Science. New development in the blue star sequence – Publimetro México

Madrid, 25 (European press)

Some humans try to appear younger than they really are; The stars do, too, concluded an international team of astronomers in a research paper published in Nature Astronomy.

They suggest that stars in star clusters gain mass in two different ways: through “normal” disk accretion, which causes rapid rotation and contributes to the red main sequence, or through binary star mergers, which causes slowly spinning stars that appear bluer and darker , and therefore younger.

It all began with probably the most famous diagram in astronomy, the Herzsprung-Russell diagram. Created independently by two astronomers, Eignar Hertzbrung and Henry Norris Russell over a century ago, this chart arranges stars according to their brightness and color. Much of what we know about stars and their evolution comes from studying how the stars are grouped in this diagram. Our sun, for example, is still on the so-called “main sequence”, where most of the stars are.

However, some stars are located in strange positions in this chart. For a long time, it was difficult to clearly distinguish between different groups, because conventional telescopes are not accurate enough. However, recent Hubble Space Telescope observations have revealed that the main sequences of young, young star clusters consist of several separate components. In particular, data for NGC 1755, an open star cluster in the Large Magellanic Cloud about 60 million years old, showed many puzzling features, such as the double main sequence.

“We think that stars in star clusters were born at the same time from the same gas cloud,” explains Chen Wang, who received a PhD from the University of Bonn and recently became a post-doctoral researcher at MPA. astronomy) is the lead author of the study. They should have the same age and the same chemical composition. But if this is true, how can there be a whole second string of stars that are bluer?

This strange feature has left astronomers confused. Many even ignored this feature, since it was difficult to find an explanation. However, with her background as a theoretical astrophysicist, Chen combined clues to suggest the origin of these blue major sequence stars.

First, using computer simulations, he showed that blue stars could be explained if they were rotating more slowly than other stars in the cluster. Second, recent models of merging stars have shown that merging stars become extremely magnetic and rotate very slowly. Qin combined these two ideas and suggested that blue stars are actually stars that rotate very slowly as a result of stellar mergers.

“The life of stars in binary systems can be very complex and different from the lives of individual stars,” he says. “Through our computer simulations, we can study the effect of stellar mergers on the colors and luminosity of stars and simulate features on the Hertzsprung-Russell diagram.”

Binary fusion creates a star more massive than any of its parent stars, with a higher basic hydrogen content than a single star of equal age of the same mass. Therefore, the fusion products may be the same age as all the other stars in the cluster, but appear younger on the color volume chart, indicated by their blue color. Also, the mass distribution of main sequence stars in blue and red is different, which can naturally be explained by the origin of the merger.

“The merger hypothesis that Chen put forward as an explanation for main sequence blue stars is very tempting because it provides a logical way to combine the various mysteries,” says Selma de Mink, director and chair of the Stellar Astronomy Group at MPA. This means that a significant portion of the stars dissolve with a companion before their entire lives begin. If Qin is right, and he probably is, this sheds new light on many questions about how stars form, why they sometimes spin fast and sometimes slow, and why some have magnetic fields.

In the Nature Astronomy paper, we show that it can be inferred from star cluster data that stars can form in two different ways: by gas accretion (as has always been thought) or by stellar fusion (which is new and includes about 30 percent), says Professor Norbert Langer of The Argelander Institute for Astronomy at the University of Bonn and the Max Planck Institute for Radio Astronomy in Bonn “All Stars)”. “This sheds new light on the function of the elementary mass of stars, as well as on the bimodal distribution of their rotations and magnetic fields.”

And so, more than a century after Hertzsprung and Russell drew up their famous scheme, the explanation for the mysterious mystery of the blue sequence may finally be found. But of course, as with any hypothesis, this will need further testing.