Energy release in the solar corona from spatially resolved magnetic braids

Solar observations at a resolution of 0.2 arc seconds show the reconnection and relaxation of magnetic braids in a coronal active region, leading to the dissipation of sufficient energy to heat the structures to about 4,000,000 K. A glimpse of solar corona heating The Sun's outer atmosphere, or corona, is millions of degrees hotter than its surface. The search for mechanisms capable of transferring energy from the Sun's interior to the periphery on such a scale has identified two strong candidates: wave heating is thought to heat the corona to 1.5 million K, and the reconnection and unravelling of magnetic braids has been proposed as the means of boosting the temperature towards 4 million K. New evidence to support that latter mechanism is provided by a five-minute series of images obtained by a high-resolution camera on-board a sounding rocket. The images reveal fine-scale braiding to a resolution of about 150 km in a coronal active region, and the images are consistent with energy production sufficient for the observed heating. It is now apparent that there are at least two heating mechanisms in the Sun’s outer atmosphere, or corona 1 , 2 , 3 , 4 , 5 . Wave heating may be the prevalent mechanism in quiet solar periods and may contribute to heating the corona to 1,500,000 K (refs 1 , 2 , 3 ). The active corona needs additional heating to reach 2,000,000–4,000,000 K; this heat has been theoretically proposed 6 , 7 , 8 , 9 , 10 , 11 , 12 to come from the reconnection and unravelling of magnetic ‘braids’. Evidence favouring that process has been inferred 13 , 14 , but has not been generally accepted because observations are sparse and, in general, the braided magnetic strands that are thought 1 , 2 , 3 , 15 , 16 , 17 to have an angular width of about 0.2 arc seconds have not been resolved 10 , 18 , 19 , 20 . Fine-scale braiding has been seen 21 , 22 in the chromosphere but not, until now, in the corona. Here we report observations, at a resolution of 0.2 arc seconds, of magnetic braids in a coronal active region that are reconnecting, relaxing and dissipating sufficient energy to heat the structures to about 4,000,000 K. Although our 5-minute observations cannot unambiguously identify the field reconnection and subsequent relaxation as the dominant heating mechanism throughout active regions, the energy available from the observed field relaxation in our example is ample for the observed heating.