Giant Magnetic Spots Discovered on the Surface of Extremely Hot Stars Hidden in Stellar Clusters

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Star Plagued by Giant Magnetic Spot

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Astronomers utilizing ESO telescopes have actually found huge areas on the surface area of exceptionally hot stars concealed in excellent clusters, called severe horizontal branch stars. This image reveals an artist’s impression of what among these stars, and its huge whitish area, may appear like. The area is intense, uses up a quarter of the star’s surface area and is triggered by electromagnetic fields. As the star turns, the area on its surface area reoccurs, triggering noticeable modifications in brightness. Credit: ESO/L. Calçada, INAF-Padua/S. Zaggia

Astronomers utilizing European Southern Observatory (ESO) telescopes have actually found huge areas on the surface area of exceptionally hot stars concealed in excellent clusters. Not just are these stars pestered by magnetic areas, some likewise experience superflare occasions, surges of energy numerous million times more energetic than comparable eruptions on the Sun. The findings, released today in Nature Astronomy, aid astronomers much better comprehend these confusing stars and open doors to fixing other evasive secrets of excellent astronomy.


Astronomers utilizing ESO telescopes have actually found huge areas on the surface area of exceptionally hot stars concealed in excellent clusters. This video provides a summary of the discovery. Credit: ESO

The group, led by Yazan Momany from the INAF Astronomical Observatory of Padua in Italy, took a look at a specific kind of star called severe horizontal branch stars — things with about half the mass of the Sun however 4 to 5 times hotter. “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,” states Momany, who was formerly a personnel astronomer at ESO’s Paranal Observatory in Chile. “In our Galaxy, these peculiar hot objects are generally associated with the presence of a close companion star.”

Surprisingly, nevertheless, the large bulk of these severe horizontal branch stars, when observed in securely loaded excellent groups called globular clusters, do not appear to have buddies. The group’s long-lasting tracking of these stars, made with ESO telescopes, likewise exposed that there was something more to these strange things. When taking a look at 3 various globular clusters, Momany and his associates discovered that a lot of the severe horizontal branch stars within them revealed routine modifications in their brightness throughout simply a couple of days to numerous weeks.

Spots on the Sun vs Spots on Extreme Horizontal Branch Stars

Spots on severe horizontal branch stars (right) seem rather various from the dark sunspots on our own Sun (left), however both are triggered by electromagnetic fields. The areas on these hot, severe stars are brighter and hotter than the surrounding excellent surface area, unlike on the Sun where we see areas as dark discolorations on the solar surface area that are cooler than their environments. The areas on severe horizontal branch stars are likewise substantially bigger than sunspots, concealing to a quarter of the star’s surface area. While sunspots differ in size, a common size is around an Earth-size world, 3000 smaller sized than a huge area on a severe horizontal branch star. Credit: ESO/L. Calçada, INAF-Padua/S. Zaggia

“After eliminating all other scenarios, there was only one remaining possibility to explain their observed brightness variations,” concludes Simone Zaggia, a research study co-author from the INAF Astronomical Observatory of Padua in Italy and a previous ESO Fellow: “these stars must be plagued by spots!”

Spots on severe horizontal branch stars seem rather various from the dark sunspots on our own Sun, however both are triggered by electromagnetic fields. The areas on these hot, severe stars are brighter and hotter than the surrounding excellent surface area, unlike on the Sun where we see areas as dark discolorations on the solar surface area that are cooler than their environments. The areas on severe horizontal branch stars are likewise substantially bigger than sunspots, concealing to a quarter of the star’s surface area. These areas are extremely relentless, lasting for years, while private sunspots are momentary, lasting just a few days to months. As the hot stars turn, the areas on the surface area reoccured, triggering the noticeable modifications in brightness.


