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New Research Highlights Role of Magnetic Flux in Radiation Emission Signatures of Ultra-Hot Gas in Sun-like Stars

Physics Professor and NASA Scientist Vladimir Airapetian contributed to findings

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X-ray solar image of the Sun, taken by the Hinode satellite. The halo is the super-hot solar corona and the white patches on the disk are active regions, the regions of concentrated magnetic field that produce solar flares.

A new paper published in The Astrophysical Journal by Dr. Toriumi Shin from the Institute of Astronautical Science at Japanese Aerospace Exploration Agency in Tokyo, Japan, and College of Arts and Sciences Prof. Vladimir Airapetian, also a senior scientist from NASA Goddard Space Flight Center, reveals insights into the role of magnetic flux in the be observed signatures of ultra-hot gas in Sun-like stars.

“Our own Sun and stars like our Sun are magnetic stars,” Airapetian said. “Younger rapidly rotating stars produce stronger magnetic fields with its energy converted into the heat forming various layers including chromospheres, transition regions and super-hot (multi-million temperature) coronae. From time to time, this energy is being released in the form of giant explosions referred to as flares and coronal mass ejections. Because most of such stars host exoplanets, such explosions create huge amounts of X-rays and extreme UV radiation that can create detrimental conditions for habitability.”

The researchers analyzed comprehensive 10-year data from various instruments aboard Solar Dynamics Observatory (SDO) and other satellites to study how radiation that reveals the heating rates at different parts of the solar atmosphere depends on the underlying magnetic flux. Specifically, they have found a strong correlation between the energy emitted by emission lines at different wavelengths (X-ray, ultraviolet, visible light and radio waves) and the solar magnetic field. They also found that this correlation can also be applied for other solar-like stars including young suns.

The solar magnetic field plays a key role in the atmospheric heating mechanisms of the Sun. If the relationship between the magnetic field and ultra-high temperature gas in other solar-type stars can be established to be consistent with that found for the Sun, then the same mechanism should be responsible for heating the ultra-high temperature gas as in the Sun.

Toriumi and Airapetian investigated the correlation between emission lines at different wavelengths (X-rays, ultraviolet rays, visible light, and radio waves) and the surface magnetic field of the star over the wide temperature range found in the corona and chromosphere. The different wavelengths of the solar and stellar emission lines are produced at different temperatures within the star (for example, X-rays and shorter-wavelength ultraviolet rays are mainly emitted from the corona, whereas longer-wavelength ultraviolet rays and visible light emission is mainly from the chromosphere). This makes it possible to understand the gas at a variety of different temperatures by analyzing the corresponding emission lines at different wavelengths.

"It has been previously theorized that the Sun's surface magnetic field is a driver for the high temperatures in the corona and chromosphere," remarked Toriumi, lead author of the paper. "However, it was not until we saw that the correlations between the hot gas emissions at multiple wavelengths and temperatures did we realize this might be a way of predicting the production of the most energetic radiation from a star which impacts the evolution of any hosted planetary system."

This study revealed for the first time that the mechanism by which ultra-high temperature gas is heated is closely related to the magnetic field, and is universal for the Sun and other stars. Since these ultra-high temperature gases emit X-ray and ultraviolet radiation that can have a strong effect on the surrounding planets, the clarification of part of the heating mechanism from this work is a key achievement to understanding planets and exoplanets.

"This study suggests that the mechanisms of atmospheric heating in the Sun and stars have common nature. It opens a new and exciting opportunity to characterize the fluxes of ionizing radiation in the form of X-ray and extreme UV bands at the time when life started on Earth and other exoplanets to understand their impact on habitable worlds,” said Airapetian. “Our results will also help to develop observational strategies to search for signatures of life or biosignatures with the James Webb Space Telescope and other missions."

Airapetian's contributions to the study were funded by grants from Hubble Space Telescope, European Space Agency's XMM-Newton mission and NASA Planetary Science Division’s Internal Scientist Funding Model, SEEC, that aim to understand the lives of young suns.