Over the past decade, our study of the Sun has seen significant progress as multiple spacecraft have observed Earth's host star up close. And yet, there is still so much we don't know about the large star that greets our skies every day.
Chief among questions about the Sun might be what controls its violent flareups.
In order to answer this question, a team of astronomers recently took a counterintuitive approach. They took a step back, looking at the Sun as if it were a distant, unfamiliar star.
The new findings were detailed in a study published Thursday in the Astrophysical Journal, and not only gives scientists new insight about stellar activity, but helps them understand life around other stars as well.
The team of scientists behind the study looked at sunspots at low resolution as if they were located trillions of miles away.
Sunspots are dark spots that mark the Sun's surface. They are caused by the magnetic field inhibiting the transfer of energy on the surface of the Sun through the process of convection, where hot fluid rises and cooler fluid sinks.
Therefore, sunspots are an indication of solar activity.
As the solar cycle reaches its halfway point, the Sun reaches its 'solar maximum' where the most amount of sunspots can be seen across its surface. When the solar cycle reaches its end, there are fewer sunspots, a period known as solar minimum.
“We wanted to know what a sunspot region would look like if we couldn’t resolve it in an image,” Shin Toriumi, a scientist at the Institute of Space and Astronautical Science at Japan Aerospace Exploration Agency, and lead author of the new study, said in a statement. “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.”
The data created a simulated view of distant stars, looking at the effect of sunspots on the atmosphere of a star as though it was not our Sun.
“The Sun is our closest star. Using solar observing satellites, we can resolve signatures on the surface 100 miles wide,” Vladimir Airapetian, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland and co-author of the new study, said in a statement. “On other stars, you might only get one pixel showing the entire surface, so we wanted to create a template to decode activity on other stars.”
The team of scientists observed the star as though there was only one group of sunspots across the entire surface, a rare occurrence, in order to gather more details. What they found was that light curves differed when they were measured at different wavelengths.
When one sunspot appears at the center of the Sun in visible light, the Sun is dimmer. However, when the sunspot group is near the edge of the Sun, the star appeared brighter.
This could be explained due to the Sun's faculae, a bright region on the surface of the Sun that is linked to the appearance of sunspots. Near the edge of the Sun, the hot walls of the faculae's nearly vertical magnetic fields become increasingly visible.
“So far we’ve done the best-case scenarios, where there’s only one sunspot visible,” Toriumi said. “Next we are planning on doing some numerical modeling to understand what happens if we have multiple sunspots.”
Since sunspots are a good indication of solar activity, scientists are using them to help them understand and better predict space weather.
Space weather is controlled primarily by the Sun periodically ejecting boiling-hot plasma, in the form of solar flares and solar wind, across the Solar System. These ejections cause magnetic storms in the Earth's upper atmosphere, which can have major effects on the power grids on Earth, as well as orbiting spacecraft and astronauts.
Abstract: Major solar flares are prone to occur in active-region (AR) atmospheres associated with large, complex, dynamically evolving sunspots. This points to the importance of monitoring the evolution of starspots, not only in visible but also in ultraviolet (UV) and X-rays, in understanding the origin and occurrence of stellar flares. To this end, we perform spectral irradiance analysis on different types of transiting solar ARs by using a variety of full-disk synoptic observations. The target events are an isolated sunspot, spotless plage, and emerging flux in prolonged quiet-Sun conditions selected from the past decade. We find that the visible continuum and total solar irradiance become darkened when the spot is at the central meridian, whereas it is bright near the solar limb; UV bands sensitive to the chromosphere correlate well with the variation of total unsigned magnetic flux in the photosphere; amplitudes of extreme ultraviolet (EUV) and soft X-ray increase with the characteristic temperature, whose light curves are flat-topped due to their sensitivity to the optically thin corona; the transiting spotless plage does not show the darkening in the visible irradiance, while the emerging flux produces an asymmetry in all light curves about the central meridian. The multiwavelength Sun-as-a-star study described here indicates that the time lags between the coronal and photospheric light curves have the potential to probe the extent of coronal magnetic fields above the starspots. In addition, EUV wavelengths that are sensitive to temperatures just below 1 MK sometimes show antiphased variations, which may be used for diagnosing plasmas around starspots.