The Huge Bang primarily created two parts: hydrogen and helium. It additionally produced tiny traces of lithium and some different gentle isotopes, however to start with there was hydrogen and helium. All the opposite, heavier parts shaped later, both within the cores of stars, by way of stellar collisions, or different astrophysical processes. Even now hydrogen and helium make up a lot of the fabric world that astronomers refer to all other elements as metals. Mud within the wind, you may say.
One consequence of that is you can get a reasonably good concept of a star’s age by the quantity of metals seen in its spectrum. The very first stars, the progenitors of all others, would simply comprise hydrogen and helium. The gasoline mud solid off by their demise would comprise some metals, and so would the second technology of stars. With every technology a bit extra metallic is added to the combo, so the higher the metallicity of a star, the youthful it usually is. Our Solar is barely 5 billion years outdated, for instance, and it has a excessive metallicity.
The primary stars have possible long-vanished from the cosmos. With solely hydrogen and helium to work with, they might have wanted tons of of photo voltaic plenty to set off nuclear fusion of their core, and they might have change into supernovae in a cosmic blink. To check these grandmother stars, astronomers have principally appeared for galaxies on the farthest fringe of the observable universe. Galaxies with unusually low metallicity. However one other method is to search for historic stars in our galactic neighborhood. The concept is that the primary stars could have given rise to some second-generation stars with low plenty. If these stars had been smaller than the Solar, they might reside lengthy sufficient to nonetheless be round at present. Just lately astronomers have discovered simply such a star.
*A log graph plotting low metallicity stars by their carbon abundance vs their iron abundance. SDSS J0715-7334 is seen to have the bottom of each. Credit score: Ji, et al*
The star is named SDSS J0715-7334. It’s a pink big star within the halo of the Massive Magellanic Cloud. The metallicity of this star is so low that even essentially the most distant, most primordial galaxies we have noticed have ten occasions the metallicity of this star. SDSS J0715-7334 is the closest factor we have discovered to a pristine, metal-free star. Its metallic abundances inform us just a few fascinating issues about early star formation.
To start with, by wanting on the particular abundances of parts corresponding to carbon, magnesium, and iron relative to hydrogen, we are able to get a deal with on the dimensions of its father or mother star. If SDSS J0715-7334 is a second-generation star, then it shaped inside the supernova remnant of a 30 solar-mass star, which is surprisingly small. One other fascinating facet of the star is that its abundance of carbon is exceptionally low. That is stunning as a result of giant stars are environment friendly producers of carbon, nitrogen, and oxygen because of the helium burning CNO fusion cycle. The shortage of carbon means that there was loads of cooled mud within the star-forming area, which is important for small early stars to type. Lastly, the movement of SDSS J0715-7334 inside the Massive Magellanic Cloud means that it shaped inside the small galaxy’s halo and isn’t merely a passing customer. Which means that we’re more likely to discover extra of those stars in our galactic neighborhood, which suggests we can evaluate observations of distant galaxies to these of native pristine stars.
Reference: Ji, Alexander P., et al. “A nearly pristine star from the Large Magellanic Cloud.” *arXiv preprint* arXiv:2509.21643 (2025).
