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Giant Magnetic Spots Discovered on the Surface of Extremely Hot Stars Hidden in Stellar Clusters - SciTechDaily
Jun 01, 2020 3 mins, 37 secs

Astronomers using ESO telescopes have discovered giant spots on the surface of extremely hot stars hidden in stellar clusters, called extreme horizontal branch stars.

Astronomers using European Southern Observatory (ESO) telescopes have discovered giant spots on the surface of extremely hot stars hidden in stellar clusters.

Not only are these stars plagued by magnetic spots, some also experience superflare events, explosions of energy several million times more energetic than similar eruptions on the Sun.

Astronomers using ESO telescopes have discovered giant spots on the surface of extremely hot stars hidden in stellar clusters.

The team, led by Yazan Momany from the INAF Astronomical Observatory of Padua in Italy, looked at a particular type of star known as extreme horizontal branch stars — objects with about half the mass of the Sun but four to five times hotter.

Surprisingly, however, the vast majority of these extreme horizontal branch stars, when observed in tightly packed stellar groups called globular clusters, do not appear to have companions.

When looking at three different globular clusters, Momany and his colleagues found that many of the extreme horizontal branch stars within them showed regular changes in their brightness over the course of just a few days to several weeks.

Spots on extreme horizontal branch stars (right) appear to be quite different from the dark sunspots on our own Sun (left), but both are caused by magnetic fields.

The spots on these hot, extreme stars are brighter and hotter than the surrounding stellar surface, unlike on the Sun where we see spots as dark stains on the solar surface that are cooler than their surroundings.

The spots on extreme horizontal branch stars are also significantly larger than sunspots, covering up to a quarter of the star’s surface.

While sunspots vary in size, a typical size is around an Earth-size planet, 3000 smaller than a giant spot on an extreme horizontal branch star.

Spots on extreme horizontal branch stars appear to be quite different from the dark sunspots on our own Sun, but both are caused by magnetic fields.

The spots on these hot, extreme stars are brighter and hotter than the surrounding stellar surface, unlike on the Sun where we see spots as dark stains on the solar surface that are cooler than their surroundings.

The spots on extreme horizontal branch stars are also significantly larger than sunspots, covering up to a quarter of the star’s surface.

As the hot stars rotate, the spots on the surface come and go, causing the visible changes in brightness.

Astronomers using ESO telescopes have discovered giant spots on the surface of extremely hot stars hidden in stellar clusters, called extreme horizontal branch stars.

Beyond the variations in brightness due to spots, the team also discovered a couple of extreme horizontal branch stars that showed superflares — sudden explosions of energy and another signpost of the presence of a magnetic field.

After six decades of trying to understand extreme horizontal branch stars, astronomers now have a more complete picture of them.

Moreover, this finding 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 and show similarities to extreme horizontal branch stars.

“The bigger picture though,” says team member, David Jones, a former ESO Fellow now at the Instituto de Astrofísica de Canarias, Spain, “is that changes in brightness of all hot stars — from young Sun-like stars to old extreme horizontal branch stars and long-dead white dwarfs — could all be connected.

Spots on extreme horizontal branch stars (right) appear to be quite different from the dark sunspots on our own Sun (left), but both are caused by magnetic fields.

The spots on these hot, extreme stars are brighter and hotter than the surrounding stellar surface, unlike on the Sun where we see spots as dark stains on the solar surface that are cooler than their surroundings.

The spots on extreme horizontal branch stars are also significantly larger than sunspots, covering up to a quarter of the star’s surface.

While sunspots vary in size, a typical size is around an Earth-size planet, 3000 smaller than a giant spot on an extreme horizontal branch star.

Reference: “A plague of magnetic spots among the hot stars of globular clusters” 1 June 2020, Nature Astronomy.

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