Labels:text | line | screenshot | font | diagram | plot | number OCR: 1000- 100- OBSERVED GAMMA RAY BACKGROUND 10- 1 0.1| PREDICTED GAMMA RAY NUMBER OF PHOTONS BACKGROUND FROM 300 PRIMORDIAL BLACK HOLES 0.01 PER CUBIC LIGHT YEAR 0. 1 10 100 1000 PHOTON ENERGY (MeV) FIGURE 7.5