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Discovery of pseudo-shock waves in sun a major breakthrough

Lucknow  : The sun we look at every day in visible light has a temperature of 6000 degrees Celsius. No sunlight means no life on our planet. But its outer atmosphere (corona) produces ultraviolet (UV) and X-rays. How can this heat flow from the cold (surface of the sun) to the million-degree hot corona, and not vice versa?

The first clues to the hot corona came from the 1869 eclipse observation of the 530.3 nm green coronal line. In 1941, Nobel laureate Hannes Alfvén concluded that the sun’s corona is “heated to an extremely high temperature”.

Bengt Edlén, an eminent Swedish physicist, identified green and red emission lines observed during the solar eclipse with highly ionized iron.

After over seven decades of this Nobel-prize winning discovery, scientists are still investigating as to what extent these waves are capable of heating the solar corona to the high temperature.

The solar corona shapes the structure and dynamics of the heliosphere (a bubble-like region of space) within which all planets of our solar system reside. It constitutes an inter-planetary magnetic field and creates space weather in planetary atmospheres, including our own.

Hazardous space weather events caused by solar activity (flares, coronal mass ejections, and all sorts of eruptions) pose serious threat. This includes damaging satellite’s electronics, changing the satellite’s trajectory, increased radiation dose to astronauts in space, disrupting global positioning and navigation systems, and tripping of power grids, etc.

Various dynamical plasma processes, high-energy particles and radiation provide a platform to test theories of high-energy physics, particle physics and plasma physics, which provide significant clues to the controlled fusion, and laboratory plasma experiments to generate and control energy.

It also provides a ready reference to exploring various other astrophysical plasma sources, specifically sun-like stars and their solar systems.

Even the main science goals of the “Parker Solar Probe” mission, launched on August 12, 2018, are to trace the flow of energy and to understand the heating of the solar corona and the acceleration of the solar wind.

Various ground and space-based solar observatories have reached the sub-arcsec (one arcsec = 725 km) resolution separating the region at the sun from a few tens to a few hundred kilometres. Several existing theoretical studies of natural science have been refined and new discoveries have been made by observing and understanding the sun for decades namely, discovery of helium, Evershed flows, several forbidden line spectra, Alfvén waves, neutrino oscillations, etc.

Indian solar physics community has made outstanding contributions in developing various instruments since the establishment of Kodaikanal Observatory (formerly known as Madras Observatory) which have now been globally distributed in various research (USO/PRL, TIFR, IISc, IIA) and academic (IITs, IISERs, universities).

IIT (BHU) has a long track record of pursuing frontline research areas of solar physics starting from Skylab to Yohkoh spacecraft and later in the golden era of Solar and Heliospheric Observatory (SoHO) when several pioneering discoveries were made. Recently, IIT (BHU) has made a novel discovery under the leadership of Dr AK Srivastava and his colleagues of confined pseudo-shocks in the sun’s magnetised atmosphere. This research has been published in the leading journal “Nature Astronomy” on October 8, 2018.

Pseudo-shocks were first theorised in supersonic flows in ducts way back in 1958 which decelerate to subsonic speeds. In the sun’s atmosphere, they are not real shocks which cause only the sharp enhancement of mass density at certain localised regions. These pseudo-shocks carry enough energy and mass flux to the corona, which balance the coronal losses.

They are discovered as a new energy source in the sun’s atmosphere. The newly-discovered pseudo-shocks will play a pivotal role in the frontline area of research in solar physics and astrophysics. This discovery may well be scaled down to the controlled plasma experiments in the laboratory to provide an extensive source of “green-energy”. IIT (BHU) is at the forefront of taking this novel discovery to higher dimensions in the upcoming research.

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