Frequently Occurring Reconnection Jets from Sunspot Light Bridges

TL;DR

This study provides direct observational evidence of magnetic reconnection within sunspots, revealing frequent, dynamic jets and significant plasma heating at light bridges, which are crucial for understanding sunspot magnetic activity.

Contribution

First direct detection of recurrent reconnection jets in sunspots using high-resolution solar observations, highlighting their role in plasma heating and dynamic activity.

Findings

Reconnection jets frequently occur at sunspot light bridges.

Jets exhibit inverted Y-shape typical of magnetic reconnection.

Reconnection drives bidirectional flows up to 200 km/s and heats plasma to ~80,000 K.

Abstract

Solid evidence of magnetic reconnection is rarely reported within sunspots, the darkest regions with the strongest magnetic fields and lowest temperatures in the solar atmosphere. Using the world's largest solar telescope, the 1.6-meter Goode Solar Telescope, we detect prevalent reconnection through frequently occurring fine-scale jets in the H${\alpha}$ line wings at light bridges, the bright lanes that may divide the dark sunspot core into multiple parts. Many jets have an inverted Y-shape, shown by models to be typical of reconnection in a unipolar field environment. Simultaneous spectral imaging data from the Interface Region Imaging Spectrograph show that the reconnection drives bidirectional flows up to 200~km~s$^{-1}$, and that the weakly ionized plasma is heated by at least an order of magnitude up to $\sim$80,000 K. Such highly dynamic reconnection jets and efficient heating should be properly accounted for in future modeling efforts of sunspots. Our observations also reveal that the surge-like activity previously reported above light bridges in some chromospheric passbands such as the H${\alpha}$ core has two components: the ever-present short surges likely to be related to the upward leakage of magnetoacoustic waves from the photosphere, and the occasionally occurring long and fast surges that are obviously caused by the intermittent reconnection jets.