SUPERNOVA PREDICTION LEADS TO IMAGE

WE GOT ONE! Hubble spotted these four projections
of the same supernova whose light is warped
by a galaxy cluster. In December, a fifth appeared

On December 11, astronomers used the Hubble Space Telescope to image for the first time a supernova at the place and time they predicted it would appear.

The project began after the Grism Lens Amplified Survey from Space and Hubble’s Frontier Fields program captured the distant galaxy cluster MACS J1149+2223, creating multiple images of a supernova around a large elliptical galaxy. Astronomers refer to this process as gravitational lensing. The cluster lies some 5 billion light-years from Earth, and the supernova is roughly twice as far away

“It really threw me for a loop when I spotted the four images surrounding the galaxy — it was a complete surprise,” said Patrick Kelly of the University of California, Berkeley, lead author on the supernova discovery paper.

The real surprise came when the astronomers predicted — and then captured — a fifth image of the supernova. This was possible because the matter within the galaxy cluster has an uneven distribution, so the supernova’s light can take different paths to our instruments.

“We used seven different models of the cluster to calculate when and where the supernova was going to appear in the future,” explains Tommaso Treu, lead author of the modeling comparison paper, from the University of California at Los Angeles, “and remarkably all predicted approximately the same time frame for when the exploding star would appear.”

After the predictions were in hand, the team used Hubble starting at the end of October to monitor the galaxy cluster periodically. And on December 11, the supernova reappeared as a fifth gravitationally lensed image.

The astronomers have nicknamed the supernova “Refsdal” in honor of Norwegian astrophysicist Sjur Refsdal, who did pioneering work on how gravitational lensing could help scientists study the universe’s expansion.