Few stars have their own names. In this case, the name Earendel comes from Old English words meaning “morning star” or “rising light”. Fans of JRR Tolkien will remember that one of his characters The Silmarillion it has a very similar name – Eärendil – but that is pure coincidence. The amazing thing about Earendel is its remoteness. The light captured by the Hubble telescope was emitted when the universe was less than a billion years old. In other words, the light traveled through space for nearly 13 billion years before Hubble captured it. Earendel can only be seen under very specific conditions, which is why it was one of the main targets of James Webb, which launched on December 25, 2021. Fortunately, given the time of year, the telescope can see the southern constellation of Cetus containing Earendel. With its powerful resolution and infrared cameras, James Webb captured a new, even more detailed image of the star and the arc of light surrounding it on July 30. This arc of light, which makes the star appear brighter, also has a name: the Sunrise Arc.
Cosmic magnifying glass
In December, James Webb will again point its mirrors at Earendel in order to perform a spectral analysis to confirm or rule out the presence of heavy elements. So far, based solely on Hubble and James Webb images, more than 4,700 scientific articles have been published about the star. It is the most distant single object we can currently discern in the universe – although there are already reports of three or four other, very old stars that can be detected thanks to gravitational lensing. An image taken by Hubble, with the Arendelle Galaxy indicated by an arrow. NASA With stars that far away, astronomers don’t talk about distance but rather “redshift,” a measure of how much their light has been “stretched” as a result of the expansion of the universe. In the case of Earendel, this index is 6.2, meaning it is 28 billion light years from Earth. The star that held the previous record – nicknamed Icarus, in the constellation Leo – isn’t half that. It seems like a paradox: how is it possible to see an object at this distance when the universe has only existed for about 13.8 billion years? The starlight should not have reached us yet. The answer to this paradox is that space is not static, but rather expanding at an accelerating rate. When the light of Earendel began its journey, the universe was very young and therefore much smaller than it is now. Since then, space has been expanding and the distance between galaxies is getting bigger and bigger. What is also surprising about Earendel is that it is an isolated star, not a galaxy. The oldest galaxies do not appear in Hubble pictures as the beautiful spirals we know, but as irregular masses of reddish-hued gas in which no structure can be discerned. In fact, this color is the result of how images are rendered. Earendel is marked with a green star in an image from the Hubble Space Telescope.NASA Earendel is a massive star – or rather, it was, because it has been losing mass for centuries. It may be a legendary population III star, which first appeared after the Big Bang. These stars contain only primordial hydrogen and helium as atoms of other metals did not yet exist. These heavier atoms would form as a result of the nuclear reactions that occur during the evolution of these stars. Arendelle is estimated to be between 50 and a hundred times the mass of the Sun and to have a surface temperature of 20,000°C (36,000°F). This would make it extremely bright, with a blue-white glow. But no matter how bright it is, an isolated star should be invisible from such a distance. That we can see it is due to an unusual circumstance. Between the star and Earth is a small group of galaxies whose gravity acts like a lens that focuses and distorts light from more distant objects. Additionally, Earendel is located right in a narrow region of this giant magnifying glass where the gravitational lensing effect is greatest. Thanks to this phenomenon, the star’s light can be magnified between 1,000 and 40,000 times – enough to be detected by Hubble. That is, after the telescope has spent nine hours looking at the same area of the sky. Photon by photon, the telescope has captured the light from Earendel on its long journey through the universe.
