A Groundbreaking Discovery about Stars and Possibility of Life
Traditionally, it has been thought that the magnetic field surrounding stars slows down their rotation indefinitely. However, new observations suggest otherwise. As stars age, something unexpected happens: the potential for life increases.
This is viewed by researchers as a pivotal study, furthering our quest for habitable planets. The first planet outside our solar system, orbiting a sun-like star, 51 Pegasi, was discovered in 1995. Since then, more than 5500 exoplanets have been uncovered. However, an international team of astronomers revisited 51 Pegasi. They speculate that the present state of its magnetic field could be ideally suited for the evolution of complex life.
Harmful Radiation
Stars, similar to our sun, rapidly spin on their axis at birth. This creates a powerful magnetic field that can erupt intensely, bombarding surrounding planets with charged particles and harmful radiation. The star’s rotation slows over billions of years due to the weakening magnetic field created by stellar wind, a process known as magnetic braking. The slower rotation leads to a weaker magnetic field, which in turn leads to slower rotation, and so forth.
Until recently, astronomers believed that magnetic braking continued indefinitely, but new observations challenge this concept. “We are rewriting textbooks on how rotation and magnetism change in older stars, akin to the sun, midway through their lives,” says lead researcher Travis Metcalfe from Colorado. “Our findings have important implications for stars with planetary systems and their prospects for developing complex life.” A diminished magnetic brake also reduces the stellar wind, thereby decreasing the likelihood of destructive eruptions.
Building Evidence
Although the exoplanet that orbits 51 Pegasi does not move in front of its parent star from the Earth’s perspective, the star itself exhibits subtle differences in brightness. These were detected by European and American astronomers using new techniques. Consequently, they could make inferences about the star’s radius, mass, and age. More information about the star’s magnetic field was obtained because it leaves traces on the light the star emits. These measurements collectively allowed for an evaluation of the current magnetic field around the star.
The idea does not come entirely out of the blue. Previous observations from NASA’s Kepler Space Telescope already suggested that the magnetic brake may begin to weaken at the age of our sun. This was, however, indirect evidence. It was actually based on measurements of the rotation speeds of stars of different ages. It was clear that the slowing of the rotation halted around the age of the sun, after about 4.5 billion years.
Brake Ten Times Weaker
Only direct measurements of a star’s magnetic field can reveal underlying causes. In recent years, the magnetic field of multiple stars, including 51 Pegasi, was measured using the first-ever exoplanet. Gradually, a new understanding of how magnetism in stars changes as they age began to emerge. Most importantly, observations revealed that the magnetic brake abruptly changes in stars that are slightly younger than our sun. At this point, the brake becomes more than ten times weaker and continues to decline as the star ages.
Life on Land
But what triggers such a sudden change? It could be associated with an unexpected shift in the strength and complexity of the magnetic field and its impact on stellar wind. The newly discovered properties of 51 Pegasi show that – just like our sun – this star has already transitioned to the diminished magnetic braking phase. “It’s fantastic that we were able to reveal a new perspective on this planetary system, which plays such a crucial role in exoplanet astronomy,” says researcher Klaus Strassmeier. “This research is a significant step in the search for extraterrestrial life.”
In our solar system, the transition from underwater to land-based life occurred a few hundred million years ago. This coincided with the time when the magnetic braking of our sun began to decrease. Young stars bombard their planets with radiation inhibiting the development of complex life, but older stars provide a more stable environment. Therefore, astronomers suggest that the best place to search for extraterrestrial life would be around middle-aged or older stars.
