Astronomers discover startling evidence of ‘unusual’ stellar evolution

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Astronomers have found evidence that some stars boast unexpectedly strong surface magnetic fields, a finding that challenges current models of how they evolve.

In stars like our sun, surface magnetism is linked to stellar rotation, a process similar to the inner workings of a handheld flashlight. Strong magnetic fields appear in the cores of magnetic sunspot regions, and cause a variety of space weather phenomena. Until now, low-mass stars—celestial bodies with less mass than our Sun and can rotate either very quickly or relatively slowly—were thought to exhibit very low levels of magnetic activity, an assumption that made them ideal host stars for habitability. planets.

In a new study published today in Astrophysical Journal LettersResearchers from Ohio State University argue that a new internal mechanism called mantle-nuclear separation — when a star’s surface and core begin to rotate at the same rate, then veer apart — may be responsible for boosting magnetic fields on cool stars, a process that can intensify their radiation for billions of years. years and affect the habitability of nearby exoplanets.

The research is made possible by a technique developed earlier this year by Lera Kao, lead author of the study and graduate student in astronomy at Ohio State, and co-author Marc Pinsonault, professor of astronomy at Ohio State, to make and describe measurements of the stars and the magnetic field.

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Although low-mass stars are the most common stars in the Milky Way and often host exoplanets, scientists know relatively little about them, Kao said.

For decades, it was assumed that the physical processes of lower-mass stars follow those of solar stars. Because stars gradually lose angular momentum as they spin downward, astronomers can use stellar spins as a tool to understand the nature of a star’s physical processes, and how it interacts with its companions and its surroundings. However, Kao said there are times when the stellar rotation clock seems to stop in place.

Use of public data from Sloan Digital Sky Survey To study a sample of 136 stars in M44a star bed also known as the Praesepe, or Beehive cluster, the team found that the magnetic fields of low-mass stars in the region appear to be much stronger than current models can explain.

While previous research has revealed that the Beehive Cluster is home to many stars that challenge current theories of rotational evolution, one of Kao’s team’s most exciting discoveries was the determination that the magnetic fields of these stars may be unusual — much stronger than current models predict.

“Seeing a link between magnetic enhancement and rotational anomalies was incredibly exciting,” said Cao. “It suggests that there may be some interesting physics at play here.” The team also hypothesized that the process of synchronizing the star’s core and envelope might induce magnetisms present in these stars that would have a very different origin than the kind seen on the Sun.

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“We found evidence that there is a different kind of dynamo mechanism that drives the magnetism of these stars,” Kao said. “This work shows that stellar physics can have surprising implications for other fields.”

According to the study, these findings have important implications for our understanding of astrophysics, particularly in the search for life on other planets. “Stars that experience this enhanced magnetism are more likely to hit their planets with high-energy radiation,” Cao said. “This effect is expected to last for billions of years on some stars, so it is important to understand what it might do to our ideas about habitability.”

But these findings should not discourage the search for an extraterrestrial presence. With further research, the team’s discovery could help provide more information about where to look for planetary systems capable of hosting life. But here on Earth, Kao believes her team’s discoveries could lead to better simulations and theoretical models of stellar evolution.

“The next thing to do is to verify that enhanced magnetism occurs on a much larger scale,” Cao said. “If we can understand what’s going on in the interiors of these stars as they experiment with shear-enhanced magnetism, it will lead science in a new direction.”

more information:
Lyra Cao et al, Core radial shear dynamo-driven envelope separation drivers in Cool Stars, Astrophysical Journal Letters (2023). DOI: 10.3847/2041-8213/acd780

Journal information:
Astrophysical Journal Letters

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