image source, NASA, ESA, Brian Welch (JHU), Dan Coe (STScI)
Caption,
Image of the galaxy that hosted the primordial star Eärendel.
Eärendel is the farthest individual star ever observed to date.
It owes its name to the poem written by Tolkien in 1914, Earendel’s journeyinspired by Anglo-Saxon mythology.
But what can a star that no longer even exists teach us regarding the life and death of its fellow creatures? And regarding the Big Bang?
According to the calculations of the authors of this important discovery, published in the journal Nature, Eärendel it would have 50 times the mass of the Sun and would have formed 900 million years following the Big Bang.
Actually, it supposes a small time compared to the age of the universe, of regarding 13.800 million years.
This would imply that the light emitted by this very old star, collected by the Hubble Space Telescope, would have traveled for regarding 12.8 billion years.
Eärendel would have formed 900 million years following the Big Bang.
In that time Eärendel has ceased to exist: it exploded at some point in the past, when it ran out of stellar fuel.
Before delving into the possible consequences of this discovery, we are going to review some basic aspects of the life and evolution of a star.
stellar evolution
We can imagine the life of a star as that of a living being: as they age, they undergo changes in their structure and composition.
A star originates when molecular clouds (which are galactic regions abundant in hydrogen at very low temperature) collapse due to their own gravitational attraction, fragmenting into smaller pieces.
When the density and temperature of these fragments is high enough, a nuclear fusion reaction is triggered.
This releases a huge amount of radiation, in addition to transforming hydrogen into helium.
As long as the star has enough hydrogen to burn, the pressure of the emitted radiation can compensate for the star’s own gravity, which tends to contract it.
We are then in the longest stage of the life of a star, the so-called main sequence. This supposes the 90%of his entire existence.
As the star depletes its reserve of hydrogen, it generates new chemical elements in its interior (carbon, neon and oxygen, among others).
The star ages and undergoes changes in its composition and size. Thus it becomes a dwarf, giant or supergiant star.
Its final outcome is also different, depending on the mass: the most massive stars will explode in the form of supernovas (leaving behind a neutron star or a black hole) while those of lower mass will become white dwarfs.
How was the star Eärendel detected?
Eärendel completed its stellar evolution and is therefore not in existence today.
But how has it been possible to detect an individual star so far from us and so close to the first moments of the universe?
To date, astronomical observations of such distant objects have corresponded to groups of stars (star clusters) embedded in the most primitive galaxies. That is, individual stars might not be distinguished at such enormous distances.
However, there is a possibility, as has been the case with Eärendel, that the light emitted by this very distant star will meet very massive objects (such as galaxy clusters) on its way to Earth.
As a consequence, the light from Eärendel has been amplified and distorted by these objects until finally being detected by the Hubble Space Telescope.
This phenomenon is called gravitational lens and it is an effect derived from the general theory of Einstein’s relativity. The equivalent process in optics would consist of the deformation of the image of an object when we look through a lens.
Eärendel has been observed thanks to the gravitational lens effect generated by the cluster of galaxies called WHL0137-08, located 5,500 light years from us, in addition to a suitable and fortunate alignment with Earth.
Why is discovery important?
The fact of having detected the light of such an old star unequivocally takes us back to the earliest moments of the Universe, when the primordial stars were made up of the simplest chemical elements such as hydrogen, helium and lithium.
Is regarding stellar populations of type III (very hot stars with practically no metals) of type II (with very low concentration of elements heavier than helium).
The discovery was made by the Hubble Space Telescope.
Eärendel is believed to be a Population II star.
It should be remembered that this discovery has been made by the ancient hubble space telescope Until now, such early stars had been individually invisible.
It will be its successor, the James Webb Space Telescope, that will allow us to look even further and earlier in the universe.
*Oscar del Barco Novillo is Associate Professor in the area of Optics at the University of Murcia. This note was published on The Conversation and is reproduced here under a Creative Commons license. click here to read the original version.
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