The Solar System “breathes”, the origin of the glow that envelops the Earth has been discovered

The technological breakthrough: seeing the invisible from the L2 point

The identification of this radiation was only possible thanks to the strategic position of the eROSITA telescope, located 1.5 million kilometers from Earth. Operating from the Lagrangian point L2the instrument scanned the sky four times between 2019 and 2021, producing a clear mapping that allowed the separation of local emissions from extragalactic ones. What was once considered an insurmountable obstacle for cosmology has suddenly become a powerful diagnostic tool for heliophysics. “We were interested in studying the X-ray emission of the Milky Way, in particular the circumgalactic medium which should extend into a large sphere of plasma around our Galaxy“, explains Gabriele Ponti, one of the first authors of the work. “Analyzing the eROSITA data, we noticed significant and unexpected variations in this diffuse radiation. We understood that they could not come from distant galactic structures, which are constant, but had to be linked to a phenomenon much closer to us: the charge exchange of the solar wind“. This local component of radiation is not constant: in fact it follows the cycle of activity of the Sun, intensifying or weakening just like a cyclical breathing that modifies the appearance of the sky in the X band.

From disturbance to resource: the new frontier of heliophysics

The isolation of this signal now allows us to study the solar wind in all directions and its interaction with the interstellar medium with a precision never achieved before. “We then managed to isolate this local radiation component“, comments Konrad Dennerl, Max Planck researcher and first author of the work. “In this way, we not only reconstructed an unaltered image of the emissions coming from deep space, but also obtained valuable information on the solar wind emitted in all directions, as well as its variations over two years“.

“With this work, what was once an obstacle becomes a powerful diagnostic tool for heliophysics, allowing to study the components of the solar wind and its interaction with the interstellar medium“, concludes Ponti. “Understanding how the dynamics of the heliosphere modify the appearance of the sky in the X-ray band is fundamental to correctly interpret the warm phase of the Milky Way”.