Astronomers from The Ohio State University have found new stellar magnetic field evidence that challenges current models of how they evolve.
The new stellar magnetic field evidence suggests that some stars boast unexpectedly strong surface magnetic fields.
In stars like our Sun, surface magnetism is linked to stellar spin. This process is alike to the inner workings of a hand-cranked torch.
Strong magnetic fields are seen at the centre of magnetic sunspot regions, and cause a diverse array of space weather phenomena.
Until now, low-mass stars were thought to exhibit low levels of magnetic activity. This assumption has led to the idea that they are perfect host stars for potentially habitable planets.
However, in a new study, ‘Core-envelope Decoupling Drives Radial Shear Dynamos in Cool Stars,’ researchers have argued that the stellar magnetic field in low-mass stars is not as previously thought.
New evidence suggests that a new internal mechanism called core-envelope decouple might be responsible for enhancing magnetic fields on cool stars. This process could intensify their radiation for billions of years, subsequently impacting the habitability of nearby exoplanets.
The research, published in The Astrophysical Journal Letters, was made possible due 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, developed earlier this year to make and characterise starspot and magnetic field measurements.
Astronomers know comparatively little about low-mass stars
Low-mass stars are celestial bodies of lower mass than our Sun that can rotate either very rapidly or relatively slowly.
Although these stars are the most common in the Milky Way and often host exoplanets, scientists know comparatively little about them.
It was assumed for decades that the physical processes of lower-mass stars followed those of solar-type stars.
As stars gradually lose their angular momentum as they spin down, astronomers can use stellar spins to pinpoint the nature of a star’s physical processes. They can also be used to discover how they interact with their companions and surroundings.
However, according to the team, there are times where the stellar rotation clock appears to stop in place.
Low-mass stellar magnetic fields are much stronger than previously thought
The team used 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.
Although previous research revealed that the Beehive cluster is home to many stars that defy current theories of rotational evolution, the team discovered that the stellar magnetic field may be just as unusual.
They found that low-mass stellar magnetic fields in this region appeared to be much stronger than what current models could explain.
“To see a link between the magnetic enhancement and rotational anomalies was incredibly exciting,” said Cao. “It indicates that there might be some interesting physics at play here.”
The team also hypothesised that the process of synching up a star’s core and the envelope might induce a magnetism found in these stars that would have a different origin from those seen on the Sun.
“We’re finding evidence that there’s a different kind of dynamo mechanism driving the magnetism of these stars,” said Cao. “This work shows that stellar physics can have surprising implications for other fields.”
The work has important implications regarding stellar evolution
The new stellar magnetic field evidence has important implications for our understanding of astrophysics, particularly regarding the hunt for life on other planets.
“Stars experiencing this enhanced magnetism are likely going to be battering their planets with high-energy radiation,“ Cao said.
“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.”
These findings should not slow down the search for extraplanetary existence, however.
With further research, the stellar magnetic field discovery could provide more insight into where to look for planetary systems capable of hosting life.
Here on Earth, however, the team’s findings might lead to better simulations and theoretical models of stellar evolution.
“The next thing to do is verify that enhanced magnetism happens on a much larger scale,” said Cao.
“If we can understand what’s going on in the interiors of these stars as they experience shear-enhanced magnetism, it’s going to lead the science in a new direction.”
