Astrophysicists from the European Southern Observatory have discovered giant magnetic spots on the stars of the so-called horizontal branch of globular clusters - hot sub-dwarfs. This is reportedin the journal Nature Astronomy.
Using the powerful tools of the VLT telescope in Chile, scientists have studied the magnetic processes occurring on the surface of hot sub-dwarfs. Such space objects have variable brightness, while their mass is approximately half that of the sun, and the temperature is several times higher.
As Doctor of Physics and Mathematics, leading researcher at the Institute of Astronomy of the Russian Academy of Sciences Lev Rafailovich Yungelson, explained in an interview with RT, objects studied by European scientists from the point of view of the theory of star evolution are an intermediate link between red giants and white dwarfs.
“European colleagues have studied groups of stars of about 0.5 solar masses, which come from more massive stars - up to 7-8 solar masses. They are known as stars of the horizontal branch, or hot sub-dwarfs. These stars were previously red giants, but at the same time, for some reason, they lost their hydrogen shells and helium nuclei were exposed, ”said Jungelson.
Small and super-hot dwarf stars often form in binary systems, when a single star pulls the hydrogen envelope of its satellite by gravity. However, to the scientists ’surprise, most of the sub-dwarfs they studied, although they were in dense star clusters, did not have gravitationally bound satellites. Moreover, the brightness of such stars constantly and often changed, sometimes for several weeks or even days.
As a result, scientists came to the conclusion that hot sub-dwarfs are covered with massive spots caused by the powerful magnetic fields of these stars.
“When all other options were excluded, there was only one way to explain the observed changes in their brightness. These stars must have spots! ”Said one of the authors of the study from the Padua Observatory of the Italian National Institute of Astrophysics Simone Dzaja.
According to scientists, giant spots on hot dwarfs are very different from dark spots on our Sun, although they are also caused by magnetic fields. Unlike sunspots, these phenomena are very powerful and stable. At the same time, they are brighter and hotter than the surface of the sub-dwarf, so that they become not dark, but light. The researchers also recorded a series of sudden explosions - flashes of incredible power on the surface of such stars.
“They are akin to flares observed on our Sun, but ten million times more intense. Such dynamics, of course, is a surprise (for scientists. - RT ) and emphasizes the importance of magnetic fields to explain the properties of these stars, ”said another author of the study, Henry Boffin, astronomer at the European Southern Observatory in Germany.
Researchers believe that their discovery will help shed light on the origin of strong magnetic fields in stars at other evolutionary stages.
“In a broader context, a correlation is possible in the brightness of all hot stars: from young, similar to the Sun, to old stars of an extreme horizontal branch and dead white dwarfs. It is possible that all of these objects are affected by magnetic spots, ”concluded David Jones, co-author of the work and researcher at the Canary Institute of Astrophysics.