New Study Reveals Unexpectedly Strong Magnetic Fields in Stars and Their Implications for Astrophysics and Exoplanets

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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, the surface magnetism is linked to the star’s rotation, a process similar to how the interior of a hand-held flashlight works. Strong magnetic fields arise in the cores of magnetic sunspots, and cause various space weather phenomena. Until recently, low-mass stars—celestial bodies that have a mass less than our Sun and can rotate very quickly or relatively slowly—were expected to exhibit very low levels of magnetic activity, an assumption that makes them ideal host stars for habitability. planet.

In a new study published today in the Journal of Astrophysics, Ohio State University researchers suggest that a new internal mechanism called nuclear-mantle separation — when the surface and core of a star start rotating at the same speed, then deflects — may be responsible for increasing the magnetic field. magnetism in cold stars, a process that can intensify their radiation over billions of years and affect the habitability of nearby exoplanets.

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

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

For decades, it was assumed that the physical processes of lower mass stars followed those of solar stars. Because the star gradually loses angular momentum as it rotates downward, astronomers can use the star’s spin as a tool to understand the nature of the star’s physical processes, and how they interact with their companions and their environment. However, Kao said, there are times when the rotational clock of a star appears to have stopped in place.

Use of public data from Sloan Digital Sky Survey To study a sample of 136 stars in M44Also known as the Praesepe cluster, or Honeycomb, 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 the most exciting discoveries from the Kao team was the determination that the magnetic fields of these stars may be unusual – much stronger than current models predict. .

“Seeing the relationship between magnetic enhancement and rotational anomalies is very exciting,” said Cao. “This suggests that there may be some interesting physics at play here.” The team also hypothesized that the process of synchronizing the core and stellar envelope could cause the magnetism present in these stars to have a very different origin from the kind seen in the Sun.

“We found evidence that there is a different type of dynamo mechanism driving the attraction of these stars,” said Kao. “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 increased magnetism are more likely to hit their planets with high-energy radiation,” said Cao. “This effect is thought to last for billions of years in some stars, so it’s important to understand what might happen to our ideas of habitability.”

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

“The next thing to do is to verify that the increase in attractiveness is occurring on a much larger scale,” said Cao. “If we can understand what’s going on inside these stars when they’re experimenting with shear-amplified magnetic forces, it will point science in new directions.”

further information:
Lyra Cao et al, Envelope separation driver driven by a core radial shear armature in Cool Stars, Journal of Astrophysics (2023). DOI: 10.3847/2041-8213/acd780

Journal information:
Astrophysics Journal Letter

2023-07-18 00:45:27
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