Magnetic waves explain the mystery of the sun’s outer layer

The Sun’s extremely hot outer layer, the corona, has a very different chemical makeup than the cooler inner layers, but the reason has baffled scientists for decades.

One explanation is that in the middle layer (the chromosphere), magnetic waves exert a force that separates the plasma from the Sun into different components, so that only ionic particles are carried in the corona, while leaving neutral particles behind. (thus leading to an accumulation of elements such as iron, silicon and magnesium in the outside atmosphere).

Now, in a new study published in The astrophysical journal, the researchers combined observations from a telescope in New Mexico, United States, with satellites located near Earth to identify a link between magnetic waves in the chromosphere and areas of ionized particles abundant in the warm outdoor atmosphere.

Lead author Dr Deborah Baker (UCL Space & Climate Physics) said: “The different chemical compositions of the inner and outer layers of the Sun were first noted over 50 years ago. This discovery generated what is one of the longest open questions in astrophysics.

“The difference in composition is surprising, given that the layers are physically linked, and the material in the crown comes from the innermost layer, the photosphere.

“Now, thanks to a unique combination of terrestrial and space observations of the solar atmosphere, carried out almost simultaneously, it has been possible to definitively detect the magnetic waves in the chromosphere and relate them to an abundance of elements in the corona. which are not found in the interior regions of the Sun.

“Identifying the processes that shape the corona is crucial as we try to better understand the solar wind, a flow of charged particles flowing from the Sun outwards, which can disrupt and damage satellites and infrastructure on Earth.

“Our new findings will help us analyze the solar wind and trace it to where it originated in the Sun’s atmosphere.”

The findings build on those of a related article by several of the same authors, published last month in the Philosophical Transactions of the Royal Society, which unambiguously detected magnetic waves in the chromosphere, ruling out other factors that could have generated similar magnetic oscillations.

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

The research team behind the new paper traced the direction of the waves by modeling a range of magnetic fields and found that the waves reflecting in the chromosphere appeared to be magnetically related to areas of ionized particles abundant in the corona. .

Dr Marco Stangalini (Italian Space Agency and National Institute of Astrophysics, Rome), co-author of the two papers, said: “The difference in chemical composition between the inner layer, the photosphere and the crown is not just a characteristic of our own Sun, but stars throughout the Universe. So by observing our local laboratory, the Sun, we can improve our understanding of the Universe far beyond. “

Both papers used observations acquired by IBIS, the high-resolution spectropolarimetric imager from the Dunn Solar Telescope in New Mexico, as well as imaging from the EUV Imaging Spectrometer (EIS) at the Hinode Solar Observatory in Japan / UK / US (an instrument designed and built by a team led by UCL) and data from the NASA Solar Dynamics Observatory (SDO).

The researchers say their findings provide a basis for future research using data from the Solar Orbiter, a European Space Agency mission that acquires close-up images of the Sun. The mission, launched last February, includes instruments offered, designed and built at UCL.