The Dark Sun

Several hours ago, a total eclipse of the Sun occured over the southern Pacific, crossing a few isolated areas of land. Images from the eclipse have been doing the rounds via twitter, including this one (still from a live TV feed), this one, this one, this one, this one and this one. Some of them may be used to compare the appearance of the corona during the eclipse with a prediction of that appearance by magnetohydrodynamical models of the solar corona. Big word, just means modelling plasma as a hydrodynamical gas (normal stuff) influenced by magnetic fields.

But that wasn’t the only modelling of a dark sun that’s been going on. Dark matter is the stuff used to describe why the angular rotation of the middle of galactic discs is so constant when the outer stuff should be taking longer to spin round the nucleus than the inner stuff, which has a shorter distance to travel. The present model of what Dark matter is involves Weakly Interacting Massive Particles that interact with ordinary stuff and each other almost entirely through gravitational attraction. Even within this category there are different types of WIMPs, including the generally accepted version that is its own antiparticle, leading to annihilation whenever two WIMPs meet, or another one where, just as in ordinary baryonic matter, there are more WIMPs than antiWIMPs. In this model, large sources of gravity like the Sun can net quite a haul of the stuff, and as the weakly interacting particles can pass through the dense interior of the Sun more easily than any ordinary stuff, they can pass heat to the outer layers, increasing thermal conductivity of the Sun. This impacts on a current problem with solar theory, called the Solar Composition Problem in which the calculated thermal conductivity is lower than that required for the outer parts of the Sun to be as hot as they are.

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