Once upon a time in spacetime, scientists proposed that stars exerted an infinite magnetic brake, causing their rotation to slow down forever. With new observations and advanced techniques, they now investigated the magnetic secrets of the star and discovered that they were not what they expected. Cosmic hotspots to search for alien neighbors may be around stars going through midlife crises or even later in life.

This groundbreaking work sheds light on magnetic phenomena and habitable environments. Astrophysics Journal Letters.

In 1995, Swiss astronomers Michael Major and Didier Queloz announced the first discovery of a planet outside our solar system orbiting a distant, sun-like star known as 51 Pegasus. More than 5,500 so-called exoplanets have since been found orbiting other stars in our galaxy, and in 2019 two scientists shared the Nobel Prize in Physics for their groundbreaking work. This week an international team of astronomers published new observations of 51 Pegasi; This suggested that the current magnetic environment around the star may be particularly suitable for the development of complex life.

Stars like the Sun are born in a rapid rotation that creates a powerful magnetic field that can explode violently, bombarding planetary systems with charged particles and harmful radiation. Over billions of years, the star’s rotation gradually slows as its magnetic field is pulled away by the wind flowing across its surface, a process known as magnetic braking. Slower rotation creates a weaker magnetic field, and the two properties continue to decay together, feeding off each other.

Until recently, astronomers assumed that magnetic braking lasted indefinitely, but new observations have begun to question this assumption.

“We are rewriting the textbooks on how spin and magnetism in old stars like the Sun change after their middle ages,” says team leader Travis Metcalf, a senior scientist at the White Dwarf Probe in Golden, Colorado, USA. “Our results will have important implications for stars with planetary systems and their prospects for the development of advanced civilizations.”

“This is because the weakened magnetic braking also dampens the stellar wind, reducing the likelihood of catastrophic explosions,” adds Klaus Strassmeier, director of the Leibniz Institute for Astrophysics in Potsdam, Germany, and a co-author of the study.

A team of United States and European astronomers used the Potsdam Echelle Polarimetric and Spectroscopic System to compare observations of 51 Pegasus from NASA’s Transiting Exoplanet Survey Satellite (TESS) with magnetic field data taken from the Large Binocular Telescope (LBT) in Arizona. combined with advanced measurements of the field. Vehicle (PEPSI).

Although the exoplanet orbiting 51 Pegasus does not pass in front of its parent star as seen from Earth, the star itself shows subtle changes in brightness in TESS observations, which can be used to measure the star’s radius, mass and age, a known method. In asteroseismology.

At the same time, the star’s magnetic field creates a slight polarization on the star’s light, allowing PEPSI on the LBT to create a magnetic map of the star’s surface as the star rotates; this is a technique known as Zeeman-Doppler imaging. Together, these measurements allowed the team to estimate the current magnetic environment around the star.

Previous observations by NASA’s Kepler space telescope had already shown that magnetic braking can weaken significantly as the Sun ages, breaking the tight link between rotation and magnetism in older stars. However, the evidence for this change was indirect and was based on measurements of the rotation rates of stars with a wide range of ages. It was clear that rotational deceleration stopped around the age of the Sun (4.5 billion years) and that weak magnetic braking in old stars could reproduce this behavior.

But only direct measurements of a star’s magnetic field can reveal underlying causes, and the targets Kepler observed were too faint for LBT observations. The TESS mission began collecting measurements in 2018 for the closest and brightest stars in the sky, including 51 Pegasus, similar to Kepler’s observations.

Over the past few years, the team began using PEPSI on the LBT to measure magnetic fields for various TESS targets, gradually developing a new understanding of how magnetism changes in stars like the Sun as they age. Observations have shown that magnetic braking changes abruptly in stars slightly younger than the Sun, at which point it weakens by a factor of more than 10, and decreases further as stars continue to age.

The team attributed these changes to an unexpected change in the strength and complexity of the magnetic field and the impact of this change on the stellar wind. Recently measured properties of 51 Pegasi indicate that, like our own Sun, it is undergoing a transition to weakened magnetic braking.

“It’s great that LBT and PEPSI can shed new light on this planetary system, which plays such an important role in exoplanet astronomy,” says Strassmeier, principal investigator of the PEPSI spectrograph. “This research is an important step forward in the search for life in our galaxy.”

The transition of life from oceans to land in our solar system occurred several hundred million years ago, coinciding with the time when the magnetic brake on the Sun began to weaken. Young stars bombard their planets with radiation and charged particles that are hostile to the development of complex life, but older stars appear to provide a more stable environment. According to Metcalfe, the team’s findings suggest that the best places to look for life outside our solar system may be around middle and old stars.