The Milky Way is our galactic home. It’s a barred spiral galaxy with a diameter between 150,000 and 200,000 light-years (ly).
It is estimated to contain 100–400 billion stars and more than 100 billion planets, which means that it is home to nearly innumerable solar systems.
As astronomers continue exploring our galactic neighborhood, they find, from time to time, things that challenge our very understanding of space.
One such discovery is a tiny, ancient star named J0023+0307.
It’s old, very old, located in the halo of our galaxy.
But it contains no detectable carbon, which is REALLY strange.
This image, taken with Hubble’s Advanced Camera for Surveys, shows a part the globular cluster NGC 6752. Behind the bright stars of the cluster, a denser collection of faint stars is visible — a previously unknown dwarf spheroidal galaxy. This galaxy, nicknamed Bedin 1, is about 30 million light-years from Earth. Image Credit: ESA/Hubble, NASA, Bedin, et al.
Now, they’ve uncovered another strange detail. The ancient star contains a massive amount of lithium.
That’s not too strange, it ut is unexpected of a star which is thought to have formed in the first 300 million years after the Big Bang, as the universes very first stars were beginning to die out.
Speaking about the mystery star, astronomer David Aguado of Cambridge University explains that “This primitive star surprises us for its high lithium content, and its possible relation to the primordial lithium formed in the Big Bang.”
As our universe came into existence, around 13.8 Billion years ago, only the lightest elements were formed. Elements like hydrogen, helium, lithium, and beryllium came into existence from neutrons, protons, electrons, positrons, photons, and neutrinos, something known as the Big Bang nucleosynthesis.
Then the big boys appeared. Heavier elements appeared created inside the first generations of stars. Eventually, the ancient stars died out and released their long-guarded secrets into the universe. Eventually, the elements that were released ended up being used in the formation of new stars across the universe.
And precisely that is how astronomers identify the oldest star’s in the universe, using something called spectroscopy. They look at stars, and if they don’t find a lot of heavier elements, that’s a sign that they formed during a time before these elements existed in the cosmos.
Curiously, J0023+0307 is less than a thousandth of the metallicity of the Sun, which means it is one of the most iron-poor stars we’ve ever discovered, and despite its mysterious absence of carbon, the star has lithium in nearly the same quantities as other Extremely-Metal-Poor Stars. Extremely metal-poor (EMP) stars are the living fossils with records of chemical enrichment history at the early epoch of galaxy formation.
“The lithium content of this primitive star is similar to that of other metal-poor stars in the halo of our galaxy, and they define, roughly, a constant value, independent of the value of the metal content of the star,” explained astronomer Jonay González Hernández of the Instituto de Astrofísica de Canarias in Spain.
Why is this important? Because in normal stars, at the temperature of just around 2.5 million Kelvin that is needed for a process called stellar hydrogen fusion, lithium ceases to exist as it is destroyed.
Some larger stars in the cosmos are able to keep some of their lithium in their cooler atmospheres, but astronomers argue that smaller stars don’t really have any lithium.
But…
Metal-poor-stars, just like J0023+0307, don’t burn at 2.5 million Kelvin, like stars that are rich in metals. This means that whatever their lithium content is, it most probably is the same one they had from the beginning.
This, in turn, means that J0023+0307 most likely contains lithium from the very Big Bang nucleosynthesis. That’s why studying this enigmatic star could help scientists understand what exactly happened in the universe when elements like hydrogen, helium, lithium, and beryllium came into existence during the Big Bang nucleosynthesis.