A flare erupted from our Milky Way’s center some 3.5 million years ago. While Earth wouldn’t be in any danger if it happened today, the the light would be clearly visible. (Credit: James Josephides/ASTRO 3D)

Astronomers believe supermassive black holes probably lurk in the centers of most large galaxies. These gargantuan black holes can gather swirling disks of material around them as their gravity attracts stars and gases. In some cases, these disks can emit vast amounts of light and even s