Double Vision! These ‘Twin’ Quasars Are Actually The Same Thing

The quasar QSO 0957+561 appears twice in the center of this image due to a phenomenon known as gravitational lensing, which takes place when light bends around another (massive) object. Credit: ESA/NASA

Optical illusions are awesome. In the center of this image are what appear to be two quasars (or galaxies with huge black holes). In fact, however, it’s the same quasar seen twice. So what’s going on?

QSO 0957+561, also called the “Twin Quasar”, was first spotted in 1979. It lies almost 14 billion light-years from Earth (making it about as old as the Universe itself). Initially, astronomers thought it was indeed two objects, but the distances and characteristics of the twins were too similar.

We “see” the quasar twice because of a ginormous galaxy called YGKOW G1. Its immense gravitational mass is bending the light of the quasar so that it appears twice from our perspective. This phenomenon is called “gravitational lensing”, and it turned out in 1979 that QSO 0957+561 was the first object ever confirmed to experience that. (You can read the original Nature research paper here.)

While the discovery is decades old, it’s still fun to turn telescopes in that direction once in a while to spot the illusion. This particular image is a new one from the Hubble Space Telescope.

Source: NASA