The central galaxy of a group of galaxies explodes 100 million years ago. It is precisely due to the activity of a black hole in the center of the galaxy. The black hole swallowed a lot of gas and then exploded. This gas eruption generated around him two large vacuum bubbles, not only in his galaxy but throughout the whole. According to NASA astronomers, the size of these bubbles is representative of the amount of gas that intervened in the black hole.