Astronomers have found the "cleanest" star in the universe

This makes it one of the oldest and least altered objects in the Universe that has retained its pristine chemical composition.

The discovery was made by a team of scientists led by Alexander Ji from the University of Chicago. The results are posted on the arXiv preprint server and will soon be presented in scientific journals.

The object has been labelled SDSS J0715-7334. It is a red giant located in the halo of the Milky Way, and the authors estimate that it contains fewer heavy elements than any other known star.

Its metallicity, denoted as Z (the fraction of elements heavier than helium), is less than 7.8 × 10-⁷. By comparison, the previous record holder, the star J1029+1729, had a Z ≈ 1.4 × 10-⁶. This means that the new find is more than twice as "pure" in composition.

"It is more than ten times poorer in iron than the previously discovered SMSS J0313-6708, which was previously thought to be the poorest iron-poor star," the study authors said.

Stars are formed from gas containing hydrogen, helium and (in later epochs) heavy elements. The less metals - the more ancient the star. Scientists suggest that SDSS J0715-7334 was formed from matter ejected into space as a result of the explosion of the star Population III - the first objects that appeared shortly after the Big Bang.

The peculiarity of the star is that even the carbon content, which is usually preserved in such stars, is extremely low here. This makes it particularly rare and valuable from the point of view of studying the processes of the early Universe.

According to an orbital analysis using data from the Gaia space telescope, the star was originally part of the Large Magellanic Cloud, a satellite galaxy of the Milky Way. It later migrated into our galaxy.

SDSS J0715-7334 also helps explain how stars can form at such low metallicity. Scientists note that such stars could not have formed without the help of cosmic dust, which plays a key role in cooling gas clouds. This supports the hypothesis of the importance of "dust cooling" in the early Universe.