Astronomers utilizing ESO telescopes have actually found huge areas on the surface area of exceptionally hot stars concealed in excellent clusters, called severe horizontal branch stars. This animation reveals what among these stars, and its huge whitish area, may appear like. The area is intense, uses up a quarter of the star’s surface area and is triggered by electromagnetic fields. As the star turns, the area on its surface area reoccurs, triggering noticeable modifications in brightness. Note that the motion does not represent the rotation of the star: it imitates the motion of a cam observing the star up close. Credit: ESO/L. Calçada, INAF-Padua/S. Zaggia

Beyond the variations in brightness due to areas, the group likewise found a number of severe horizontal branch stars that revealed superflares — unexpected surges of energy and another signpost of the existence of an electromagnetic field. “They are similar to the flares we see on our own Sun, but ten million times more energetic,” states research study co-author Henri Boffin, an astronomer at ESO’s head office in Germany. “Such behavior was certainly not expected and highlights the importance of magnetic fields in explaining the properties of these stars.”

After 6 years of attempting to comprehend severe horizontal branch stars, astronomers now have a more total image of them. Moreover, this finding might assist discuss the origin of strong electromagnetic fields in numerous white overshadows, things that represent the last in the life of Sun-like stars and reveal resemblances to severe horizontal branch stars. “The bigger picture though,” states employee, David Jones, a previous 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. These objects can thus be understood as collectively suffering from magnetic spots on their surfaces.”


Spots on severe horizontal branch stars (right) seem rather various from the dark sunspots on our own Sun (left), however both are triggered by electromagnetic fields. The areas on these hot, severe stars are brighter and hotter than the surrounding excellent surface area, unlike on the Sun where we see areas as dark discolorations on the solar surface area that are cooler than their environments. The areas on severe horizontal branch stars are likewise substantially bigger than sunspots, concealing to a quarter of the star’s surface area. While sunspots differ in size, a common size is around an Earth-size world, 3000 smaller sized than a huge area on a severe horizontal branch star. Credit: ESO/L. Calçada, INAF-Padua/S. Zaggia

To get to this outcome, the astronomers utilized numerous instruments on ESO’s Very Large Telescope (VLT), consisting of VIMOS, FLAMES and FORS2, along with OmegaCAM connected to the VLT Survey Telescope at Paranal Observatory. They likewise used ULTRACAM on the New Technology Telescope at ESO’s La Silla Observatory, likewise in Chile. The development came as the group observed the stars in the near-ultraviolet part of the spectrum, permitting them to expose the hotter, severe stars sticking out intense among the cooler stars in globular clusters.

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Reference: “A plague of magnetic spots among the hot stars of globular clusters” 1 June 2020, Nature Astronomy.
DOI: 10.1038/s41550-020-1113-4

The group is made up of Y. Momany (INAF Astronomical Observatory of Padua, Italy [INAF Padua]), S. Zaggia (INAF Padua), M. Montalto (Department of Physics and Astronomy, University of Padua, Italy [U. Padua]), D. Jones (Instituto de Astrofísica de Canarias and Department of Astrophysics, University of La Laguna, Tenerife, Spain), H.M.J. Boffin (European Southern Observatory, Garching, Germany, S. Cassisi (INAF Astronomical Observatory of Abruzzo and INFN Pisa, Italy), C. Moni Bidin (Instituto de Astronomia, Universidad Catolica del Norte, Antofagasta, Chile), M. Gullieuszik (INAF Padua), I. Saviane (European Southern Observatory, Santiago, Chile), L. Monaco (Departamento de Ciencias Fisicas, Universidad Andreas Bello, Santiago, Chile), E. Mason (INAF Astronomical Observatory of Trieste, Italy), L. Girardi (INAF Padua), V. D’Orazi (INAF Padua), G. Piotto (U. Padua), A.P. Milone (U. Padua), H. Lala (U. Padua), P.B. Stetson (Herzberg Astronomy and Astrophysics, National Research Council, Victoria, Canada), and Y. Beletsky (Las Campanas Observatory, Carnegie Institution of Washington, La Serena, Chile).