Massive stars end their lives in a colossal explosion, which Fritz Zwicky called a supernova. The core crushes down into a black hole or a neutron star.
Light from a distant galaxy travels across the universe, passing through vast clumps of dark and ordinary matter. Their gravity slightly bends the path of the rays, like a river's current flowing around invisible boulders. In images, this shows up as a barely noticeable elongation of galaxy shapes, as if they were stretched on an invisible frame.