Carnegie’s Luke Bouma shared groundbreaking research at the American Astronomical Society meeting, demonstrating that large clumps of cool plasma trapped in an M dwarf star’s magnetosphere can act as “space weather stations”, providing insight into how stellar particles influence planetary environments.
Artist's rendition of the space weather around M dwarf TIC 141146667. The torus of ionized gas is sculpted by the star's magnetic field and rotation, with two pinched, dense clumps present on opposing sides of the star. Image Credit: Illustrations by Navid Marvi, Carnegie Science
How do stars shape the composition of their planets, and what implications does this have for the habitability of distant worlds? Luke Bouma is investigating a novel approach to address this question, by studying naturally occurring space weather stations present around at least 10 % of M dwarf stars during their early evolution.
M dwarf stars are smaller, cooler, and dimmer than the Sun. Most of them are known to host at least one Earth-sized rocky planet. While many of these planets are inhospitable, being either too hot for liquid water, lacking stable atmospheres, or exposed to frequent stellar flares and intense radiation. However, they still offer valuable opportunities to study how stars influence the environments around their planets.
Stars influence their planets. That’s obvious. They do so both through light, which we’re great at observing, and through particles or space weather like solar winds and magnetic storms, which are more challenging to study at great distances. And that’s very frustrating, because we know in our own Solar System that particles can sometimes be more important for what happens to planets.
Luke Bouma, Carnegie Science
But How do you set up a space weather station around a distant star?
Collaborating with Moira Jardine from the University of St. Andrews, Bouma focused on an unusual class of M dwarfs known as complex periodic variables. These are young, rapidly rotating stars that exhibit recurring dips in brightness. Until now, astronomers were uncertain whether these dips were caused by starspots or by material orbiting the star.
For a long time, no one knew quite what to make of these oddball little blips of dimming. But we were able to demonstrate that they can tell us something about the environment right above the star’s surface.
Luke Bouma, Carnegie Science
Bouma and Jardine addressed this question by producing “spectroscopic movies” of a complex periodic variable star. Their observations revealed that the dips in brightness are caused by large clumps of cool plasma trapped within the star’s magnetosphere. These clumps are carried along by the star’s magnetic field, forming a doughnut-shaped structure known as a torus.
Once we understood this, the blips in dimming stopped being weird little mysteries and became a space weather station. The plasma torus gives us a way to know what's happening to the material near these stars, including where it’s concentrated, how it’s moving, and how strongly it is influenced by the star’s magnetic field.
Luke Bouma, Carnegie Science
Bouma and Jardine estimate that at least 10 % of M dwarfs may host plasma features like this during their early stages. These natural space weather stations could provide astronomers with valuable insights into how stellar particles influence planetary environments.
Bouma’s next goal is to determine the origin of the torus material, whether it comes from the star itself or from an external source.
“This is a great example of a serendipitous discovery, something we didn’t expect to find but that will give us a new window into understanding planet-star relationships,” Bouma concludes. “We don't know yet if any planets orbiting M dwarfs are hospitable to life, but I feel confident that space weather is going to be an important part of answering that question.”