What if the Milky Way’s central “black hole” isn’t a black hole at all? A new model proposes that an ultra-dense dark matter core could mimic its gravitational pull.

Through nine questions, from the merely intriguing to the existential and utterly bonkers, this special feature confronts the staggering vastness of the cosmos and our place in it.

For decades, scientists have been observing how galaxies spin and move throughout the universe. Gravity acts on stars and galaxies, in the same way it keeps you from floating off into space. Heavier ...