The exceptional star is the most virgin object known in the universe

A relatively nearby star which seems to be lacking in almost all the heavy elements produced by the supernovae could be a direct descendant of the very first stars that have formed in the universe.

Astronomers believe that the first stars were only composed of hydrogen and helium that floated after the Big Bang. It was only when these stars lacked fuel and exploded in a supernova that the heavier elements that helium have spread. The remains of gas rich in element of these initial explosions then formed the next generation of stars, the cycle repeating to possibly produce all the elements that we see in the stars and the planets today.

Most of the stars we see in our galaxy are many generations withdrawn from this initial population of stars, but some astronomers nicknamed “stellar archaeologists” have found almost virgin stars. It is believed that these are stars of the “second generation”, born from the remains of the very first stars.

Now, Alexander Ji at the University of Chicago and his colleagues has found a star that has the lowest quantity of “metals” – which for astronomers means all the elements other than hydrogen or helium – in the known universe. The star, called SDSS J0715-7334, is located in the large Magellanic cloud, a satellite galaxy of the Milky Way, and has a metal content of about 0.8 parts per million, or about 20,000 times less than our sun.

After first spotting the star in the data of the Sloan Digital Sky survey because of its unusually weak metallicity, JI and his colleagues then observed it with the Magellan Telescope of the Las Campanas Observatory in Chile. They found that the star contains extremely low quantities of iron, comparable to those observed in other almost virgin stars. However, they found that he also had extremely low quantities of carbon, at levels that we do not see in the stars of the Milky Way.

“It is a pretty cool discovery, but [in terms of iron levels] It’s just a little more extreme than some other examples that we have already found, “said Anke Ardern-Arenten at the University of Cambridge.” But what is particularly interesting is that most [nearly] The virgin stars that we know have a lot of carbon, when it does not. »»

This could suggest that it was formed in a fairly different way from the almost impartial stars that we see in the Milky Way, explains Anna Frebel at the Massachusetts Institute of Technology.

To make a star the size of SDSS J0715-7334, you need a relatively small and fresh gas tuft, which generally requires heavier elements with high energy electrons, such as carbon, so that gas can lose enough energy. But the virtual absence of carbon in the star would make cooling like that difficult.

One of the only alternative explanations is that there was in place a cloud of cosmic dust, made up of heavier elements, which helped him to cool, a mechanism that we do not see so early in the history of the universe, at least in our own galaxy.

“The question arises, different environments in different places in the universe cool their gas differently at first?” said Frebel. “We can ask the question, why do they cool it differently, but I don’t think we have a good answer to that.”

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