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Almost 13 billion light years is an astonishing distance even for a telescope as sharp as Hubble. Usually, at such a distance, its optics can only see large galaxies, each of which has millions of stars. And yet NASA’s space observatory managed to make out the ancient star Earendel at the edge of the universe – thanks to a physical phenomenon predicted by the theory of relativity.
When the light from a distant star “bumps” on its way into some massive (by cosmic standards) object – for example, a neutron star or a cluster of galaxies – the gravitational field created by this object bends the space around it, changing the path of light rays, as in As a result, they go around, while receiving an additional impulse.
In science, this phenomenon is known as “gravitational lensing” because the massive body here acts as a lens and amplifies light rays.
Usually, with this method, scientists discover distant galaxies, but in this case a single star was lucky: its light rays were amplified so much that they hit the telescope.
“We were just incredibly lucky,” Brian Welch, an astrophysicist at Johns Hopkins University in Maryland, told the BBC. “If you find the right spot, as in our case, the increase is a thousandfold.”
The previous distance record was held by a star called Icarus. Hubble found it too – at a distance of “only” 9 billion light years from Earth.
Arendel is much further away, and we are observing the star at a time when about 900 million years have passed since the Big Bang, and the universe was in its infancy.
By the way, the name of the star Arendel (in fact, it is officially called not so romantically – WHL0137-LS) has nothing to do with the magical kingdom of Arendel from the Disney cartoon Frozen, but comes from the old English word meaning “morning star”. Yes, and in the Hubble image it is more likely to be just a faint point.
Another thing is that in the eyes of the astronomers who discovered it, Arendel looks completely different. At the same time, they willingly admit that they still know little about this star. They can’t even say for sure how big it is: it’s clear that it’s at least 50 times bigger than our sun, that is, one of the biggest stars discovered so far, but it may turn out that it’s actually much bigger, times at 500!
It is also possible that Hubble discovered the so-called double star, that is, in fact two stars whose orbits are close to each other. This is a very common phenomenon, but in this case one of the stars must be significantly more massive than the other, and it is its light signal that will dominate.
However, there is an alternative explanation: Arendel is not actually a distant star, whose light was refracted and amplified, passing by a cluster of galaxies, and an object in the foreground with a star-like light signature, for example, a brown dwarf. However, this is unlikely, since over 5 years of observations the object remained static, while the much closer dwarf should have moved slightly in space.
One of the most fascinating mysteries is the composition of the new old star. Astronomers have reason to believe that Arendel is one of the primary stars formed from the primordial gas that arose as a result of the Big Bang.
The theory says that the first stars consisted only of hydrogen and helium, but this caused them to burn out quickly over a few million years, after which they collapsed. And only after the stars “grabbed” heavy elements, outer space began to look like we are used to.
But if Arendel is indeed a primary star, then it could only be 900 million years after the Big Bang if it formed from an isolated, undiluted gas cloud – and this, while possible, is still highly unlikely.
“We suspect that Arendel is likely enriched in heavy elements a little, but not to the same extent as the stars that surround us today,” explains Welch. “There is even a small chance that this is the so-called population III star [к гипотетическому населению III принято относить первое после Большого взрыва поколение тяжелых звезд, которые, опять же в теории, не дожили до наших времен]. According to some theories, such stars can still be found on the outskirts of some galaxies.”
If astronomers are destined to find such stars, Hubble’s successor, the James Webb Space Telescope, launched last December and armed with much more advanced equipment, will be able to do so.
James Webb will be fully operational in a couple of months, and Brian Welch and colleagues have already had time to work with the new space observatory to take a closer look at Arendel.
By the way, no one is going to write off the old Hubble either. Although it was launched back in 1990 and is somewhat outdated, this telescope continues to help scientists make great discoveries.
“The Hubble telescope is doing great,” said NASA employee Dr. Jennifer Weissman. “It is powerful, it has a high scientific performance, and we hope that Hubble will make many more discoveries in the future. And, of course, we are very happy that it will work in parallel with James Webb. With these two telescopes at hand we can learn much more about the universe than we have been able to do so far.”