Stellar wind from three Sun-like stars recorded for the first time

Astrophysicists have been able to calculate the mass loss of stars through stellar winds

An international team of researchers led by astrophysicist Kristina Kislyakova from the University of Vienna was able to directly detect the stellar winds of three Sun-like stars for the first time: by recording the X-ray emission from the celestial regions of these stars, their mass loss through the stellar wind could be determined. A stellar wind blowing on the studied stars is 10 to 66 times stronger than that of our Solar System. The present study was carried out in Natural Astronomy Published.

Just as the heliosphere surrounds our solar system, other stars are also surrounded by an astrosphere—imagined as a kind of bubble of hot plasma blown by the interstellar wind through interstellar space filled with gas and dust. These stellar winds drive many processes that are central to understanding stellar and planetary evolution in these star systems, such as the evaporation of planetary atmospheres and associated mass loss. Although this loss of mass from planetary atmospheres is small per year, over long geologic timescales these losses are a decisive factor in whether a planet evolves into a habitable world or airless rock.

However, so far there is only indirect evidence for the presence of these stellar winds in Sun-like stars (so-called main-sequence stars, i.e. stars at the prime of their lives). An international research team led by Kristina Kislyakova, senior scientist at the University of Vienna's Institute of Astrophysics, has now succeeded for the first time in directly detecting the stellar winds of three Sun-like stars and measuring their stellar mass loss. The reason

To do this, the team used X-ray emission: the stellar wind consists mainly of protons and electrons, but also small amounts of heavier, more charged ions (e.g. oxygen, carbon). These ions emit X-rays by capturing electrons from the neutral interstellar medium surrounding the star.

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Manuel Gudel, head of the “Star and Planet Formation” research group at the Institute of Astrophysics at the University of Vienna, highlighted the team's progress: “For three decades, many groups around the world have been trying to detect winds. Measure their strength around stars like the Sun, but “so far, they have not been able to detect winds in the star or its surroundings. There is only indirect evidence for the existence of such winds, based on secondary effects.” His research team had previously attempted to record radio emissions from the wind, but were only able to provide upper limits on the strength of the wind, but they were unable to detect the wind. “Our new X-ray-based results now point to these winds directly. “pave the way to discover and image and study their interactions with surrounding planets,” Goodell said.

X-ray emission from the astrosphere is detected

Using observations with the XMM-Newton Space Telescope, the team succeeded for the first time in directly detecting this X-ray emission from the celestial regions of Sun-like stars and separating it from the X-ray emission of stars. This made it possible to directly record the interstellar wind for the first time and calculate the mass loss rate of stars through the interstellar wind.

By analyzing the spectral fingerprints (called spectral lines) of the oxygen ions, the researchers determined the amount of oxygen and ultimately the total mass of the stellar wind emitted by the stars. For the stars studied (70 Ophiuchi, epsilon Eridani and 61 Cygni) it was shown that the stellar wind is significantly stronger: in the case of the star 70 Ophiuchi the mass loss rate is 66.5 ± 11.1 times higher. The stars Epsilon Eridani and 61 Signi have an estimated mass loss rate of 15.6±4.4 and 9.6±4.1 times that of our Sun, respectively. The strong magnetic activity of these stars may explain the strong winds.

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The Solar System as a Natural Laboratory

“Within our solar system, the emission of grounding transfer has already been observed in planets, comets and the heliosphere – so here we have a natural laboratory to study the composition of the solar wind,” explains the present lead author. Newspaper Natural Astronomy Published study, Kristina Kislyakova. Observing this emission from distant stars is more difficult because of the signal's weakness: “Furthermore, due to the distance to the stars, it is more complicated to separate the astrosphere emission signal from the true X-ray emission of the star, some of this emission being 'scattered' into the telescope's field of view due to instrumental effects. The X of the star We developed a new method for separating -ray emissions from the celestial sphere. We were able to identify charge transfer signals from oxygen “ions originating from the stellar wind and the neutral interstellar medium of three main-sequence stars.” The estimated mass-loss rates will serve as a benchmark for future stellar wind models and Sun-like stars. The observational data previously defined for wind can be expanded.

Figure 1: Infrared image of a shock wave (red arc) created by the massive giant star Zeta Ophiuchi in a cloud of interstellar dust. Weak winds of Sun-like main-sequence stars are more difficult to observe C: NASA/JPL-Caltech; NASA and The Hubble Heritage Team (STScI/AURA); Credit: CR O'Dell, Vanderbilt University

Figure 2: XMM-Newton X-ray image of the star 70 Ophiuchi (left) and X-ray emission of the region around the star (the “annulus”), shown in the spectrum of the energy of the X-ray photons (right). Most of the emission consists of X-ray photons originating from the star itself, but scattered within the observing telescope and across the camera (approximated by the model shown with the blue line), but there is a significant contribution around the oxygen K-alpha line. energy of 0.56 keV, which comes from the extended astrosphere and not from the star itself (this contribution is included in the red model) C: Kislyakova et al. Nature Astronomy, 10.1038/s41550-024-02222-x, 2024

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Read more about space exploration at the University of Vienna Article Europe in the Space Race in the scientific journal Rudolphina at the University of Vienna or in the general section Nature, Climate and Cosmos.

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