But this case, reported Thursday in Science, is much more special: Because of the lensing effect of a massive galaxy located between this supernova and the telescope imaging it, the same explosion showed up four times around the galaxy. This formation is called an Einstein Cross. Einstein first predicted the phenomenon of gravitational lensing (a result of his theory of relativity) about a century ago.
Astronomers have seen Einstein Crosses made by galaxies and black holes before, but this is the first time they've seen a supernova jump into the shot.
In this case, the supernova -- which is 9 billion light years away -- would be too faint to be visible from Earth with just one galaxy magnifying it. As luck would have it, the explosions ended up being lensed twice: A massive cluster of galaxies bent the light of the supernova, probably producing three of the images, and one of those was caught again and bent by a final galaxy. In total, the light of the explosion is magnified by 20 times.
"It really threw me for a loop when I spotted the four images surrounding the galaxy - it was a complete surprise," study author Patrick Kelly of the University of California said in a statement. Kelly was looking to find the small, distant supernovas that can be magnified by gravitational lenses, but this new Einstein Cross provides opportunities of its own.
"Basically, we get to see the supernova four times and measure the time delays between its arrival in the different images, hopefully learning something about the supernova and the kind of star it exploded from, as well as about the gravitational lenses," Kelly said.