Black Holes Explained
On April 10, 2019, the world saw the first picture of a black hole ever taken courtesy of the Event Horizon Telescope team.
This is a picture of the supermassive black hole at the center of the Messier 87 galaxy, about 55 million light years away from Earth. It has tentatively been named Pōwehi, a Hawaiian phrase meaning “embellished dark source of unending creation.”
So black holes are in the news again, and that means that you may have many questions about what you’ve heard: What exactly are black holes, where do they come from, how do they work, and why are they so important?
Spacetime and how black holes work
Black holes are predicted by general relativity. To understand them, we need to start by understanding spacetime and its relationship with gravity.
In physics, we always make measurements with respect to a particular reference frame. A reference frame can be thought of as a coordinate system whose origin is prescribed to move in space in a particular way. For example, we can speak of a reference frame called S in which a person standing at a train station appears to not be moving, and we can compare this to a reference frame called S′ in which the train is not moving.
