HAO Colloquium - The Coronal Veil

Speaker: Anny Malanushenko, HAO

Coronal loops, the enigmatic features of the solar corona, have been a subject of study for decades. It is generally agreed that they are elongated strands of emitting plasma, which are oriented along magnetic field lines. Pretty much everything else about them is subject to intense debate. A number of explanations exist for why loops do not appear to expand with height like magnetic flux tubes do, or why loops appear overdense, and a number of models have been proposed that address the size of individual strands, the plasma composition and temperature, loop heating and cooling, oscillations of associated flux tubes, etc. Many properties of coronal plasma and the coronal magnetic field can be derived from comparing the observations to theoretical models. However, most of the current models have one point in common, their concept of a loop.

It is this concept that, our study shows, might need to be reconsidered. I will present a study of a 3D MHD simulation of the solar corona generated with MURaM code (Rempel 2017). The synthetic Extreme Ultraviolet (EUV) images constructed from this simulation are remarkably realistic. The overall structure and evolution of the synthetic corona was recently shown to reproduce many important aspects of solar observations (Cheung et al, 2018). In particular, the synthetic EUV images contain bundles of realistic coronal loops. We analyze individual loops in these bundles, and attempt to identify features in the volume of the model responsible for generating these loops in the line-of-sight integrated plane-of-sky images. Based on the results of our study, in our paper submitted to ApJ we propose a new explanation for the entire phenomenon of strands seen in the EUV images of the solar corona. The explanation is strongly supported by observations of loops on the Sun, explaining some properties of loops that are challenging to address otherwise. At the same time, this explanation is not in agreement with the current interpretation of individual loops as plasma emission from individual, well-defined and spatially coherent magnetic flux tubes.

This study may lead to substantial changes in how loop observations are interpreted, challenging currently used techniques and models. How can we determine, with with solar observations, whether this is actually what is happening in the Sun? I will go over potential pitfalls for observational validation of the veil hypothesis. I will also discuss possible ways forward.

Date and time: 
Wednesday, November 17, 2021 - 2:00pm to 3:00pm