James Webb Telescope rediscovers Earndale, the farthest known star in the universe | Science and Technology

Although the new James Webb Space Telescope has made headlines with its recent images of deep space, its predecessor, the venerable Hubble Space Telescope, launched in 1990, is still in operation and spurs new discoveries, for example, the Mars observation of Arendelle, The farthest known star in the universe.

Few stars have their own names. In this case, the name Earendel is derived from Old English words meaning “morning star” or “rising light”. JRR Tolkien fans will remember that one of the characters in Silmarlion It has a very similar name – Eärendil – but this is purely a coincidence.

The amazing thing about Earendel is its distance. The light captured by the Hubble telescope was emitted when the universe was less than a billion years old. In other words, light had been traveling through space for nearly 13 billion years before Hubble caught it.

Earendel can only be seen under very specific conditions, which is why one of the main targets of James Webb, which was launched on December 25, 2021. Fortunately, given the time of year, the telescope can see the southern constellation of Cetus that contains the Earendel. Thanks to powerful resolutions and infrared cameras, James Webb captured a new, more detailed image of the star and its arc of light on July 30. This arc of light, which makes a star appear brighter, is called the sunrise arc.

cosmic magnifying glass

In December, James Webb will again point its mirrors at Earendel in order to perform a spectroscopic analysis to confirm or rule out the presence of heavy elements. To date, based on only Hubble and James Webb images, more than 4,700 scientific articles have been published about the star. It is the most distant individual object that we can currently discern in the universe – although there are already reports of three or four other stars, identifiable thanks to a gravitational lens.

Image taken by Hubble, with the Earndale Galaxy indicated by an arrow.
Image taken by Hubble, with the Earndale Galaxy indicated by an arrow.NASA

With stars so far away, astronomers don’t talk about distance but rather their “redshift,” a measure of how much their light “expands” as a result of the expansion of the universe. In the case of Earendel, this index is 6.2, which means that it is 28 billion light years from Earth. The star that held the previous record – nicknamed Icarus, in the constellation Leo – is not half that number.

It seems like a paradox: How can an object be seen at that distance when the universe has been around for about 13.8 billion years? There shouldn’t be time for starlight to reach us yet.

The answer to this paradox is that space is not static, but rather expanding at an accelerating rate. When the Earndel Light began its journey, the universe was very young and therefore much smaller than it is now. Since then, space has expanded and the distance between galaxies has become larger and larger.

What’s surprising about Earendel is that it’s a solitary star, not a galaxy. The oldest galaxies do not appear in the Hubble images as the beautiful spirals we know, but rather as irregular masses of red-colored gas in which no structure can be distinguished. In fact, this color is a result of how the images are presented.

Earndel featured a green star in an image from the Hubble Space Telescope.
Earndel featured a green star in an image from the Hubble Space Telescope.NASA

Earndel is a huge star – or rather, it was, because it lost mass over eons. It may be the legendary Population III star, which was the first to appear after the Big Bang. These stars only contain primordial hydrogen and helium because atoms of other metals did not exist yet. These heavier atoms are formed as a result of nuclear reactions that occur during the evolution of these stars.

It is estimated that Earendel’s mass is 50 to 100 times greater than the Sun, and that its surface temperature is 20,000 °C (36,000 °F). This would make it very bright, with a bluish-white glow. But no matter how bright it is, the isolated star should be invisible from this distance.

What we can see is due to an unusual circumstance. Between the star and the Earth is a small group of galaxies whose gravity acts as a lens that focuses and distorts light from distant objects.

Moreover, Earendel is located precisely in a narrow region of that giant magnifying glass where the effect of the gravitational lens is greatest. Thanks to this effect, the star’s light can be amplified between 1,000 and 40,000 times – enough to be detected by Hubble. That is, after the telescope spent nine hours looking at the same area of ​​the sky. Photon by photon, the telescope captured light from Earndale on its long journey through the universe.

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