NASA’s vast fleet of spacecraft allow scientists to study the Sun up close – one of the agency’s spacecraft is even flying through the Sun’s outer atmosphere. But sometimes taking a step back can provide new perspectives.
In a new study, scientists looked at sunspots – darkened spots on the Sun caused by its magnetic field – at low resolution as if they were trillions of miles away. This resulted in a simulated view of distant stars, which can help us understand stellar activity and living conditions on planets orbiting other stars.
“We wanted to know what a sunspot region would look like if we couldn’t resolve it into an image,” said Shin Toriumi, lead author of the new study and a scientist at JAXA’s Institute for Space and Astronautics. “So we used the solar data as if it came from a distant star to have a better connection between solar physics and stellar physics.”
Sunspots are often precursors of solar flares – intense bursts of energy from the surface of the Sun – so it’s important to monitor sunspots to understand why and how flares occur. Additionally, understanding the frequency of flares on other stars is one of the keys to understanding their chances of harboring life. Having a few rashes can help build complex molecules like RNA and DNA from simpler building blocks. But too many powerful flares can strip entire atmospheres, rendering a planet uninhabitable.
To see what a sunspot would look like and its effect on the solar atmosphere on a distant star, scientists began with high-resolution data from the Sun from NASA’s Solar Dynamics Observatory and the Hinode mission of JAXA / NASA. By summing up all the light in each image, the scientists converted the high-resolution images into single data points. By chaining the following data points together, the scientists created graphs showing how light changed as the sunspot passed through the rotating face of the Sun. These graphs, which scientists call light curves, showed what a sunspot passing over the Sun would look like if it were several light years away.
“The sun is our closest star. Using solar observation satellites, we can resolve signatures over an area 100 miles wide, ”said Vladimir Airapetian, co-author of the new study and astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. . “On other stars you might only get one pixel showing the entire surface. So we wanted to create a model to decode the activity on other stars.”
The new study, published in the Astrophysics Journal, examined simple cases where there is only one group of sunspots visible on the entire face of the Sun. Even though NASA and JAXA missions have continuously collected observations of the Sun for over a decade, these cases are quite rare. Usually there are either multiple sunspots – like during solar maximum, which we are heading towards now – or none at all. In all these years of data, scientists have only found a handful of examples of a single isolated sunspot cluster.
By studying these events, scientists found that the light curves differ when they measure different wavelengths. In visible light, when a singular sunspot appears in the center of the Sun, the Sun is weaker. However, when the sunspot cluster is near the edge of the Sun, it is actually brighter due to the faculae – bright magnetic features around the sunspots – because near the edge, the hot walls of their almost vertical magnetic fields become more and more visible.
Scientists also looked at light curves in x-rays and ultraviolet light, which show the atmosphere above the sunspots. As the atmospheres above the sunspots are magnetically heated, scientists have found brightening at certain wavelengths. However, scientists also unexpectedly discovered that heating can also cause light from the atmosphere to attenuate at low temperatures. These results may provide a tool for diagnosing the environments of spots on stars.
“So far we’ve done the best scenarios, where there’s only one visible sunspot,” Toriumi said. “Next, we plan to do some digital modeling to figure out what happens if we have multiple sunspots.”
By studying stellar activity on young stars in particular, scientists can get an idea of what our young Sun might have looked like. This will help scientists understand how the young Sun – which was darker overall but active – impacted Venus, Earth, and Mars in their early days. It could also help explain why life on Earth began four billion years ago, which some scientists say is linked to intense solar activity.
Studying young stars may also help scientists understand what triggers superflares – those that are 10 to 1,000 times more powerful than the largest views of the Sun in recent decades. Young stars are generally more active, with superfares almost every day. Whereas, on our more mature Sun, they can only occur once every thousand years or so.
Spotting the young suns suitable for supporting habitable planets helps scientists who focus on astrobiology, the study of original evolution and the distribution of life in the universe. Several next-generation telescopes in production, which will be able to observe other stars in x-ray and ultraviolet wavelengths, could use the new results to decode observations of distant stars. In turn, this will help identify those stars with appropriate levels of lifelong stellar activity – and this can then be followed by observations of other upcoming high-resolution missions, such as the James Webb Space Telescope at the NASA.