Figure 1
APS/Alan Stonebraker

Figure 1: A cartoon of how the Biermann battery process generates a magnetic field. The product of electron temperature and density in a plasma of electrons (white spheres) and protons (not shown) is a quantity called the electron pressure. (In the figure, the pressure is highest at the upper right corner and lowest at the lower left corner.) Electrons flow down this pressure gradient faster than the heavier protons, generating an electromotive force (emf) over a closed contour (white line.) By Faraday’s law, this emf generates a magnetic flux through the surface bounded by the contour. (In this figure, the emf generates a magnetic field out of the page.)