Cold plasma torus around young red dwarfs causes periodic dimming – providing a “space weather station” to measure particles and magnetic fields from afar
Scientists have identified a surprising way to study the hidden space weather of distant stars by observing strange, recurring patterns of light dimming in Nancy. M young.
To what extent can a star shape the planets that form around it, and what does this mean for the possibility that distant worlds will ever be habitable? Luc Bouma of the Carnegie Institution is tackling this question with an unconventional approach: He is studying natural space weather stations, which are found around at least 10 percent of M-type stars in the early stages of their lives.
Astronomers already know that most M-dwarfs (which are smaller, cooler, and dimmer than our sun) host at least one rocky planet about the size of Earth. Many of these planets are likely hostile to life—too hot to support liquid water or stable atmospheres, or subject to repeated violent outbursts and high levels of radiation. Nevertheless, these systems could serve as important testbeds for understanding how stars reshape the environments their planets must contend with.
The difficulty of studying stellar weather
"Stars affect their planets. That's clear. They do it through light, which is easy to observe, and through particles—or space weather—like solar winds and magnetic storms, which are harder to study from a great distance," Bouma explained. "And that's very frustrating, because we know from our own solar system that particles can sometimes be more important to what happens to planets."
But astronomers can't set up a space weather station around a distant star.
Or is it?
Together with Moira Jardine, Bouma focused on a strange type of M dwarf called a complex periodic variable. These are young stars that rotate rapidly and exhibit repeated dips in their brightness. Until recently, researchers could not determine whether the dimming was caused by starspots on the surface, or by material surrounding the star.
"For a long time, no one knew how to interpret these strange little dimming flashes," said Bouma. "But we were able to show that we could learn something from them about the environment just above the surface of the planet."
Discovery of plasma toruses around young stars
To identify the cause, Bouma and Jardine created what they call “spectroscopic movies” of a particular complex cyclical variable star. Their results show that the dimming is related to large concentrations of cold plasma trapped in the star’s magnetosphere. The star’s magnetic field grabs this material, carrying it as the star rotates and collecting it into a doughnut-shaped body called a torus.
"Once we figured that out, the dimming flashes stopped being weird little mysteries and became a space weather station," Boma 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 strong the star's magnetic field is influencing it."
More of the topic in Hayadan:
