Old stars may be the best place to look for life  Urania

Scientists have long assumed that magnetic suppression of stellar rotation persists indefinitely, but new observations challenge these assumptions.

Once upon a time, scientists assumed that stars operated on a perpetual magnetic brake, causing their rotation to slow down indefinitely. Thanks to new observations and advanced methods, they were able to delve deeper into the magnetic secrets of stars and discovered that it was not what they expected. Cosmic hotspots for finding alien neighbors may be around stars that are going through a midlife crisis and beyond. The results of this pioneering research shed light on magnetic phenomena and habitable environments published Th Astrophysical Journal Letters.

In 1995, Swiss astronomers Michael Mayor and Didier Queloz announced the first discovery of a planet outside our own. Solar System. This planet revolves around a distant sun-like star known as 51 Pegasus. Since then, more than 5,500 people have been called egzoplanetWhich revolves around other stars Our galaxy. In 2019, both scientists received the Nobel Prize in Physics for their pioneering work. In the first half of January 2024, an international team of astronomers published new observations of 51 Pegasi, suggesting that the current magnetic environment around this star may be particularly favorable for the evolution of complex life.

Stars like the Sun are born by rotating rapidly, creating powerful stars Magnetic fieldWhich could explode violently and bombard their planetary systems with charged particles and harmful radiation. Over billions of years, the stars' rotation gradually slows down as the magnetic field is pulled down by winds flowing from their surfaces, a process known as magnetic braking. Slower rotation results in a weaker magnetic field, and both properties gradually decrease, as they influence each other. Until recently, astronomers assumed that magnetic braking continues indefinitely, but new observations are beginning to challenge this assumption.

We're rewriting the textbooks on how spin and magnetism change in older stars like the Sun after their half-life said team leader Travis Metcalfe, a senior research fellow at White Dwarf Research Foundation In Golden, Colorado, USA. Our results have important implications for stars with planetary systems and their prospects for the development of advanced civilizations. Klaus Strassmeier, director of the Leibniz Institute for Astrophysics in Potsdam, Germany, and co-author of the study, adds: This is because weak magnetic braking also stifles stellar winds and reduces the possibility of destructive explosions.

A team of astronomers from the United States and Europe combined observations of 51 Pegasi from the satellite he-goat With the magnetic field measurements he made Large Binocular Telescope (LBT) In Arizona using the tool Polarimetry and Spectroscopy Instrument Potsdam Eichel (Pepsi). Although the exoplanet does not pass in front of the star from our perspective, small changes in the star's brightness allow us to measure the star's radius, mass, and age (Astroseismology). The star's magnetic field allowed it to create a magnetic map of its surface as it rotated (Zeeman-Doppler imaging). These measurements allowed the team to evaluate the current magnetic environment around the star.

Already previous notes from Kepler telescope It has been suggested that magnetic damping may weaken after the age of the Sun (4.5 billion years), breaking the close relationship between spin and magnetism in older stars. However, only direct measurements of the star's magnetic field can pinpoint the cause, and the targets observed by Kepler were too faint to be observed with an LBT. The TESS mission began collecting measurements in 2018, including 51 pegasi.

In recent years, the team began using PEPSI on the LBT to measure the magnetic fields of several TESS targets, allowing them to gain new knowledge about how magnetism in stars changes as they age. Observations have shown that magnetic damping changes suddenly in stars slightly younger than the Sun, becoming more than 10 times weaker at this point, and decreasing further as the star ages. The team attributed these changes to an unexpected shift in the strength and complexity of the magnetic field and the effect of this shift on stellar winds. New measurements of the properties of 52 Pegasi show that the star has already undergone this transition to weak magnetic braking, just like our Sun.

It is extremely gratifying that LBT and PEPSI have been able to reveal new insights into this planetary system that has played a major role in exoplanetary astronomy. – says Klaus Strassmeyer, principal investigator of the Pepsi spectrometer. This research is an important step forward in the search for life in our galaxy.

In our solar system, the transition from oceans to land occurred hundreds of millions of years ago, coinciding with the weakening of the Sun's magnetic braking. Young stars bombard their planets with charged particles, which can be hostile to the development of complex life, while older stars appear to provide a more stable environment. The team's findings suggest that the best places to look for life outside our solar system may be middle-aged stars and older stars.

Agnieszka Novak

more information:

Source: AIP

Pictured: A composite image showing the 51 Pegasi system and its measured magnetic field. Source: AIP/J. Vollmeister

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