An international research team led by a researcher from the University of Vienna has successfully detected stellar winds from three Sun-like stars for the first time by recording the X-ray emission from their astrospheres, which are stellar analogues of the heliosphere surrounding our solar system. This groundbreaking study, published in Nature Astronomy, sheds light on the mass loss rate of these stars through their stellar winds, providing valuable insights into the evolution of both stars and planets. Understanding stellar winds is crucial in determining the fate of planetary atmospheres and their potential for habitability.
Stellar winds play a significant role in planetary evolution by driving processes that lead to atmospheric mass loss. While the escape rates of planets over short periods may seem negligible, they can have a cumulative effect over geological timescales, influencing whether a planet evolves into a habitable world or an airless rock. The composition of stellar winds, primarily made up of protons and electrons with small amounts of heavier ions, can be studied through the X-ray emission from astrospheres. Capturing electrons from neutral particles in the interstellar medium around the star, these ions emit X-rays that provide valuable information about the stellar winds.
The research team, led by Kristina Kislyakova, used observations from the XMM-Newton space telescope to detect X-ray emission from the astrospheres around three Sun-like main sequence stars: 70 Ophiuchi, epsilon Eridani, and 61 Cygni. By analyzing the spectral lines of oxygen ions, the researchers were able to estimate the total mass of stellar wind emitted by these stars and calculated their mass loss rates to be significantly higher than that of the Sun. This finding suggests that these stars exhibit stronger magnetic activity, leading to more intense stellar winds than our own star.
The study marks a significant milestone in the direct detection of stellar winds from Sun-like stars, which have historically been challenging to constrain. Previous attempts at measuring the strength of these winds relied on indirect evidence or upper limits based on secondary effects. By developing a new algorithm to disentangle the X-ray emissions from the astrospheres and the stars themselves, the researchers were able to detect X-ray charge exchange signals originating from stellar wind oxygen ions with unprecedented accuracy.
In the future, advancements in high-resolution instruments such as the X-IFU spectrometer of the European Athena mission will further enhance our ability to detect and study stellar winds in X-rays. This high spectral resolution instrument will provide detailed insights into the emission mechanisms of stellar winds, allowing researchers to distinguish between thermal emission from the stars and non-thermal charge exchange from the astrospheres. This direct detection method opens up new possibilities for studying the interactions between stellar winds and surrounding planets, offering a deeper understanding of the complex processes that shape planetary evolution in our galaxy.
