- Oscar del Barco Manzo
- The conversation*
image source, NASA, ESA, Brian Welch (JHU), Dan Coe (STScI)
Image of the galaxy that hosted the primordial star Eärendel.
Eärendel is the furthest 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 exists teach us about the life and death of its fellow men? And the Big Bang?
According to the calculations of the authors of this important discovery, published in the journal Nature, Eärendel it would have a mass 50 times that of the Sun and would have formed 900 million years after the Big Bang.
In fact, it assumes a small time with respect to the age of the universe, of about 13.800 million years.
This would imply that the light emitted by this very ancient star, collected by the Hubble Space Telescope, would have traveled for about 12.8 billion years.
image source, Getty Images
Eärendel would have formed 900 million years after the Big Bang.
Around that time Eärendel ceased to exist: it exploded at a time in the past, when it ran out of stellar fuel.
Before delving into the possible consequences of this discovery, we will examine some fundamental 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 hydrogen-rich galactic regions at very low temperatures) collapse due to their own gravitational pull, 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, as well as 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.
image source, Getty Images
We are therefore in the longest phase of a star’s life, the so-called main sequence. This supposes the 90%of his entire existence.
When the star runs out of its hydrogen supply, it generates new chemical elements within it (carbon, neon and oxygen, among others).
The star ages and undergoes changes in its composition and size. It thus becomes a dwarf, giant or supergiant star.
Its final result is also different, depending on the mass: the most massive stars will explode in the form of supernova (leaving behind a neutron star or a black hole) while they will become those of lower mass white dwarfs.
How was the star Eärendel detected?
Eärendel has completed its stellar evolution and therefore does not exist today.
But how was it possible to detect a single 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 could not be distinguished at such enormous distances.
However, the possibility exists, as in the case of Eärendel, that the light emitted by this very distant star will encounter very massive objects (such as clusters of galaxies) on its journey to Earth.
As a result, Eärendel’s light was amplified and distorted by these objects until it was finally 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 in the deformation of the image of an object when we look through a lens.
Eärendel was observed thanks to the gravitational lensing effect generated by the cluster of galaxies called WHL0137-08, located at 5,500 light years from us, as well as an appropriate and fortunate alignment with the Earth.
Why is the discovery important?
The fact of having detected the light of such an ancient star brings us unequivocally back to the first moments of the Universe, when the primordial stars were made up of the simplest chemical elements such as hydrogen, helium and lithium.
is approx type III stellar populations (very hot stars with practically no metals) type II (with very low concentration of elements heavier than helium).
image source, Getty Images
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 was made by the ancients Hubble Space Telescope Until now, these first stars had been individually invisible.
It will be its successor, the James Webb Space Telescope, which will allow us to look even further and earlier in the universe.
* Oscar del Barco Novillo is Associate Professor in the Optics sector at the University of Murcia. This note was published in The Conversation and is reproduced here under a Creative Commons license. click here to read the original version.
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