General Relativity IV

The Great Square of Pegasus stands high in the south as night falls — four moderately bright stars that outline the body of the flying horse. Another square stands to its lower right. It’s billions of light-years away, so it takes a big telescope to pick it out. But it’s an amazing confirmation of general relativity — Albert Einstein’s theory of gravity.
The theory says that gravity is a “warp” in space and time caused by the presence of matter. Larger, denser concentrations of matter create a stronger warp. These objects can “bend” light around them, creating optical illusions.
And that’s where the Einstein Cross comes in. It consists of a square of four equally bright points of light, with a fainter fifth pinpoint in the middle. The center light is a galaxy. The four points around it are all projections of a quasar that’s far behind the galaxy. The galaxy’s gravity acts as a lens. It “bends” the quasar’s light around the galaxy, projecting it as four separate images.
This “gravit