Extreme stellar flares have always captivated astronomers, but observing such phenomena on other stars had remained an elusive goal until now.
Thanks to the European Space Agency's XMM-Newton satellite, a team has made a breakthrough by detecting for the first time a coronal mass ejection coming from a red dwarf star. This discovery opens new perspectives on the violent behavior of stars.
An artist's impression of a large red star releasing a bright explosion. Swirling red and orange patterns surround the star, suggesting intense activity. In the background, a small blue planet with a wispy trail indicates its atmosphere is being blown away.
Credit: Olena Shmahalo/Callingham et al.
This coronal mass ejection stands out for its impressive density and speed, reaching 1,500 miles per second (2,400 kilometers per second). Such velocity, rare even for solar flares, possesses the energy needed to strip the atmosphere from planets orbiting nearby. The implications for extrasolar worlds are considerable, as this challenges their ability to maintain conditions suitable for life.
The detection was made possible by the LOFAR radio telescope, which picked up radio signals typical of shocks caused by coronal mass ejections. By combining this data with that from XMM-Newton, researchers were able to confirm the nature of the event and study the characteristics of the host star. This collaborative approach was essential for validating the observation.
The star in question, located about 130 light-years away, has a mass equivalent to half that of the Sun but rotates twenty times faster. Its magnetic field, three hundred times more powerful than that of our star, explains the intensity of the eruption. These extreme properties are common in red dwarfs, the most widespread stars in the galaxy.
This observation directly influences the definition of habitable planets, beyond simply being located in the temperate zone. Even a world positioned ideally can see its atmosphere destroyed by violent stellar flares, compromising any possibility of life. Habitability criteria must therefore incorporate the magnetic activity of stars.
The results of this study, published in
Nature, highlight the importance of space missions like XMM-Newton for exploring stellar phenomena. In the future, such discoveries could help refine the search for extraterrestrial life by identifying systems where planets have a chance of retaining their atmosphere despite the hostile environment.
Coronal mass ejections
Coronal mass ejections, or CMEs, are massive explosions of plasma and magnetic field from the stellar corona. They occur when magnetic energy accumulated on a star's surface is suddenly released, projecting charged particles into space. This phenomenon is well known for the Sun, where it can cause auroras on Earth, but it also affects other stars.
When a CME collides with a planet, it can interact with its atmosphere and magnetic field. If the planet doesn't have sufficient protection, the eruption can erode or even destroy its atmosphere, making the surface inhospitable. This explains why astronomers study these events to assess the habitability of exoplanets, particularly around active stars.
Detecting CMEs on other stars relies on advanced methods like radio astronomy, which captures waves emitted during shocks. These signals allow confirmation that material has left the star, without which the observation would remain indirect. Understanding these eruptions helps predict space conditions around distant stellar systems.
Research on extrasolar CMEs enriches our knowledge of space weather and its impact on life. By identifying the most turbulent stars, scientists can better target planets where environments are stable, thus accelerating the quest for biosignatures in the Universe.
The habitable zone of stars
The habitable zone, also called the Goldilocks zone, is the region around a star where temperatures allow water to remain in liquid state on a planet's surface. This condition is considered essential for the development of life as we know it. However, being positioned in this zone doesn't guarantee habitability, as other factors come into play.
Stellar activity, such as flares and solar winds, can seriously affect a planet's atmosphere. If the star frequently emits powerful CMEs, even a planet in the habitable zone can lose its atmosphere due to radiation and energetic particles. Thus, studying active stars, like red dwarfs, is crucial for assessing risks.
Red dwarfs, being the most common stars, host many potential exoplanets. Their longevity and small size make them attractive for the search for life, but their strong magnetic activity poses challenges. Recent observations show that their CMEs can be more intense than those of the Sun, reducing the chances of habitability for nearby planets.
To refine the search, astronomers combine data about the habitable zone with measurements of stellar activity. This allows for creating more accurate models to identify worlds where life could persist, taking into account not only the distance to the star, but also its erratic behavior and its impacts on the planetary environment.