New Jersey Institute of Technology | 2018 May 08
The Sun’s corona, invisible to the human eye except when it appears briefly as a fiery halo of plasma during a solar eclipse, remains a puzzle even to scientists who study it closely. Beginning 1,300 miles from the star’s surface and extending millions more in every direction, it is more than a hundred times hotter than lower layers much closer to the fusion reactor at the Sun’s core.
A team of physicists, led by NJIT’s Gregory Fleishman, has recently discovered a phenomenon that may begin to untangle what they call “one of the greatest challenges for solar modeling” – determining the physical mechanisms that heat the upper atmosphere to 1 million degrees Fahrenheit and higher. ...
With a series of observations from NASA’s space-based Solar Dynamics Observatory (SDO), the team has revealed regions in the corona with elevated levels of heavy metal ions contained in magnetic flux tubes – concentrations of magnetic fields – which carry an electrical current. Their vivid images, captured in the extreme (short wave) ultraviolet (EUV) band, reveal disproportionally large – by a factor of five or more - concentrations of multiply charged metals compared to single-electron ions of hydrogen, than exist in the photosphere.
The iron ions reside in what the team calls “ion traps” located at the base of coronal loops, arcs of electrified plasma directed by magnetic field lines. The existence of these traps, they say, implies that there are highly energetic coronal loops, depleted of iron ions, which have thus far eluded detection in the EUV range. Only metal ions, with their fluctuating electrons, produce emissions which make them visible. ...
Ion Traps at the Sun: Implications for Elemental Fractionation - Gregory D. Fleishman et al
- Astrophysical Journal 857(2):85 (2018 Apr 20) DOI: 10.3847/1538-4357/aab54c
arXiv.org > astro-ph > arXiv:1803.02851 > 07 Mar 2018