With a temperature of 5,500°C, there is no denying that the surface of the Sun is hot. Yet sitting high above the star’s surface, in its upper atmosphere, a layer of gas called the corona obliterates this figure. At almost 2 million °C, it is around 300 times hotter than the Sun’s surface.
How the Sun’s corona is heated to such a temperature has remained unsatisfactorily solved, and this puzzle has become known as the coronal heating problem. In search of an answer, researchers from the National Centre for Radio Astrophysics (NCRA), India, have used a highly sensitive instrument to detect tiny flashes of radio light from all over the Sun. They believe these sparks provide the first-ever signal for numerous small magnetic explosions that collectively have sufficient energy to heat the Sun’s corona.
“Our preliminary estimates suggest that these tiny magnetic explosions should collectively have enough energy to heat the corona, which is exactly what is needed for solving the coronal heating problem,” Dr Atul Mohan, study co-author formerly of the NCRA, and now at the Rosseland Centre for Solar Physics, Norway, said in a statement.
The team’s research, published in The Astrophysical Journal Letters, relied on a telescope that went where no telescope had gone before. Whilst previous attempts had also searched for flashes of radiation as evidence for magnetic explosions, no telescope had been sensitive enough to detect the decidedly weak bursts. That is where the Murchison Widefield Array (MWA), Australia, came in.
“What made this breakthrough possible is the availability of data from a new technology instrument, the Murchison Widefield Array (MWA), and the work which we have been doing for the past few years at NCRA-TIFR to build the techniques and tools to make the most sensitive solar radio images from this data,” fellow co-author Prof. Divya Oberoi of the NCRA explained in a statement. “The very weak radio flashes we have discovered are about 100 times weaker than the weakest bursts reported till now.”
Although on their own these explosions are weak, the sheer number and presence of them all around the Sun, suggests to the researchers that together they are powerful enough to explain the origin of the corona’s extra heating system.
“What makes this really exciting is that these flashes are present everywhere on the Sun and at all times, including in the regions of weak magnetic fields, the so-called 'quiet Sun' regions,” Surajit Mondal, the lead author of this work said.