The universe is an endless expanse of mystery, majesty and mind-blowing spectacle. So why, a few years from now, is the cosmos airing a "rerun" of a supernova explosion that we already watched in 2016?
Known as Supernova Requiem, the faint glint of an ancient, 10 billion-year-old explosion is expected to reappear in the sky sometime around the year 2037 — even after the same light source already smiled for NASA's Hubble Space Telescope three times in 2016.
The reason for this cosmic rerun doesn't have anything to do with the supernova itself, research published Sept. 13 in the journal Nature Astronomy suggests, but with the gargantuan cluster of galaxies that the nova's light has to pass by on its way to Earth.
"Whenever some light passes near a very massive object, like a galaxy or galaxy cluster, the warping of space-time that Einstein's theory of general relativity tells us is present for any mass, delays the travel of light around that mass," lead study author Steve Rodney, an assistant professor at the University of South Carolina in Columbia, said in a statement.
This phenomenon is called gravitational lensing. The effect occurs when a gravitationally massive object warps or lenses the light of distant stars and galaxies behind it — sometimes magnifying the light of distant objects, and sometimes distorting it. In the case of Supernova Requiem, the large galaxy cluster MACS J0138 is causing the stellar explosion's light to brighten, multiply and split into several different images, seemingly appearing at different points in the sky at different times, the researchers said.
The first time astronomers spotted Requiem in a 2016 Hubble image of the MACS galaxy cluster, the supernova appeared simultaneously in three different spots around the galaxy cluster's edge. The three different images varied in brightness and color, suggesting they showed three different phases of the supernova as it dimmed and cooled over time, the researchers said.
In a follow-up image of the cluster taken in 2019, all three points of light had disappeared entirely, confirming that they were all mirror images of the same distant light source. Researchers have since learned that the light originates from an ancient supernova located about 10 billion light-years from Earth, meaning the star in question lived and died within the first 4 billion years after the Big Bang.
But a closer look at the MACS cluster revealed that Supernova Requiem's magic show wasn't over yet; light traveling through the exact center of the galaxy cluster is still being pinballed around by the cluster's intense gravity, and it has yet to appear on the Earth-facing side.
In their new study, the researchers used a computer model to map the galaxy cluster's dark matter — the mysterious, invisible substance that makes up a majority of the matter in the universe and serves as the glue that binds large galaxies together. With this map, the team predicted the various pathways that light from Supernova Requiem could take through the galaxy cluster on its way to Earth, and how dark matter might influence its arrival.
The researchers calculated that light traveling through the center of the cluster, where dark matter is densest, should appear in the sky over Earth in the year 2037, give or take two years. (The supernova may also appear a fifth time, in the year 2042, but that light will be so dim that astronomers may not be able to see it at all, the team added).
That's an "extraordinarily long" delay between the light's first appearance and its last, Rodney said — the longest ever observed from a multiply-lensed supernova.
Once the long-awaited nova reappears in the sky, astronomers will be able to measure the precise time difference between all four supernova images, allowing them to better understand the gravitationally warped path that the dying star's light had to traverse. Ultimately, this could give the researchers more clues about the nature of dark matter, the authors concluded. So, settle in and don't touch that dial; the reappearance of Supernova Requiem is one rerun worth watching.
Originally published on Live Science.
