Friday, March 29

The Hubble telescope detects the oldest and most distant star: Eärendel


An international team of astronomers, led by Brian Welch from Johns Hopkins University (USA) and with the participation of researchers from the CSIC and the University of the Basque Country, has detected Earendel, the most distant star ever observed. The finding is published in the journal Nature.

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“Eärendel existed in the first billion years of the universe, during the big bang, and its light has traveled 12.9 billion years until reaching Earth”, explains one of the authors, Jose Maria Diegoresearcher at the Physics Institute of Cantabria (IFCA, CSIC-UC).

The star no longer exists, it exploded millions of years ago, but its light was so powerful that it is still visible and has been detected by the Hubble Space Telescope. It shone when the universe was young, just a billion years after the big bang (which occurred 13.8 billion years ago), and was much more massive and brighter than the Sun.

The discovery of Eärendel, located 12.9 billion light-years away, far exceeds the discovery of the farthest star observed to date: Icarus, located by Hubble at 9 billion light-years

Eärendel’s discovery far exceeds the finding of the farthest star observed to date: icarus, detected in 2018 by the Hubble Space Telescope at 9,000 million light years. It also opens a window to learn about the early days of the universe and the origin of the first star formations.

“His discovery represents a great leap back in time when compared to the previous Icarus record; it allows us to go back much further to the origin of the universe”, Diego points out, “in fact, Eärendel is the farthest star we know of, although it no longer exists. It exploded long ago but we still see the light that comes from it. We have been able to detect it thanks to the fact that it is magnified by a cluster of galaxies; if not, it would be impossible”.

The star gets its name from the poem Earendel’s journeythe evening star, written in 1914 by John Ronald Reuel Tolkien, author of The Lord of the ringswhich was inspired by Anglo-Saxon mythology.

A star magnified by gravitational lensing

As the universe expands, light from distant objects is stretched or shifted to longer wavelengths as they approach Earth. Until now, the objects observed at such a great distance respond to clusters of stars embedded within the first galaxies.

We have been able to detect it thanks to the fact that it is magnified by a cluster of galaxies; if not, it would be impossible

Jose Maria Diego
(IFCA, CSIC-UC)

“Normally, at these distances, galaxies are seen as small spots, because the light from millions of stars is mixed,” says Diego, “and the galaxy hosting Eärendel it has been magnified and distorted by gravitational lensing.”

“Just as curved glass distorts the image when we look through it, a gravitational lens amplifies the light from very distant objects aligned behind a cluster of galaxies. These galaxies are the ones that deflect the light of distant stars because their enormous mass deforms the space-time around them”, explains the researcher.

The team estimates that Eärendel would be at least 50 times the mass of the Sun, and that it would be much brighter than the Sun, thus rivaling the most massive known stars.



“Are primordial stars (which form from the elements that were forged shortly after the big bang: hydrogen, helium, and trace amounts of lithium), have so far eluded observers, but could now be detected if viewed through high-power gravitational lensing, as in the case of Eärendel”, comments Welch.

The team estimates that Eärendel would be at least 50 times the mass of the Sun, and that it would be much brighter than the Sun, thus rivaling the most massive known stars.

“They are first generation and we hardly knew anything about them. From now on, with stars like this, we will be able to study them in detail with telescopes like the james webb. In fact, there is already an observing program approved by NASA and in which we participate, ”he adds.

“Studying Eärendel will be a window into an era of the universe that we are not familiar with, but which led to everything we know. It is as if we have been reading an interesting book, but we start in the second chapter and now we have the opportunity to see how it all began, “completes Welch.

For her part, the researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC) and co-author Yolanda Jimenez Teja explains that “to predict whether Eärendel will remain bright for years to come or if it is temporary, we need to estimate the mass of all the stars that are in the line of sight between us and Eärendel.”

The expected contribution of James Webb

Since the data indicates that the star will continue to shine for years, the next step would be to study it with the James Webb Space Telescope. Astronomers hope that in 2022 Eärendel will be able to see itself increasingly enlarged with this observatory, launched at the end of 2021 and led by the American, European and Canadian space agencies (NASA/ESA/CSA).

With the Webb telescope it will be possible to know more about the composition of this star, a topic of special interest to astronomers because it was formed before the universe was filled with heavy elements

“Webb’s images and spectra will allow us to confirm that Eärendel is in fact a star and narrow down its age, temperature, mass and radius”, explains Diego. Welch adds that “combining the Hubble and Webb observations will also allow us to learn about microlensing in the galaxy cluster, which could include exotic objects such as primordial black holes”.

In addition, with the telescope it will be possible to know more about the composition of this star, a subject of special interest to astronomers because it was formed before the universe was filled with heavy elements, produced by several generations of massive stars.

“We are going to learn many things: we will obtain the spectrum, that is, the fingerprint of a star, it will tell us how old it is, how long ago it was born, how long it was alive when the light we see now was emitted, its metallicity or the elements that compose it”, concludes Diego.





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