Suppose the surface temperature of the Sun were about 18,000 K, rather than 6,00

From the first rule of thermal radiation, we know that tripling the temperature of an object increases the amount of thermal radiation it emits per unit area by a factor of 3^4 = 81.  Thus, increasing the surface temperature of the Sun from 6,000 K to 18,000 K would increase its thermal radiation by a factor of 81. The higher temperature of the Sun would shift the peak of its thermal radiation spectrum from its current place in the visible light region into the ultraviolet. The hotter Sun would emit more energy at all wavelengths, with the greatest output coming in the ultraviolet.