A team of Indian astrophysicists are finding out the reason why the sun has been weakening decade over decade. This impacts daily life on earth because it can disturb Global Positioning Signals (GPS), long-distance radio communications, and power grids.

Scientists have been tracing the intensity of solar activity during the last 100 years. Now, a team of Indian astrophysicists say that the sun has been much quieter between 2008 and 2019 than it was between 1996 and 2007. This quietness over the past 10 years is an area of interest for scientists, astrophysicists in particular.

While there is agreement that the sun is hushing up itself with its solar storms getting smaller, there is a curiosity among scientists to know why exactly this is happening.

Now, a joint team of Indian researchers is studying this phenomenon through the lens of the sun’s coronal mass ejections or CMEs. The scientists come from the Indian Institute of Astrophysics, the M P Birla Institute of Fundamental Research and the Udaipur Solar Observatory.

What are coronal mass ejections?

The sun has a magnetic field of its own. All planets and stars in our solar system have their own magnetic fields. (The magnetic fields of Venus and Mars is too small to measure though. At least one star out there has a magnetic field larger than the sun’s – the Tiny Red Dwarf Star.)

The sun is active with sunspots, solar flares and CMEs. The sun’s magnetic field causes instabilities on its surface. Coronal mass ejections, or CMEs, are giant expanding bubbles of magnetized plasma erupting from the surface of the sun out into the space from time to time due to instabilities in the its magnetic field.

CMEs can launch a billions of tons of super-heated gas into space, most of which drifts harmlessly across the solar system. Occasionally one of these is directed at the earth.

The intensity of such solar activity is known to vary in decade-plus periodic cycles. Understanding the propagation of CMEs is important since these disturb earth’s magnetosphere.

Are the CMSs getting smaller?

The answer to the question is an emphatic yes! And finding out why is the astonishing discovery of the Indian scientists.

The team has concluded that the size of CMEs between 2008 and 2019 is only two-thirds their size in the previous decade. They are startled by this decrease in the mass, size and the internal pressure of the explosive gurgling bubbles.

The scientists did not expect this decrease in the size of the CMEs. On the contrary, astrophysicists had surmised that the decrease in the pressure in the (CMEs’) outer world would increase in radial size of CMEs. As one scientist explained: “Just imagine you have a bubble of gas in a vacuum that will not stop it from growing larger. That is the type of space the effervescent CMEs live in – but they have defied this logic.”

Explaining how and why this logic has been defied, Dr. Wageesh Mishra suggests: “The reduced pressure in the interplanetary space (or the CMEs outside world) is compensated by a reduced magnetic content inside CMEs. This did not allow the CMEs to expand enough”. Mishra is from the Indian Institute of Astrophysics.

The team also established that the gas pressure in the interplanetary space in the last decade they were studying was only 40 per cent of the pressure in the previous decade. Solar activities are measured by the number of sun spots. One would expect that the ejections would also reduce. In terms of CMEs, the rate at which the Sun has been losing its mass through these episodic ejections had also reduced by 15 per cent.

Why is the study of CMEs so vital?

The sun is known to be very active with sunspots, solar flares, and CMEs. Mishra says that understanding this is important because this solar activity effects life on earth.

CMEs dictate a host of taken-for-granted modern day necessities because they disturb the near-earth space environment, in turn disturbing the orbit of satellites in low-earth orbits. This further disturbs global positioning signals (GPS), long-distance radio communications, and power grids are dependent on the CMEs, Dr Mishra says.

The intensity of such solar activity is known to vary in decade-plus periodic cycles. It had earlier been traced that the last cycle (cycle 24 between 2008 and 2019) was weaker than the previous one (cycle 23 between 1996 and 2007), and the sun was weakest in 2019 during the last 100 years.