Question

2) The magnetic field in the center of a sunspot has strength B = 2000 Gauss (cgs units).

2a) Calculate the magnetic pressure, P_m, at this location and compare it to the gas, P_g ≈ 5 × 10^5 dynes/cm^2 at the base of the Sun’s photosphere.

2b) How does this pressure difference lead to sunspots being cooler and darker than their surroundings?

Answer 1

2.

(a)

(b) Sunspots are cooler and darker because the intense magnetic field Inhibit the flow of plasma and thus ceases the heat to flow due to convection. It allows them to cool radiatively. Since the radiation spectra of the sun is roughly close to the Planck function and thus as the sunspots are cooler the Planck function is lower than the surroundings. As Planck function is lower their brightness is smaller than the surroundings and thus appears as darker than the surroundings.

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