Earendel, the farthest known star in the universe, is rediscovered by the 'James Webb'

Space Telescope

has grabbed front pages with its recent images, its predecessor, the venerable

, launched in 1990, is still operational and promoting new discoveries.

Like, for example, the observation in March of Earendel, the most distant star.

Few stars have their own names.

In this case, it is derived from archaic English and means, more or less, “dawn star”.

Fans of Tolkien's sagas will remember that one of the protagonists in

goes by a very similar name, but this is pure coincidence.

The surprising thing about Earendel is his remoteness.

The light

has captured was emitted when the universe was less than a billion years old, meaning it has been traveling through space for almost 13 billion years before leaving its faint trace on

's electro-optical sensors .

It is very unlikely that the circumstances that have allowed us to take this look at such an old star are given.

That is why, from the first moment, it was considered a first-order target for the

, launched on December 25, 2021. Fortunately, given the time of year, the southern constellation of the Whale where Earendel hides is within reach. of the telescope.

With its increased resolving power and ability to see in the infrared, the

took a new, even more detailed image on July 30, both of the star itself and of the arc of light surrounding it, which is responsible for the favorable optical effect that amplifies its brightness.

A trace of warped light that has also been given a name: Arc of the Dawn.

Cosmic magnifying glass and redshift

In December,

will point its mirror there again to attempt a spectral analysis to confirm or rule out the presence of heavy elements.

At the moment, and only with the

and

images, Earendel has already generated more than 4,700 articles in scientific publications (almost 40%, from authors associated with European institutions).

Not in vain is it the most remote individual object that —today— we can distinguish in the cosmos.

Although there are already reports that three or four more stars have been identified, very old and also favored by another cosmic "magnifying glass".

The image taken by the 'Hubble', with the galaxy where Earendel is indicated by an arrow.NASA

With stars so remote, astronomers don't talk about distance so much as "redshift," a measure of how much their light has been "dilated" as a result of the expansion of the universe.

In the case of Earendel, that index is 6.2, which places it 28 billion light-years from us.

The one that held the previous record – nicknamed Icarus, in the constellation of Leo – does not reach half that figure.

It seems like a paradox: How is it possible to see an object at that distance when the universe has existed for much less time?

His light, whose speed cannot exceed any physical body, should not have had time to reach us yet.

The answer is that space is not static, but is constantly expanding.

When Earendel's light began its journey, the universe was very young and therefore much smaller than it is now.

Since then, space has been growing and in its expansion it has been separating more and more the galaxies it contains.

Lonely Star

But what has surprised him most is that Earendel is an isolated star, not a galaxy.

The oldest galaxies do not appear in

photos as the pretty spirals we know, but as irregular masses of reddish-hued gas in which no structure is discernible.

In reality, this color is false, the result of the treatment of the images.

Most of the light they emit has migrated into the infrared, precisely because the expansion of space has

their wavelengths to that end of the spectrum.

The 'Hubble' image, with Earendel marked with a green star.NASA

Earendel is a huge star.

Rather, it was, because its fires have been out for eons.

It is likely to be a sample of the legendary Population III, the first stars to appear after the Big Bang.

They had to be formed only by primordial hydrogen and helium.

No other element was involved in its composition, for the simple reason that 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.

When they exploded, after a short and violent life, they would spread all those products throughout the cosmos that would serve as the building blocks of the next stellar generation.

It is estimated that Earendel had a mass between fifty and a hundred times greater than the Sun, with a surface temperature of 20,000 degrees (the Sun is only a third of that figure).

That would make it extremely luminous, with a bluish-white glow.

But no matter how bright, an isolated star that has not gone supernova should be invisible from such a distance.

That we can see it is due to an unusual chance.

Between that star and us stands a small group of galaxies whose gravity acts like a lens that both concentrates and distorts the light from more distant objects.

Furthermore, Earendel is precisely in a narrow area of ​​that giant magnifying glass where the light is strengthened the most.

In optics it is known as a

and in the telescope image it appears as a thin luminous arc.

It is the same effect that occurs at the bottom of a swimming pool, when the ripples of the water on the surface form brighter bands, or like light passing through a glass, which creates abstract shapes on the table.

Thanks to this effect, the star's light could be increased between a thousand and forty thousand times, enough for

to distinguish it.

Of course, after having accumulated nine hours of exposure looking towards the same region of the sky.

Literally, the telescope has been accumulating one by one the photons that arrive from Earendel after their long journey through the universe.

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