Discovery of Confined Pseudo-shocks as a New Energy Source for the Heating of Sun’s Corona

The Sun’s outer corona consists of plasma whose temperature exceeds one million degrees. This extremely hot corona is located only a few hundred kilometres above the solar surface known as the photosphere that maintains its temperature around 6000 degrees. A longstanding problem is the energy source for the corona and a mechanism that deposits this energy and heats the corona to such high temperatures. Despite numerous space and ground-based observations, and extensive theoretical efforts, the problem still remains unsolved. This is not surprising as the problem is very complex and its full solution requires a unique combination of new solar observations and novel theories dealing with the formation of the solar atmosphere and its magnetic fields. Such unique approach undertaken by a group of researches has been completed and the obtained results are briefly described in the following.

An international team including researches from nine countries, and led by Abhishek Kumar Srivastava from Department of Physics, Indian Institute of Technology (BHU), India, reports on a new discovery made by using the observations from Interface Region Imaging Spectrometer (IRIS). The observations show first ubiquitous presence of pseudo-shocks around a sunspot and the energy transfer by these pseudo-shocks into the overlying corona. The pseudo-shocks serve as substantial sources of energy and mass flux to compensate the radiative and mass losses from the solar corona located above this sunspot. The work is published recently in Nature Astronomy (Link to publication). Other team members are K. Murawski, B. Kuźma, Dariusz Wójcik from UMCS, Poland; T.V. Zaqarashvili from Space Research Institute, Graz, Austria; Marco Stangalini from INAF-OAR, Rome, Italy; Z.E. Musielak from University of Texsas, USA; J.G. Doyle from Armagh Observatory and Planaterium, N. Ireland; Pradeep Kayshap from University of South Bohemia, Czech Republic, and B.N. Dwivedi from Department of Physics, IIT (BHU).

K. Murawski, B. Kuźma and D. Wójcik from Institute of Physics, UMCS, Poland add that

This discovery provides the significant clues about new dynamical plasma processes, known as pseudo-shocks, which act as an energy source for the active solar corona to compensate its radiative losses.

This novel finding on the first observational discovery of confined pseudo-shocks will provide a new horizon to understanding the physics of the solar atmosphere and energetic processes using modern age upcoming solar telescopes from ground and space, like 2m Indian National Large Solar Telescope; DKIST, a 4m telescope in Hawaii; Parker’s Probe; Aditya-L1, etc. The work gives new insight into our understanding the energy generation, and its transport in the solar atmosphere, especially to the highly dynamic active solar corona. The consequences of this discovery are far reaching, especially for the origin of the fast streams of the solar wind and its prominent effects on heliosphere, and space-weather near our Earth and other planets in the Solar System.

Pseudo-shocks were first noticed in supersonic duct flows in 1958 by L. Crocco, which can be decelerated to subsonic velocities and were ascribed to a possible adjustment of the velocity distribution itself. Unlike shocks, pseudo-shocks exhibit discontinuities only in the mass density, and being firstly observed in Sun’s magnetized atmosphere.

Contact: K. Murawski, Department of Physics, UMCS, Lublin, Poland. Email: kmur@kft.umcs.lublin.pl

Unveiling the Origins of the Heating of the Sun’s Corona

The Sun’s outer corona exists with a temperature of a million degrees and is separated from its cool surface (the photosphere), which is 6000 degrees, by only a few hundred kilometers. A major problem in solar physics is explaining how and why the corona is so much hotter than its surface. The answer to this problem lies in the complex magnetic field which tightly woven within the atmosphere of Sun. Over the last few decades, numerous observatories in space and on the ground have provided a range of explanations for the origins of this solar coronal heating. Two competing physical mechanisms are generally accepted to explain the heating process. The first is known as magnetic reconnection, which is an explosive release of the magnetic energy, trapped in magnetic fields in the corona (otherwise known as a solar flare). The second is the energy for heating provided by oscillating magnetic fields in waves (otherwise known as Alfven waves). Detecting these magnetic field oscillations requires advanced numerical simulations combined with the highest resolution images available to solar scientists. Only now has the wave origins behind the heating of the solar corona come into full view.

An international team including researches from five countries, and lead by Professor Gerry Doyle from Armagh Observatory and Planetarium reports on a new discovery made using the Swedish Solar Telescope at La Palma, showing first ubiquitous presence of high frequency (~ 47-84 sec) waves at numerous thin magnetic flux tubes in the quiet-Sun magnetic network transferring energy into the overlying corona. They serve as substantial sources of energy flux not only to heat the solar corona but also to originate the supersonic solar wind. The work is published recently in Nature Scientific Reports (Link to artilce) lead by Dr. A.K. Srivastava from Department of Physics, Indian Institute of Technology (BHU), India. Other team members and co-workers are Juie Shetye, a PhD student at Armagh, Dr. Eamon Scullion from Northumbria University, Prof. B.N. Dwivedi from Department of Physics, Indian Institute of Technology, Varanasi, India, Prof. K. Murawski and Dariusz Wojcik from UMCS, Lublin, Poland, Dr Marco Stangalini from INAF, Rome and Professor Tom Ray from the Dublin Institute for Advanced Studies, Ireland.

Gerry Doyle and his PhD student Juie Shetye adds that “This new discovery provides a novel solution to a long-standing puzzle of the Sun’s coronal heating. This new and novel finding on what heats the corona will provide a new horizon to understanding the physics of the solar atmosphere and energetic processes using modern age upcoming solar telescopes from ground and space, like DKIST, a 4m telescope in Hawaii where Armagh Observatory are partners. This work is a new break thought on understanding the energy generation, and its transport in the localized solar atmosphere further suggests the requirement of high-resolution and sub-second observations to reveal the dynamical plasma processes at very small-scale. In addition, it is worth mentioning that Alfvén waves have been recognized to have a potential impact on a number of fields, as for example the nuclear fusion research, or black hole jets.”

Armagh Observatory and Planetarium is funded by the N. Ireland Department for Communities, while additional funding for this project came from the Leverhulme Trust and the European SolarNet programme.