Detection of Small-Scale Granular Structures in the Quiet Sun with the New Solar Telescope

TL;DR

This study uses high-resolution solar images to identify a new population of mini-granular structures below 600 km, revealing their size distribution, spatial patterns, and fractal properties, advancing understanding of solar granulation.

Contribution

First detection and analysis of mini-granular structures in the quiet Sun, showing their size distribution, spatial confinement, and fractal nature using the New Solar Telescope.

Findings

Mini-granular structures are dominant below 600 km.

Their size distribution follows a power law with index -1.8.

Structures smaller than 600 km are multi-fractal.

Abstract

Results of a statistical analysis of solar granulation are presented. A data set of 36 images of a quiet Sun area on the solar disk center was used. The data were obtained with the 1.6 m clear aperture New Solar Telescope (NST) at Big Bear Solar Observatory (BBSO) and with a broad-band filter centered at the TiO (705.7 nm) spectral line. The very high spatial resolution of the data (diffraction limit of 77 km and pixel scale of 0.$"$0375) augmented by the very high image contrast (15.5$\pm$0.6%) allowed us to detect for the first time a distinct subpopulation of mini-granular structures. These structures are dominant on spatial scales below 600 km. Their size is distributed as a power law with an index of -1.8 (which is close to the Kolmogorov's -5/3 law) and no predominant scale. The regular granules display a Gaussian (normal) size distribution with a mean diameter of 1050 km. Mini-granular structures contribute significantly to the total granular area. They are predominantly confined to the wide dark lanes between regular granules and often form chains and clusters, but different from magnetic bright points. A multi-fractality test reveals that the structures smaller than 600 km represent a multi-fractal, whereas on larger scales the granulation pattern shows no multi-fractality and can be considered as a Gaussian random field. The origin, properties and role of the newly discovered population of mini-granular structures in the solar magneto-convection are yet to be explored.