NASA's Hubble telescope spots rare exploding supernova

A supernova that exploded some 10 billion years ago has been captured by Hubble Space Telescope.

And scientists saw this one coming. The Refsdal supernova had been spotted in the galaxy cluster MACS J1149.5+2223. Its reappearance was correctly calculated from different models of the galaxy cluster whose immense gravity is warping the supernova’s light.

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“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,” University of California at Los Angeles’ Tommaso Treu, who led the research on the supernova modeling, said in a statement. “And remarkably all seven models predicted approximately the same time frame for when the new image of the exploding star would appear.”

The supernova has been nicknamed Refsdal in honor of the Norwegian astronomer Sjur Refsdal, who, in 1964, first proposed using time-delayed images from a lensed supernova to study the expansion of the Universe. A supernova is an explosion of a star and also is the largest explosion in space.

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The story of Refsdal began in 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. 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 realized that the galaxy in which it exploded is already known to be a galaxy that is being lensed by the cluster,” University of South Carolina’s Steve Rodney, who was involved in the research, said in a statement. “The supernova's host galaxy appears to us in at least three distinct images caused by the warping mass of the galaxy cluster.”

With so many images of the galaxy, scientists were presented with a rare opportunity.  Since the matter in these clusters is distributed unevenly, the light creating each of these images takes a different path with a different length. As a result, 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.

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Since October, scientists directed Hubble to periodically peer at MACS J1149.5+2223 - hoping to observe Refsdal. Their persistence paid off on Dec. 11.

“Hubble has showcased the modern scientific method at its best,” University of California Berkeley’s Patrick Kelly, who led the researcher of the discovery and supernova’s re-appearance papers and took part in the modeling of it, said in a statement. “Testing predictions through observations provides powerful means of improving our understanding of the cosmos.”