Rice University researchers have demonstrated that stars such as the sun exhibit dynamic surface behaviors that can influence their magnetic and energetic environments. The key to understanding whether or not a star can support life-sustaining planets is its stellar magnetic activity. NASA CreditRice University researchers discovered that stars scattered across the cosmos may look very different but are more alike than previously thought.Rice scientists have discovered that stars such as the sun exhibit dynamic surface behaviors that can influence their magnetic and energetic environments. This stellar magnetic activity determines whether a star is home to planets that could support human life.Rice postdoctoral researcher Alison Farrish, and astrophysicists David Alexander (and Christopher Johns-Krull) published their work in an article in The Astrophysical Journal. This research links the motion of cool stars to the surface magnetic flux that drives their coronal Xray luminosity. It could be used to predict how magnetic activity will affect any exoplanets within their systems.Farrish and Alexander led another study that found that a star's "weather" could make some planets in its "Goldilocks" zone uninhabitable.Farrish stated that all stars lose angular momentum over their lives and become less active. We believe that the sun was more active in the past, which may have had an impact on Earth's early atmospheric chemistry. Exoplanet research is a lot easier if you think about the long-term effects of higher energy emission stars on Earth.Johns-Krull stated that models originally designed for the sun are being taken and tested to adapt to starlight.Based on limited data, the researchers attempted to model far-flung star systems. It was possible to determine the spin and flux of certain stars, as well as their classificationtypes F. G. K. M, which provided information about their sizes, and temperatures.They compared the properties and characteristics of the sun, G-type star, using its Rossby number. This is a measure of stellar activitiy that includes its speed of rotation and subsurface fluid flows. It influences the distribution of magnetic flux at a star's surface. They found that the "space weather" of each star influences conditions on their planets in a similar way.Alexander stated that the study showed stars at least cool stars are not too different from one another. Alison's model is a good one to use when looking at exoplanets surrounding M, F, or K stars.It also suggests something more intriguing for established stellar Physics, that the process of creating a magnetic field may be very similar in all cool star systems. He said that it was a bit surprising. This could be stars that, like the sun, have convective down at their cores.Johns-Krull stated that all stars, including the sun, fuse hydrogen and helium within their cores. That energy is then carried first in the radiation from photons towards the surface. It hits a zone between 60% and 70% of the way, which is just too opaque for it to be convection. The energy radiates out of the hot matter, while the cooler matter is pushed down.He said that stars less than one-third of the mass of sun have no radiative zones. They are convective all over. Many theories about how stars create a magnetic field depend on the existence of a boundary between radiative and convection zones. Therefore, it is not surprising that stars with no boundary would behave differently. After accounting for their unique characteristics, this paper shows that they behave in many ways just like the sun.Farrish, who has just received her doctorate from Rice, will soon begin a postdoctoral assignment at NASA's Goddard Space Flight Center. She noted that the model only applies to unsaturated stars.Farrish stated that the most magnetically active stars were those we call "saturated". "An increase in magnetic activity does not always show an increase in high-energy X-ray emissions after a certain point. It is still unknown why more magnetic activity on the star's surface does not result in more emission.She stated, "Conversely, we see a correlation between magnet activity and energetic emission at the sun's unsaturated regime." "That occurs at a lower activity level and stars that are more stable to magnetic activity might be more attractive because they may provide more favorable environments for planets."Alexander stated that the observation, which cover four types of spectral type, including partially and fully convective, can be fairly well represented using a model created from the sun. It also supports the idea that a star 30 times more active that the sun might not be a G class star can still be captured by the analysis Alison did.He said, "We must be clear that our simulations are not attempting to simulate any particular star or system." "We are stating that statistically, the magnet behavior of an M star with a typical Rossby value behaves in a similar manner to the sun. This allows us to evaluate its potential impact on the planets.The star's activity cycles are a critical wildcard. Without years of observation, they can't be included in the models. Sunspot activity is when the sun's magnetic field lines are most distorted, indicating that it has a 11-year cycle.Johns-Krull stated that the model will continue to be useful in many different ways. He said, "One of my interests is studying very young star, many of them, like low-mass, fully convective." Many of these stars have disc material surrounding them, and are still forming new planets. We believe that the stellar magnetic field mediates their interaction."So, Alison can use her modeling work to learn about the large scale structure of very magnetically active stars. This can then be used to test ideas about how these young stars interact with their disks."Minjing Li, a visiting student from the University of Science and Technology of China is co-author of this paper. Alexander is a professor in physics and director at the Rice Space Institute. Johns-Krull teaches physics and astronomy.Continue reading Magnetic fields are implicated in the mysterious midlife crisis for starsAdditional information: Alison O. Farrish and colleagues, Modeling Stellar Activity Rotation Relations in Unsaturated cool stars, The Astrophysical Journal (2021). Information from the Astrophysical Journal Alison O. Farrish and colleagues, Modeling Stellar Activities-rotation Relationships in Unsaturated Cool Stars (2021). DOI: 10.3847/1538-4357/ac05c7
