Huge magnetic spots may explain weird light patterns of super-hot stars

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Even stars aren’t immune to spotty conditions, new research suggests.

Scientists were studying a class of fairly small, unusually hot stars that have very little hydrogen. Astronomers are interested in studying these objects because when these stars run out of fuel, something strange happens: instead of turning into red giants as most smaller stars do, they become white dwarfs, a type of stellar remnant.

“These hot and small stars are special because we know they will bypass one of the final phases in the life of a typical star and will die prematurely,” Yazan Momany, lead author on the new research and an astronomer at the INAF Astronomical Observatory of Padua in Italy, said in a statement released by the European Southern Observatory, which runs the observatories used in this research.

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In particular, Momany and his colleagues focused on small hot stars found in dense clumps called globular clusters. In these neighborhoods, the scientists realized, the stars showed a weird pattern, with many of this class of star varying cyclically in brightness over time, dimming and brightening repeatedly.

The explanation they came up with relates to the magnetic fields of these stars, according to the researchers. “After eliminating all other scenarios, there was only one remaining possibility to explain their observed brightness variations,” Simone Zaggia, a study co-author from the INAF Astronomical Observatory of Padua in Italy, said in the statement. “These stars must be plagued by spots!”

That terminology might sound familiar: sunspots are patches on the surface of our sun caused by knots in the star’s magnetic field. But the researchers think something very different is happening on the stars they studied. On the sun, dark spots represent cool areas and are small and short-lived. On these distant stars, bright spots mark hot areas, and they can cover a quarter of the star and last for decades, according to the statement.

The scientists even caught a few of these stars shooting out massive flares — with ten million times the energy as flares produced by our sun, according to the researchers. And scientists believe this phenomenon is also tied to the stellar magnetic fields.

That makes this research intriguing for more than these specific observations and hypotheses, the scientists say. The findings also suggest that these magnetically rooted spots could be common to a wide range of stars, even those that look very different in other ways.

The research is described in an article published June 1 in the journal Nature Astronomy.

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