One of the biggest cosmic structures we can see are galaxies, which essentially are vast collections of stars. Our own galaxy is called the Milky Way, and is considered a "barred spiral" shape. There are several types of galaxies, ranging from spiral to elliptical to irregular, and they can change as they come close to other objects or as stars within them age.
Often galaxies have supermassive black holes embedded in the center of their galaxies, which are only visible through the radiation that each black hole emanates as well as through its gravitational interactions with other objects. If the black hole is particularly active, with a lot of material falling into it, it produces immense amounts of radiation. This kind of a galactic object is called a quasar (just one of several types of similar objects.)
Smaller black holes can also form from the gravitational collapse of a gigantic star, which forms a singularity from which nothing can escape — not even light, hence the name of the object. Once believed to be theoretical objects, scientists have found evidence of black holes in the universe. No one is quite sure what lies within a black hole, or what would happen to a person or object who fell into it.
Large groups of galaxies can form in clusters that are groups as large as hundreds or thousands of galaxies bound together gravitationally. Scientists consider these the largest structures in the universe.
