Recently, an international team led by Ángela Santos, a researcher at the Spanish Institute of Astrophysics and Space Sciences, successfully measured for the first time the magnetic field of Beta Hydri—a nearby subgiant star similar to the Sun. The research results, published in the journal Astronomy & Astrophysics, reveal an unexpectedly strong magnetic braking phenomenon in this star, providing strong support for the concept of a "born-again dynamo" in subgiant stars.

Santos stated: "In recent years, we have discovered that the evolution of stellar magnetic activity is far more complex than we previously thought. Studying solar-like stars, particularly those at different evolutionary stages, is crucial for building a comprehensive picture of how stars and their systems age." Beta Hydri, one of the brightest stars visible to the naked eye in the southern sky, has long been used as a model for understanding the Sun's eventual evolution into a subgiant.

The research team used the HARPSpol instrument on the European Southern Observatory's 3.6m telescope at La Silla, Chile, to obtain high-precision spectropolarimetric data, enabling the first direct estimate of the star's surface magnetic field. By combining the magnetic field measurements with stellar parameters, the researchers calculated the current magnetic braking intensity of Beta Hydri, finding it to be several times stronger than that of the Sun.

"This clearly indicates that this star possesses a large-scale dynamo, which is surprising for a subgiant," said Santos. This discovery supports the emerging "born-again dynamo" scenario, in which subgiant stars can experience renewed magnetic activity as their outer layers expand after a typically quieter magnetic phase in midlife.

The study not only challenges traditional understanding of stellar magnetic field evolution but also positions Beta Hydri as a benchmark for testing and refining models of magnetic braking and dynamo evolution in old solar-like stars. Additionally, the research suggests that the re-ignited magnetic engine in Beta Hydri could increase space weather hazards for any nearby planets.

As the Sun's twin brother, the study of Beta Hydri provides us with a window into the future of the Sun's magnetic field, perhaps also serving as a warning bell for any planets orbiting such "retired" stars.