Strange spots and powerful flashes discovered on incredibly hot stars

US, WASHINGTON (ORDO NEWS) — Astronomers have discovered on stars of an exotic and mysterious type spots that have lived for decades, and flashes are millions of times more powerful than solar ones.

The achievement is described in a scientific article published in the journal Nature Astronomy.

The stars of the extreme horizontal branch of the Hertzsprung-Russell diagram , or KGV stars, have been haunting scientists for six decades. Experts are trying to understand why these objects, being half the size of the Sun, have a colossal temperature of 20-30 thousand degrees.

Such luminaries have already run out of hydrogen in the core and even passed the stage of the red giant . At this stage of evolution, all the stars become hotter, but the KGV stars are just anomalously red-hot. There are many hypotheses trying to explain the nature of this phenomenon, but not one of them has yet been confirmed.

Gathering information about these mysterious celestial bodies, researchers for several years observed KGV stars in three globular clusters. The observations were carried out in the optical and near ultraviolet range using the world’s largest telescope VLT.

Scientists have discovered something strange. Many KGV stars regularly changed their brightness with a frequency from several days to several weeks.

“After all the other scenarios were eliminated, there was only one opportunity to explain the observed brightness variability,” says co-author Simone Zaggia of the National Institute of Astrophysics in Italy. “These stars should be spotted!”

The rotation of the “spotted” star around its axis leads to the fact that areas of different brightness fall into the field of view of the telescope, hence periodic changes in brightness.

However, these spots are very different from the sun.

Firstly, these are light spots against a relatively dark background, and not vice versa. They are brighter than the rest of the surface of the sun, in contrast to sunspots, which are darker than the surrounding surface of the Sun.

Secondly, spots on KGV stars are thousands of times larger than spots on the Sun: one spot can occupy up to a quarter of the entire surface of a star.

Thirdly, these spots are so stable that they seem to exist for decades (while the lifetime of a single sunspot is measured in days or months).

In addition, unusually powerful flares were discovered in the two studied stars.

“They look like flashes that we see on the Sun, but ten million times more powerful,” explains co-author Henri Boffin from the headquarters of the European Southern Observatory. “We did not expect such behavior in these stars. It testifies how important it is to take magnetic fields into account when explaining their properties.”

Let us explain that all manifestations of the activity of stars, including spots and flares, are associated with the restructuring of powerful magnetic fields in the upper layers of these celestial bodies.

This is not the first observation of spots on the surface of another star. But it shows that spots may be more common than astronomers thought. In particular, even white dwarfs , which also have a powerful magnetic field, can be “tarnished” (and showing changes in brightness in this connection) .

“The main thing is that the brightness changes of all hot stars, from young stars like the Sun to old stars of the extreme horizontal branch and long-dead” white dwarfs, can now be connected to each other. All these objects can have magnetic spots on the surface, “the co-author summarizes research David Jones ( by David Jones ) of the Canary Islands Institute of astrophysics in Spain.

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