Yep, the answer is a bolt of lightning, which can reach temperatures of roughly 30,000 kelvins (53,540 degrees Fahrenheit). The sun, on the other hand, is eclipsed in this case - its surface temperature is just 6,000 kelvins (10,340 degrees Fahrenheit).
Though it is said that Balerion's fire was so intense it burned black, really the hottest of flames is white. Assuming his flame was in fact white hot, as all available art seems to indicate, it burns with a minimum temperature of around 2800 degrees Fahrenheit.
