1. Sagittarius A* is the supermassive black hole at the heart of our galaxy, 4 million times as hefty as the Sun. It is calm compared with the black holes in many active galaxies, but it may have been much more active in the past.2. The Arches Cluster is the densest star cluster in the galaxy. Winds blowing from hot, newborn stars collide at high speeds here, creating the observed x-rays.
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