Stars generate heat through thermonuclear reactions in their core and the temperature decreases towards the star’s surface. Northumbria’s Dr Richard Morto said: “The Sun is our closest star and provides a unique opportunity to study the properties of stars in detail. A number of explanations have been announced, but it wasn’t until recently that tantalizing evidence surfaced explaining this peculiar phenomenon. This is known as the sun’s coronal heating problem and has been baffling scientists ever since 1939 when the huge discrepancy was first discovered. The loops highlight the Sun’s magnetic field and are visible because they support the dense, million degree gas typical of the corona. So, what’s going on here? Energy carrying waves coming from inside the sun Magnetic loop structures in the corona of the Sun. If it weren’t enough, it’s actually about 200 times hotter than the heat source. This is one of the most intuitive laws of physics, yet as the heat travels from the sun’s surface, which registers a temperature of about 5,500 degrees Celsius, to the layer a few hundred miles away from its surface (known as the sun’s corona), it rises to a temperature of 1,000,000 degrees Celsius. This is the only instance in the known universe where the thing doing the heating is actually cooler than the thing it’s heating (along with other similar stars). In physics, the second law of thermodynamics says that heat flows naturally from an object at a higher temperature to an object at a lower temperature, and heat doesn’t flow in the opposite direction of its own accord. So, either the sun doesn’t care of the laws of physics or something more subtle is at play. At first glance, it seems that the sun’s atmosphere, called the corona, is hotter than the heat source which is preposterous given the second law of thermodynamics. One of the biggest mysteries in solar physics is how is it possible that the sun’s surface is colder than its atmosphere.

Corona of the sun