Surprising Discovery: Stars Found to Possess Remarkably Strong Surface Magnetic Fields

In a groundbreaking study, astronomers have stumbled upon extraordinary evidence of “unusual” stellar evolution that challenges current models. This remarkable finding has the potential to reshape astronomers’ understanding of how stars evolve and has significant implications for the habitability of exoplanets in their vicinity, shedding light on the search for extraterrestrial life.

Surprising Magnetic Fields Observed in Stars

Astronomers have made a stunning revelation regarding certain stars—they possess unexpectedly powerful surface magnetic fields. This revelation defies the prevailing models of star evolution that have been widely accepted until now.

In stars resembling our own sun, surface magnetism is closely related to stellar spin, akin to the mechanics of a hand-cranked flashlight. Strong magnetic fields emerge in regions called magnetic sunspots, triggering various space weather phenomena. It was previously believed that low-mass stars, which are celestial bodies with less mass than the sun and can rotate either very rapidly or relatively slowly, demonstrated minimal magnetic activity. These stars were considered ideal hosts for potentially habitable planets.

Unraveling the Mystery of Magnetic Fields in Low-Mass Stars

A recent study, published in The Astrophysical Journal Letters on July 17, presents a fresh perspective on this matter. Researchers from The Ohio State University propose the existence of a novel internal mechanism called “core-envelope decoupling” that could amplify magnetic fields in cool stars. When a star’s surface and core initially rotate at the same rate and later drift apart, this mechanism could potentially intensify their radiation for billions of years. Such a phenomenon may have a profound impact on the habitability of nearby exoplanets.

The study became possible due to a technique developed earlier this year by Lyra Cao, the lead author and a graduate student in astronomy at Ohio State, along with co-author Marc Pinsonneault, a professor of astronomy at the same institution. This technique enables the creation and characterization of starspot and magnetic field measurements.

Challenging Previous Understandings of Stellar Physics

According to Cao, scientists have limited knowledge about low-mass stars, even though they are the most common stars in the Milky Way and often host exoplanets.

For decades, it was assumed that the physical processes in lower-mass stars were similar to those in solar-type stars. Astronomers use stellar spins as a tool to understand the nature of a star’s physical processes, its interactions with companions and the surrounding environment because stars gradually lose their angular momentum as they slow down their rotation. However, there are instances when the stellar rotation appears to halt, which adds complexity to the understanding of these stars, as mentioned by Cao.

Investigating the Beehive Cluster

To investigate this phenomenon further, the research team analyzed public data from the Sloan Digital Sky Survey, focusing on a sample of 136 stars in M44, also known as Praesepe or the Beehive cluster. They discovered that the magnetic fields of low-mass stars in this region appeared significantly stronger than current models could account for.

Although previous research had already indicated that the Beehive cluster is home to many stars that defy current theories of rotational evolution, one of the most intriguing findings by Cao’s team was the discovery that these stars also exhibited highly unusual magnetic fields—much stronger than predicted by existing models.

Implications for Stellar Physics and Exoplanet Habitability

Cao remarked, “To see a link between the magnetic enhancement and rotational anomalies was incredibly exciting. It indicates that there might be some interesting physics at play here.” The team also hypothesized that the synchronization of a star’s core and envelope could induce magnetism in these stars, which would have a fundamentally different origin from the magnetism observed on the sun.

Cao added, “We’re finding evidence that there’s a different kind of dynamo mechanism driving the magnetism of these stars. This work shows that stellar physics can have surprising implications for other fields.”

According to the study, these findings have significant implications for astrophysics, particularly in the search for extraterrestrial life. Cao stated, “Stars experiencing this enhanced magnetism are likely going to be battering their planets with high-energy radiation. This effect is predicted to last for billions of years on some stars, so it’s important to understand what it might do to our ideas of habitability.”

However, these findings should not discourage the pursuit of extraterrestrial existence. Further investigation could provide deeper insights into the locations of planetary systems capable of supporting life. Cao believes that on Earth, these discoveries may lead to improved simulations and theoretical models of stellar evolution.

Cao concluded, “The next step is to verify that enhanced magnetism occurs on a larger scale. If we can comprehend what happens in the interiors of these stars as they experience shear-enhanced magnetism, it will push science in a new direction.”

Reference: “Core-envelope Decoupling Drives Radial Shear Dynamos in Cool Stars” by Lyra Cao, Marc H. Pinsonneault, and Jennifer L. van Saders, 17 July 2023, The Astrophysical Journal Letters.
DOI: 10.3847/2041-8213/acd780

The study received support from The Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the National Science Foundation. Jennifer van Saders from the University of Hawaii also contributed as a co-author.

Frequently Asked Questions (FAQs) about stellar evolution

More about stellar evolution

• The Astrophysical Journal Letters: Link
• The Ohio State University: Link
• Sloan Digital Sky Survey: Link
• The Alfred P. Sloan Foundation: Link
• U.S. Department of Energy Office of Science: Link
• National Science Foundation: Link
• University of Hawaii: Link