Sun material was pretty simply mix of the fractals maps (mostly noise and cellular).
Sun flames was created with Particle Flow as simple trails coming from sun. There was 6 particle layers to get different scale of flames (bigger, thinner, some very very small just to fill sun surface). Particles was rendered as simple lines with just one color, but to fill dotness gap there must be A LOT of particles (milions). To render such amount of dots I was used Krakatoa render from Prime Focus (Frantic Films).
And a truly magic was created by compositing everything together. I work with eyeon Fusion, but it can be done in any software, just if you know how to draw it with Photoshop, probably you will get job done in any software too ;)
Best Luck!