This supernova exploded nearly 10 billion years ago.
Most stars end their life in a bang, however, few of them are ever caught red-handed. When they are spotted, it is mainly due to pure luck. Until now.
On December 11, 2015 astronomers using the NASA/ESA Hubble Space Telescope not only predicted the supernova explosion, they also saw it when and where they had predicted it would be.
The supernova, named Refsdal, was spotted in the galaxy cluster MACS J1149.5+2223. The light from this galaxy cluster took five billion years to reach us, however, the supernova itself exploded nearly 10 billion years ago.
So how did scientists know when and where to point Hubble? It goes back all the way to November 2014 when scientists spotted four separate images of the supernova in a rare arrangement known as an Einstein Cross around a galaxy within MACS J1149.5+2223. An Einstein Cross is a cosmic optical illusion caused by a galaxy that warps and magnifies the light from a stellar explosion — known as gravitational lensing.
"While studying the supernova, we realised that the galaxy in which it exploded is already known to be a galaxy that is being lensed by the cluster," explained Steve Rodney, co-author, from the University of South Carolina. "The supernova's host galaxy appears to us in at least three distinct images caused by the warping mass of the galaxy cluster."
Using other lensed galaxies within the cluster and combining them will the Einstein Cross, astronomers were able to make predictions for the reappearance of the supernova using advanced modeling techniques.
“We used seven different models of the cluster to calculate when and where the supernova was going to appear in the future. It was a huge effort from the community to gather the necessary input data using Hubble, VLT-MUSE, and Keck and to construct the lens models,” said Tommaso Treu, lead author of the modeling comparison paper, from the University of California at Los Angeles, USA. “And remarkably all seven models predicted approximately the same time frame for when the new image of the exploding star would appear.”
So since the end of October, Hubble has been periodically looking at MACS J1149.5+2223, in hopes of spotting the explosion and proving the models correct. Astronomers got their wish on December 11. “Hubble has showcased the modern scientific method at its best,” said Patrick Kelly, lead author of the discovery and re-appearance papers and co-author of the modeling comparison paper from the University of California Berkeley. “Testing predictions through observations provides powerful means of improving our understanding of the cosmos.”
Astronomers are now looking to use these newly tested models to determine how dark matter is distributed within this galaxy cluster.
If you are interested in reading about the many different ways a star can die, check out this informative article.