Scientific Controversies: Black Holes

Black holes are gloriously weird. Formed as the death state of heavy stars, they can be as small as cities or as big as solar systems. Our own Milky Way galaxy is anchored at its center by a black hole four million times the mass of our sun but only 20 sun widths across. The rest of our galaxy could harbor billions of city-sized black holes. There are hundreds of billions of galaxies in the observable universe, each one replete with billions of stellar mass black holes and each one probably the home to one supermassive black hole. Beyond the oddity of black holes, they may play an essential role in sculpting galaxies and the universe on the largest scales. Black holes may have carved a world that we could live in.