Hubble captures images of first-ever predicted supernova

Scientists, using Hubble Space Telescope, have captured the image of the first-ever predicted supernova in action, which exploded nearly 10 billion years ago.

The supernova, nicknamed Refsdal, has been spotted in the galaxy cluster MACS J1149.5+2223. The finding served as a unique opportunity for astronomers to test their models of how mass - especially that of mysterious dark matter - is distributed within this galaxy cluster, researchers said.

Many stars end their lives with a with a bang, but only a few of these stellar explosions have been caught in the act.

On December 11 this year, astronomers not only imaged a supernova in action, but saw it when and where they had predicted it would be.

While the light from the cluster has taken about five billion years to reach us, the supernova itself exploded much earlier, nearly 10 billion years ago.

The reappearance of the Refsdal supernova was calculated from different models of the galaxy cluster whose immense gravity is warping the supernova's light.

Last year, 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.

The cosmic optical illusion was due to the mass of a single galaxy within the cluster warping and magnifying the light from the distant stellar explosion in a process 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," said study co-author Steve Rodney, 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," said Rodney.

These multiple images of the galaxy presented a rare opportunity. As the matter in the cluster - both dark and visible - is distributed unevenly, the light creating each of these images takes a different path with a different length.

Therefore the images of the host galaxy of the supernova are visible at different times.
Using other lensed galaxies within the cluster and combining them with the discovery of the Einstein Cross event in 2014, astronomers were able to make precise predictions for the reappearance of the supernova.

Their calculations also indicated that the supernova appeared once before in a third image of the host galaxy in 1998 - an event not observed by any telescope. To make these predictions they had to use some very sophisticated modelling techniques.

"We used seven different models of the cluster to calculate when and where the supernova was going to appear in the future," said study lead author Tommaso Treu, from the University of California at Los Angeles.