Research at the Carnegie Institute for Science is exploring the use of naturally occurring space weather stations that orbit at least 10% of M dwarf stars during their early lives.
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.
However, they could still prove to be interesting laboratories for understanding the many ways in which stars shape the environments in which their planets exist.
Luke Bouma, who led the research, explained: “Stars influence their planets both through light, which we’re great at observing, and through space weather like solar winds and magnetic storms, which are more challenging to study at great distances.”
Tracking complex moves on M dwarf stars
Working with Moira Jardine of the University of St Andrews, Bouma homed in on a strange type of M dwarf star 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 demonstrated that they are large clumps of cool plasma trapped in the star’s magnetosphere, forming a doughnut-shaped torus.
How dips become space weather stations
Bouma explained: “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 M dwarf 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% of M dwarfs could have plasma features like this early in their lives. Therefore, these space weather stations could help astronomers learn a great deal about how particles from stars contribute to planetary conditions.
Next steps in torus research
Next, Bouma hopes to reveal where the material in the torus comes from—the star itself or an external source.
Bouma concluded: “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.
“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.”
