Two objects are clearly visible in this Hubble image, shining brightly side-by-side. When they were first discovered in 1979, the objects were thought to be separate objects, but astronomers soon realized that these twins are too identical! They are close together, lie at the same distance from us, and have surprisingly similar properties. The reason they are so similar is not some bizarre coincidence. They are in fact the same object. They are a double quasar known as QSO 0957+561 (aka the Twin Quasar). It is among the oldest object we can see, just under 14 billion light-years from Earth. Quasars are the intensely powerful centers of distant galaxies.
So, do we see this quasar twice?
Directly in our line of sight about 4 billion light-years from Earth is the huge galaxy YGKOW G1. This galaxy is gravitational lens, an object with a mass so great that it can bend the light from objects lying behind it. This phenomenon not only allows us to see objects that would otherwise be too remote, but also, in some instances, it allows us to see them twice. Along with the cluster of galaxies in which it resides, YGKOW G1 exerts an enormous gravitational force which affects the very space it sits in, warping and bending the environment and producing bizarre effects, such as this quasar double image.
Gravitational lensing is evidence for Einstein’s theory of general relativity. This theory had identified gravitational lensing as one of its observable effects, but until the discovery of these quasar “twins,” no such lensing had been observed since the idea was proposed in 1936.
Image Credit: NASA