Observe stars with measles: they are extremely hot stars characterized by very bright spots, which cover about a quarter of their surface and are caused by magnetic fields. The discovery, published in the journal Nature Astronomy by the group coordinated by Yazan Al Momany, of the Astronomical Observatory of Padua of the National Institute of Astrophysics (INAF), was made thanks to the telescopes of the Southern European Observatory (Eso).
Many Italians are involved: from the INAF astronomical observatories of Padua, Abruzzo and Trieste, from the University of Padua and the National Institute of Nuclear Physics (INFN) of Pisa. This finding, the study authors explain, could help explain the origin of strong magnetic fields in many white dwarfs, objects that represent the final stage in the life of Sun-like stars.
Animation (source: Eso)
Measles stars are hidden inside globular clusters and are defined by astronomers as extreme stars of the horizontal branch. They have a mass of about half the Sun, but are four or five times warmer. They are also tormented by surface super-eruptions, millions of times more energetic than those of the Sun. Their white spots appear and disappear, while the stars rotate, causing regular changes in brightness.
These spots, explain the authors of the study, are different from the solar ones, which appear dark and about 3,000 times smaller. The explanation, the experts point out, is that they are brighter and warmer than the surrounding stellar surface, unlike the Sun where the spots appear darker because they are colder.
For Momany, “in our galaxy these hot and small stars are normally associated with the presence of a very close companion. They are special, because - he concluded - we know that they will skip one of the final stages of a star's life and die prematurely ".
