The Sunspots appear darker than the other regions because they are cooler; and I know that according the Babcock model, the Sunspots are places where the tangled magnetic fields burst out through the Sun's surface. How does these bursting magnetic field lower the Sun's surface temperature?

I found a good explaination:
Collins, G. W. (2021). Sunspots. In K. H. Nemeh & J. L. Longe (Eds.), The Gale Encyclopedia of Science (6th ed., Vol. 7, pp. 4326-4329). Gale. https://link.gale.com/apps/doc/CX8124402391/CIC?u=utoronto_main&sid=bookmark-CIC&xid=d939e1ba


1 Answer 1


As I discuss in https://physics.stackexchange.com/a/415248/59023 and https://physics.stackexchange.com/a/708183/59023, a sunspot is a pressure-balance structure. The total pressure in a collisionally mediated plasma includes the thermal and magnetic pressures. Since the regions involved in generating sunspots arise from the enhanced magnetic fields of flux ropes rising to the photospheric surface, we know that the magnetic pressure is high. We assume the thermal pressure is given by: $$ P = n \ k_{B} \ T \tag{0} $$ where $n$ is the number density [number per unit volume], $k_{B}$ is the Boltzmann constant, and $T$ is the temperature.

Since this is a collisionally mediated system, the density inside and outside these structures will roughly remain the same but the temperature can vary. To remain in pressure balance (i.e., total pressure outside equals total pressure inside), the temperature must then drop to accomodate the higher magnetic pressure.


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