X-rays from the Sun
Remember - for thermal radiation - the frequency of light (the energy of each photon) is proportional to the temperature of the emitter:
Human body = 300 K Þ 10 microns, or 100,000 Å (infrared)
Sun, light bulb filament = 6000 K Þ 5000 Å (visible, yellow)
Hot star’s surface = 40,000 K Þ 750 Å (far ultraviolet)
Really hot plasma = 5,000,000 K Þ 6 Å (X-ray)
*don’t forget that thermal emitters give off photons with a range of wavelengths; those listed above represent the peak of the distribution