Magnetic waves reveal the secret of the outer layer of Sun

The Sun’s extremely hot outer layer, the corona, has a very different chemical composition than the cooler inner layer, but the reason for this has been surprising to scientists for decades.

One explanation is that magnetic waves in the middle layer (the chromosphere) exert a force that separates the sun’s plasma into different components, so that only the ion particles are transported in the corona, while neutral particles remain (which leads to a build-up of elements such as iron, silicon and magnesium in the outer atmosphere).

Now, in a new study published in The Astrophysical Journal, researchers combined observations from a telescope in New Mexico, United States, with satellites near Earth to identify a connection between magnetic waves in the chromosphere and areas with abundant ionized particles in the warm outer atmosphere.

Chief author, dr. Deborah Baker (UCL Space & Climate Physics), said: “The different chemical compositions of the inner and outer layers of the Sun were first observed more than 50 years ago. This discovery led to one of the long-standing open questions. in astrophysics.

‘The difference in composition is astonishing, since the layers are physically linked, and that the matter in the corona arises in the inner layer, the photosphere.

‘Thanks to a unique combination of ground- and space-based observations of the sonar atmosphere, which were carried out almost simultaneously, it was possible to definitively detect magnetic waves in the chromosphere and connect them to an abundance of elements in the corona. which does not occur in the inner regions of the sun.

“Identifying the processes that make up the corona is crucial as we try to better understand the solar wind, a stream of charged particles that flow out of the sun, which can disrupt and damage satellites and infrastructure on Earth. .

“Our new findings will help us analyze the solar wind and trace it back to where it came from in the sun’s atmosphere.”

The findings build on those of a related paper by many of the same authors, which were published last month in the Philosophical Transactions of the Royal Society, which unambiguously detected magnetic waves in the chromosphere, excluding other factors that could cause similar magnetic oscillations.

The existence of magnetic waves – vibrations of ions moving in a certain direction – was first theorized in 1942 and is thought to be generated by the millions of nanoplies, or mini-explosions, that occur every second in the corona.

The research team behind the new paper tracked the direction of the waves by modeling a series of magnetic fields and found that waves reflected in the chromosphere were magnetically coupled to regions with abundant ionized particles in the corona.

Dr Marco Stangalini (Italian Space Agency and the National Institute of Astrophysics, Rome), a co-author of both articles, said: ‘The difference in chemical composition between the inner layer, the photosphere and the corona is not just a feature. of our own sun, but of stars throughout the universe. By viewing our local laboratory, the sun, we can improve our understanding of the universe far beyond. “

The two articles use observations obtained by IBIS, the high-resolution spectropolarimetric imager at the Dunn Solar Telescope in New Mexico, together with imaging of the EUV image spectrometer (EIS) on the Japan / UK / US Hinode solar observatory (an instrument designed and built by a UCL-led team) and data from the NASA Solar Dynamics Observatory (SDO).

According to the researchers, their findings are the basis for future research using data from the Solar Orbiter, a mission of the European Space Agency that obtains close-up images of the sun. The mission, launched last February, includes tools proposed, designed and built at UCL.