Astronomers have found evidence that some stars boast unexpectedly strong surface magnetic fields, a discovery that challenges existing models of how they evolve.
In stars like our sun, surface magnetism is linked to stellar spin, a process similar to the inner workings of a hand-cranked flashlight. Strong magnetic fields are found in the hearts of magnetic sunspot regions, and cause a variety of space weather phenomena. Until now, low-mass stars—celestial bodies smaller than our sun that can rotate either very rapidly or relatively slowly—were thought to exhibit very low levels of magnetic activity, a hypothesis that first of them as ideal potentially habitable host stars. planets.
In a new study, published today in The Astrophysical Journal Lettersresearchers from The Ohio State University argue that a new internal mechanism called core-envelope decoupling—when the surface and core of a star start spinning at the same rate, then drift apart—may responsible for enhancing the magnetic field of cool stars, a process that can intensify their radiation over billions of years and affect the habitability of their nearby exoplanets.
The research was made possible thanks to a technique that Lyra Cao, lead author of the study and a graduate student in astronomy at Ohio State, and co-author Marc Pinsonneault, a professor of astronomy at Ohio State, was developed earlier this year to make and describe starpot and magnetic field measurements.
Although low-mass stars are the most common stars in the Milky Way and often host exoplanets, scientists know very little about them, Cao said.
For decades, it was believed that the physical processes of low-mass stars followed those of solar-type stars. Because stars gradually lose their angular momentum as they spin, astronomers can use stellar spin as a tool to understand the nature of the star’s physical processes, and how they interact with each other. with their partners and their environment. However, there are times when the star’s rotation clock appears to stop in place, Cao said.
Using public data from the Sloan Digital Sky Survey to study a sample of 136 stars in M44, a star crib also known as Praesepe, or the Beehive cluster, the team found that the magnetic field at low masses which stars in the region show a lot. stronger than current models can explain.
While previous research has revealed that the Beehive cluster is home to many stars that defy current theories of rotational evolution, one of the most exciting discoveries by Cao’s team is the determination that the magnetic fields of stars may be unusual — more powerful than current models predict.
“Seeing a link between magnetic enhancement and rotational anomalies is very exciting,” Cao said. “It shows that there is some interesting physics at play here.” The team also hypothesized that the process of synchronizing a star’s core and envelope could induce a magnetism found in these stars that has a different origin from the kind seen in day.
“We are looking for evidence that there is a different kind of dynamo mechanism driving the magnetism of these stars,” Cao 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, especially for the search for life on other planets. “Stars that experience this enhanced magnetism tend to bombard their planets with high-energy radiation,” Cao said. “This effect is predicted to last for billions of years in some stars, so it’s important to understand what it does to our notions of habitability.”
But these findings should not put a damper on the search for extraplanetary existence. With further research, the team’s discovery will help provide more insight into where to look for planetary systems capable of hosting life. But here on Earth, Cao believes his team’s discoveries could lead to better simulations and theoretical models of stellar evolution.
“The next thing to do is to verify that the enhanced magnetism occurs on a much larger scale,” Cao said. “If we can understand what’s happening in the interiors of these stars as they experience enhanced magnetism, it will lead science in a new direction.”
Lyra Cao et al, Core-envelope Decoupling Drives Radial Shear Dynamos in Cool Stars, The Astrophysical Journal Letters (2023). DOI: 10.3847/2041-8213/acd780
Provided by The Ohio State University
Citation: Astronomers discover unusual evidence of ‘unusual’ star evolution (2023, July 17) retrieved July 17, 2023 from https://phys.org/news/2023-07-astronomers-evidence-unusual -stellar-evolution.html
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