Black holes are the most extraordinary prediction of Einstein’s Theory of Relativity. When a star that is too massive to form a neutron star dies, it simply collapses to nothing, leaving only its gravitational field behind. The gravitational field is so strong that the material of the star is actually cut off from the rest of the Universe by a surface of no return, the event horizon. The gravitational field that remains is absolutely simple.
Everything about it can be described by an equation that depends on just the mass and spin of whatever remains beyond the horizon. All of the other details of the original dying star do not matter. These two numbers tell us all that everything about the black hole itself, and Einstein’s theories make precise predictions about how material and light will travel near the black hole. Colibrì will test those predictions with unrivalled accuracy.