Ten billion years ago, well before the formation of our solar system, a gargantuan explosion threw out vast amounts of highly energetic light. A star died in a dazzling supernova, and, though it happened so long ago, the flash was only seen in 2016 and vanished shortly thereafter. But if you missed it then, worry not: We’ll be able to see the blast again.
The supernova was seen with the Hubble Space Telescope by a team of French, American, and Danish researchers. Analysing Hubble infrared data from a particular portion of space, the team realised that three light sources seen in 2016 had disappeared by 2019. As it turned out, all three of those light sources came from a single explosion, but the light took different routes to reach Hubble’s lens. Excitingly, another spot of light from the burst is expected to arrive at Earth in 2037, give or take a couple years, based on the team’s calculations. The research was published today in Nature Astronomy.
The reappearance of the supernova, located in the MRG-M0138 galaxy, is due to a principle called gravitational lensing. When photons (particles of light) are emitted from some cosmic source, they shoot off into space in all directions, travelling in straight lines. But when they pass by a massive object in their transit, the photons may be bent around that structure.
“It is like a train that has to go down into a deep valley and climb back out again,” Steven Rodney, an astronomer at the University of South Carolina and lead author of the recent paper, told Gizmodo in an email. “It gets slowed down on the way in and the way out, which adds about an extra 20 years to its roughly 10-billion-year journey.”
In this case, the light generated by the supernova (named 2016jka, also known as Requiem) was bent around a galaxy cluster named MACS J0138. Some paths around this massive structure are longer than others. That’s why what was an instantaneous spewing of light in the ancient universe arrives at Earth at different times, years apart.
The 2016 sighting included three light sources that appeared in a particular region of space over about 100 days. (“Like a baby photo and two photos of an angsty teenage [supernova],” Rodney said.) Those flashes were gone by 2019, but the team calculated that more light from that ancient explosion will arrive in about 16 years.
Such long-range measures of gravitational lensing could help astrophysicists draw a bead on the perplexing Hubble Constant, the number that describes the rate of the universe’s expansion and that can be measured in a couple different ways, yielding different values. Scientists don’t know quite why the methods give different values, but measuring instances of gravitational lensing like the one at work in the Requiem supernova throw more data at the problem.
“Understanding the structure of the universe is going to be a top priority for the main Earth-based observatories and international space organisations over the next decade,” said Gabriel Brammer, a co-author of the paper and an astrophysicist at the Cosmic Dawn Centre, in a University of Copenhagen press release. “Studies planned for the future will cover much of the sky and are expected to reveal dozens or even hundreds of rare gravitational lenses with supernovae like SN Requiem. Accurate measurements of delays from such sources provide unique and reliable determinations of cosmic expansion and can even help reveal the properties of dark matter and dark energy.”
The upcoming Roman Space Telescope is being launched for this exact purpose: to investigate dark energy by measuring the distance and movement of supernovae that occur from the explosions of white dwarfs, which is what the recent research team suspects Requiem is. The Roman telescope is essentially using these supernovae’s brightnesses to probe the variability of the Hubble Constant and sniff out what’s causing the numbers to fluctuate.
Interestingly, Brammer told Gizmodo that it’s theoretically possible that, by looking at the spot where they expect to see the next flash of light arrive around 2037, scientists could actually see the white dwarf in its pre-supernova state. “We could, in principle, observe that faint little star today,” Brammer said, “though I estimate within a few orders of magnitude that it would take a telescope a trillion times larger than Hubble — a diameter of 2,000 kilometres — to do this.”
That doesn’t sound too practical, but hey, an astrophysicist can dream.