The sun is constantly changing. Material courses through not only the star itself, but throughout its expansive atmosphere. Understanding the dance of this charged gas is a key to better understand the sun.
Important questions include how the sun heats up its atmosphere, how it creates a steady flow of solar wind streaming outward in all directions, and how magnetic fields twist and turn to create regions that can explode in giant eruptions.
Now, for the first time, researchers have tracked a particular kind of solar wave as it swept upward from the sun’s surface through its atmosphere. This helps us understand how solar material travels throughout the sun.
Tracking solar waves provides a novel tool for scientists to study the atmosphere of the sun.
The imagery of the journey also confirms existing ideas, helping to nail down the existence of a mechanism that moves energy and heat into the sun’s mysteriously-hot upper atmosphere, the corona.
A study on these results is published in The Astrophysical Journal Letters. Researchers from Stanford University led the study.
They made use of data captured by NASA’s Solar Dynamics Observatory (SDO), NASA’s Interface Region Imaging Spectrograph, and the Big Bear Solar Observatory in Big Bear Lake, California.
These observatories watch the sun in 16 wavelengths of light that show the sun’s surface and lower atmosphere.
SDO takes images of the sun in many different wavelengths at a high time resolution. It can help scientists see the frequencies of these waves.
Previously, scientists have suspected that the waves they spot in the sun’s surface, called the photosphere, are linked to those seen in the lowest reaches of the sun’s atmosphere, called the chromosphere.
Now this new analysis helps scientists actually watch the waves travel up through the various layers into the sun’s atmosphere.
When material is heated to high temperatures, it releases energy in the form of light. The type, or wavelength, of that light is determined by what the material is, as well as its temperature.
That means different wavelengths from the sun can be mapped to different temperatures of solar material.
Since scientists know how the sun’s temperature changes throughout the layers of its atmosphere, they can then order these wavelengths according to their height above the surface.
The implications of this study are twofold: first, this technique for watching the waves itself gives scientists a new tool to understand the sun’s lower atmosphere.
Researchers suggest that watching the waves move upwards tells a lot about the properties of the atmosphere above sunspots – like temperature, pressure, and density. More importantly, they can figure out the magnetic field strength and direction.
The second implication of this new research is for a long-standing question in solar physics – the coronal heating problem.
The sun produces energy by fusing hydrogen at its core, so the simplest models suggest that each layer of the sun should be cooler as it moves outward.
However, the sun’s atmosphere, called the corona, is about 100 times hotter than the region below – counter to what we would expect.
No one has as-yet been able to definitively pinpoint the source of all the extra heat in the corona, but these waves may play a small role.
News source: NASA.
Figure legend: This Knowridge.com image is credited to Zhao et al/NASA/SDO/IRIS/BBSO.