A new study, supported by FAPESP, demonstrates that the temperature of a plasma in the region of a solar flare is related to the “color temperature” of something known as the Lyman Spectrum (LyC), an emission of radiation in the ultraviolet range from the Sun . The research had the participation of the Brazilian Paulo José de Aguiar Simões, researcher at the Center for Radio Astronomy and Astrophysics Mackenzie.
Solar activity, which waxes and wanes in 11-year cycles, causes spots on our star’s surface due to the magnetic fields formed by rotation. The filaments of magnetic fields “trap” a part of the plasma, preventing convection (movement that makes the hot material rise and the cold fall).
With the interruption of convection, the cold plasma remains on the surface – hence the darker coloration we call a sunspot. This process is possible because the plasma, which makes up the solar surface and atmosphere, contains charged particles susceptible to magnetic fields.
Eventually, the field that formed the sunspot breaks down, releasing the plasma particles in an explosion known as a solar flare and causing solar storms and coronal mass ejections. During eruptions, the chromosphere heats up and the atomic hydrogen in the region is almost completely ionized. On the other hand, the density of the plasma causes a recombination of hydrogen.
When an electron and a proton — separated due to hydrogen ionization — collide for recombination, both particles can travel fast or slow. In the second case, the photon that the atom emits in its creation will theoretically be 13.6 eV, but in case of faster speeds, the excess energy is radiated as photons of shorter wavelength.
The ionization and recombination of hydrogen produces an emission of ultraviolet radiation with very specific properties, known as the “Lyman Continuum” (LyC). Although X-rays and gamma rays also ionize a hydrogen atom, there are far fewer of them emitted by the star’s photosphere.
The new study simulated emissions from dozens of different flares and demonstrated that the LyC color temperature is associated with the plasma temperature of the region where the emission originates. Furthermore, the research confirmed that the region reaches a local thermodynamic equilibrium between the plasma and the photons that make up the LyC.
This means that “the Lyman continuum is greatly intensified during solar flares and that analysis of the LyC spectrum can really be used for plasma diagnosis,” said Simões, a professor at the School of Engineering at Universidade Presbiteriana Mackenzie and a researcher at the Centro of Radio Astronomy and Astrophysics Mackenzie.
Article was published in The Astrophysical Journal.
Source: The Astrophisical Journal; FAPESP Agency
