BERKELEY, Calif., Dec. 18 (UPI) -- A supernova that happened 9.3 billion years ago was recently replayed for astronomers on Earth two times -- each vision separated by 13 months.
The bit of astronomical déjà vu was made possible by a unique gravitational trick described by Einstein's theory of general relativity. As spacetime approaches objects such as stars or galaxy, it bends and slows. The gravitational forces of large spinning objects like galaxies, also cause light to bend.
These realities affected the 9.3 billion-year journey of light as it traveled from the ancient explosion of a massive star called Refsdal -- found near the edge of the observable universe -- to the lens of the Hubble Space Telescope.
Roughly halfway through its trek from the edge of the universe to Earth, the light encountered a massive galaxy cluster called MACS J1149.5+2223, lying some 5 billion light-years away. The light that traveled directly through cluster's center was delayed by more than a year.
Astronomers first saw the supernova on November 10, 2014. One of the galaxies from the cluster split the light into a quadrant of four images -- a phenomenon known as the Einstein Cross. It was the first time a gravitational lens allowed astronomers to see multiple simultaneous images of a supernova.
The gravitational lens also magnified the supernova light, making it possible to detect what would have otherwise been too faint to pick out among the cosmological noise.
Based on relativity models, researchers predicted the supernova would be replayed several months later, and again several months after that. They also estimated that an initial burst of light from the supernova -- light that took the longest but fastest route around the outer edge of the cluster -- likely arrived in 1998 when no one was looking.
"We used seven different models of the cluster to calculate when and where the supernova was going to appear in the future," explained researcher Tommaso Treu. "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."
As predicted, the replay happened 13 months later. Researchers say the replay confirms relativity theories.
"Hubble has showcased the modern scientific method at its best," Patrick Kelly, astronomer at the University of California Berkeley, said in a press release. "Testing predictions through observations provides powerful means of improving our understanding of the cosmos."