’s light between 1,000 and 40,000 times.
Earendel’s host galaxy, catalogued as WHL0137-zD1, was nicknamed “Sunrise Arc” because gravitational lensing bent its light into the shape of a long crescent. The two red dots visible on either side of WHL0137 Lensed Star are both the same star cluster whose light has been bent into two separate images that mirror each other.
Earendel has a redshift of 6.2. The light detected from the star was emitted only 900 million years after the Big Bang, and it reached Earth 12.9 billion years later. However, the comoving distance – which takes into account the expansion of the universe in the time since the light was emitted – is now 28 billion light years.
When the starlight from Earendel was emitted, the star was only 4 billion light-years away from what became the Milky Way galaxy. As the universe expanded during the 12.9 billion years that it took for the light to reach Earth, the star would now be 28 billion light years away.
The previous record holder for the most distant single star – Icarus (MACS J1149 Lensed Star 1) – has a comoving distance of 14.4 billion years with a redshift of 1.49. Its light was emitted 9.34 billion years ago, about 4.4 billion years after the Big Bang.
Earendel is a hot blue star with a mass between 50 and 100 times that of the Sun and a surface temperature of at least 20,000 K. Beyond that, its properties are uncertain. Stars with such high mass do not live very long lives. They burn through their supply of hydrogen quickly and evolve away from the main sequence to become supergiants. Earendel likely went out as a supernova only a few million years after forming.
There is a small probability that Earendel is a population III star. Population III stars are a hypothetical group of exceptionally massive, hot, luminous stars that existed when the universe was very young. These stars contained almost no metals. They were made almost entirely of primordial hydrogen and helium. They are believed to have started the production of chemical elements heavier than hydrogen, essential for the formation of planets.
The earliest generation of stars formed about 100 million years after the Big Bang, which means that Earendel was preceded by one or two generations of stars. Heavier elements did not exist before these first stars went out as supernovae.
The James Webb Space Telescope, launched on December 25, 2021, will be able to provide a better look at Earendel and better pinpoint its properties. Astronomers expect that the star will stay magnified for years to come. The space telescope has the sensitivity to allow a more detailed analysis of Earendel’s stellar spectra and detect any companions. The data collected with it will allow scientists to constrain Earendel’s mass, radius, temperature, and age, as well as to confirm if it is a single star.
The detection of the first generation of stars is one of the most important objectives of the James Webb telescope. If astronomers find that Earendel is indeed made only of primordial hydrogen and helium, this will be the first detection of a Population III star.
The discovery of WHL0137-LS, a star at redshift 6.2, was reported on March 30, 2022. The study was published in the journal Nature. Earendel was found by a team led by astronomer Brian Welch of the Johns Hopkins University in Baltimore. It was detected in Hubble’s exposures taken on June 7, 2016, July 17, 2016, November 4, 2019, and November 27, 2019.
The data was collected during Hubble’s Reionization Lensing Cluster Survey (RELICS) program, led by co-discoverer Dan Coe of the Space Telescope Science Institute (STScI). The RELICS program aimed at discovering high-redshift galaxies that existed in the early universe. The observations that led to the discovery of the highest redshift star focused on massive clusters of galaxies that acted as lenses for high-redshift galaxies.
The name Earendel comes from the Old English name for “rising light” or “morning star.” The name is also a reference to Eärendil the Mariner, a half-elven character in J. R. R. Tolkien’s The Silmarillion (1977) and Unfinished Tales (1980). In Tolkien lore, Eärendil carries the last of the Silmarils (jewels composed of the light of the Two Trees), which becomes the Morning Star.
The star was named by the researchers who discovered it. They explained that it was a good fit for a star that existed during the Cosmic Dawn, a period when the first stars, black holes and galaxies started to form. The period lasted from about 50 million years to one billion years after the Big Bang.
Earendel lies in the central region of the constellation Cetus, above the imaginary line connecting Zeta and Theta Ceti. With an apparent magnitude of 27.2, the star is invisible even in the largest amateur telescopes.
Earendel is located in the constellation Cetus. In Greek mythology, Cetus is associated with the sea monster from the myth of Andromeda. It was one of the 48 Greek constellations, catalogued by the Greco-Roman astronomer Ptolemy in his Almagest in the 2nd century CE.
Cetus is the fourth largest constellation in the sky (after Hydra, Virgo, and Ursa Major), occupying 1,231 square degrees of the mostly southern sky. It is one of the 15 equatorial constellations, visible from most locations for at least part of the year. Despite its size, Cetus does not stand out in the night sky. Only two of its stars – Diphda and Menkar – shine brighter than magnitude 3.00.
Cetus hosts many interesting stars, among them Tau Ceti, the nearest Sun-like star to Earth, UV Ceti (Luyten 726-8B), a nearby flare star, and Mira (Omicron Ceti), a famous pulsating variable red giant.
Cetus contains several relatively bright deep sky objects. These include the barred spiral galaxy Messier 77 (Cetus A), the spiral galaxies NGC 247, NGC 1042, NGC 1035 and NGC 1055, the irregular dwarf galaxy IC 1613, and the planetary nebula NGC 246 (the Cetus Ring).
The best time of year to see the stars and deep sky objects in Cetus is during the month of November, when the constellation rises high above the horizon in the evening sky. The entire constellation is visible from locations between the latitudes 70° N and 90° S.
The 10 brightest stars in Cetus are Diphda (Beta Ceti, mag. 2.02), Menkar (Alpha Ceti, mag. 2.53), Eta Ceti (mag. 3.446), Kaffaljidhma (Gamma Ceti, mag. 3.47), Tau Ceti (mag. 3.50), Iota Ceti (mag. 3.562), Theta Ceti (mag. 3.60), Baten Kaitos (Zeta Ceti, mag. 3.742), Upsilon Ceti (mag. 3.95), and Delta Ceti (mag. 4.06). The pulsating variable star Mira (Omicron Ceti, mag. 2.0 – 10.1) is sometimes among the brightest stars in the constellation and at other times it is invisible to the naked eye.
Earendel – WHL0137-LS
|Distance||28 billion light years|
|Mass||50 – 100 M☉|
|Right ascension||01h 37m 23.232s|
|Declination||–8° 27′ 52.20″|
|Names and designations||Earendel, WHL0137-LS|