Infrared image of the shock wave (red arc) created by the enormous giant star Zeta Ophiuchi in an interstellar dust cloud – NASA/JPL-CALTECH
April 12 () –
An international team led by a researcher from the University of Vienna has been detected for the first time directly stellar winds from three Sun-like stars.
The observation was produced by recording X-ray emission from their astrospheres and has placed constraints on the rate of mass loss from stars through their stellar winds.
Astrospheres, stellar analogues of the heliosphere surrounding our solar system, are very hot bubbles of plasma propelled by stellar winds into the interstellar medium, a space full of gas and dust.
Studying the stellar winds of low-mass, Sun-like stars allows us to understand stellar and planetary evolution and, ultimately, the history and future of our own star and solar system. Stellar winds drive many processes that evaporate planetary atmospheres into space and, therefore, lead to loss of atmospheric mass.
Although the escape rates of planets over an hour or even a year are small, they operate over long geological periods. Losses accumulate and can be a decisive factor for a planet to evolve into a habitable world or an airless rock.
Despite their importance to the evolution of both stars and planets, winds from Sun-like stars are very difficult to limit. Composed primarily of protons and electrons, they also contain a small amount of heavier, highly charged ions (e.g., oxygen, carbon). It is these ions that, by capturing electrons from the neutrals of the interstellar medium around the star, emit X-rays.
The team led by Kristina Kislyakova, senior scientist at the Department of Astrophysics at the University of Vienna, has for the first time detected X-ray emission from astrospheres around three Sun-like stars, so-called main sequence stars, which are stars in the prime of its life and has therefore recorded these winds directly for the first time, allowing them to impose constraints on the rate of mass loss from stars through their stellar winds.
These results, based on observations made with the XMM-Newton space telescope, are currently published in Nature Astronomy. The researchers observed the spectral signatures (so-called spectral lines) of oxygen ions with XMM-Newton and were able to determine the amount of oxygen and, ultimately, the total mass of the stellar wind emitted by the stars.
For the three stars with detected astrospheres, named 70 Ophiuchi, epsilon Eridani and 61 Cygni, the researchers estimated their mass loss rates to be 66.5 +/- 11.1, 15.6 +/- 4.4 and 9 .6 +/- 4.1 times the solar mass loss rate, respectively. This means that the winds from these stars are much stronger than the solar wind, which could be explained by the greater magnetic activity of these stars.
“In the solar system, charge exchange emission from the solar wind has been observed from planets, comets, and the heliosphere and provides a natural laboratory to study the composition of the solar wind“explains the lead author of the study, Kislyakova.
“Observing this emission from distant stars is much more complicated due to the weakness of the signal. Furthermore, the distance to the stars makes it very difficult to differentiate the signal emitted by the astrosphere from the actual X-ray emission from the star.” own star, part of which is “spread” over the telescope's field of view due to instrumental effects.
“We have developed a new algorithm to divert stellar and astrospheric contributions to the emission and have detected charge exchange signals originating from oxygen ions in the stellar wind and the surrounding neutral interstellar medium of three main sequence stars.
“This was the first time that X-ray charge exchange emission has been detected from astrospheres of this type of star. Our estimated mass loss rates can be used as a reference point for stellar wind models. and expand our limited observational evidence for winds from sun-like stars.”
Co-author Manuel Güdel, also from the University of Vienna, adds: “For three decades, efforts have been made around the world to test the presence of winds around Sun-like stars and measure their strength, but so far there is only indirect evidence based on its side effects.” The effects on the star or its environment allude to the existence of such winds; Our group previously attempted to detect the intensity of radio emission from winds, but could only place upper limits on the winds without detecting the winds themselves.
“Our new X-ray-based results pave the way to finding and even imaging these winds directly and studying their interactions with surrounding planets.”
