Astronomers observe predicted supernova explosion

The left-hand image displays the location of the Refstal supernova in a larger context, while the image on the top right shows a Hubble search for the Refstal supernova prior to the occurrence – the bottom right image displays the location of the now-visible supernova(Credit: NASA & ESA and P. Kelly (University of California, Berkeley))

For the first time, a team of astronomers has successfully made observations of a predicted supernova. The enormous cosmic explosion, nicknamed Refsdal, is believed to have occurred roughly 10 billion years ago, and owes its foreshadowing to a rare astronomical phenomenon known as an Einstein Cross, which led to the recent spotting which took place on Dec. 11th.

Refsdal was originally discovered in November 2014, with the aid of a powerful gravitational lensing effect created by the galaxy cluster MACS J1149.5+2223. Surprisingly, the scientists observed four images of the supernova instead of one, due to a rare occurrence called an Einstein Cross.

Because dark and visible matter are unevenly distributed throughout large structures such as MACS J1149.5+2223, the light from the lensed supernova that composes the four images observed by the Hubble Space Telescope, travels divergent routes. The paths taken by the light will be longer or shorter than others depending on the strength of the lensing effect on their path, meaning that the instances of the supernova become visible to Earth-based observatories at different times.

This cosmic quirk has granted astronomers a rare opportunity to validate their understanding of mass distribution on large structures such as MACS J1149.5+2223. By employing a number of sophisticated computer models based on our best understanding of matter distribution, astronomers predicted that first detection of Refsdal would occur before the end of 2015.

The appearance of the supernova at the correct time represents a promising sign as to the validity of current mass distribution models.

"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," states Tommaso Treu, lead author of the modelling comparison paper, from the University of California, Los Angeles. "And remarkably all seven models predicted approximately the same time frame for when the new image of the exploding star would appear".

Furthermore, according to the astronomers, the Dec. 11 sighting was in fact the third appearance of the cosmic explosion. If the computer models used to forecast the recent return of Refsdal are accurate, the supernova first appeared in our skies in 1998, but was unobserved by contemporary telescopes.

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