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| Artist's renditions 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. Illustrations Credit: Navid Marvi, courtesy Carnegie Science. |
How does a star affect the makeup of its planets? And what does this mean for the habitability of distant worlds? Carnegie’s Luke Bouma is exploring a new way to probe this critical question—using naturally occurring space weather stations that orbit at least 10 percent of M dwarf stars during their early lives. He is presenting his work at the American Astronomical Society meeting this week.
We know that most M dwarf stars—which are smaller, cooler, and dimmer than our own Sun—host at least one Earth-sized rocky planet. Most of them are inhospitable—too hot for liquid water or atmospheres, or hit with frequent stellar flares and intense radiation. But they could still prove to be interesting laboratories for understanding the many ways that stars shape the surroundings in which their planets exist.
“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,” Bouma explained. “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.”
But astronomers can’t set up a space weather station around a distant star.
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Artist's renditions of the space weather around M dwarf TIC 141146667 with an overlay showing magnetic field lines.
Illustration Credit: Navid Marvi, courtesy Carnegie Science.
Or can they?
Working with Moira Jardine of the University of St. Andrews, Bouma homed in on a strange type of M dwarf called a complex periodic variable. They are young, rapidly rotating stars that observations show experience recurring dips in brightness. Astronomers weren’t sure if these dips in brightness 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,” Bouma said. “But we were able to demonstrate that they can tell us something about the environment right above the star’s surface.”
Bouma and Jardine answered that question by creating “spectroscopic movies” of one of these complex periodic variable stars. They were able to demonstrate that they are large clumps of cool plasma that are trapped in the star’s magnetosphere—basically being dragged around with the star by its magnetic field—forming a kind of doughnut shape called a torus.
“Once we understood this, the blips in dimming stopped being weird little mysteries and became a space weather station,” Bouma exclaimed. “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.”
Bouma and Jardine estimate that at least 10 percent of M dwarfs could have plasma features like this early in their lives. So, these space weather stations could help astronomers learn a great deal about particles from stars contribute to planetary conditions.
Next, Bouma hopes to reveal where the material in the torus comes from—the star itself or 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 concluded. “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.”
Reference Number: spw010726_01
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