The mystery of an incredibly bright supernova first discovered in 2010 has finally been explained.
A new study has revealed the PS1-10afx supernova, which shines around 100 billion times brighter than the Sun, is the light from a type of star explosion which was maginified by a cosmic lens.
It was originally believed that PS1-10afx was the result of a new kind of stellar explosion. However, an international group of astronomers has deduced that another galaxy positioned between Earth and the supernova acted as a 'gravitational lens' - which magnified the brightness of the supernova by warping space-time.
A gravitational lens refers to a series of plates between a distant object and an observer, which is capable of bending the light from the source as it travels towards the observer.
PS1-10afx is a type of supernova located around 9 billion light-years from Earth. The new supernova finding has also provided researchers with an insight into the expansion of the universe.
It is a 1a supernova, dubbed "standard candles", as they can be used to measure distances in space.
A supernova is a stellar explosion that causes a burst of radiation that often briefly outshines an entire galaxy, before fading from view over a period of weeks. The explosion forces out the majority of a star's material with a velocity of up to 30,000km/s.
The luminocity of PS1-10afx is what drew astronomers to differentiate the supernova from other stellar explosions. It was discovered four years ago by the Panoramic Survey Telescope & Rapid Response System 1 (PanSTARRS1) in Hawaii.
The team collected data from PS1-10afx after the brightness from the explosion had faded. They discovered two sets of emission lines from the supernova - evidence of the gravitational lens in the foreground.
Dr Robert Quimby, of the University of Tokyo's Kavli Institute, explained to BBC News: "PS1-10afx was different in just about every way. It evolved too fast, its host galaxy is too big, and it was way, way too red. We had no direct evidence for the lens."
Quimby's team used the Keck telescope in Hawaii to find the lens. He added: "Looking at the spectra we could check to see if there was light coming from two sources at two separate distances, which is what we found. There is a second, previously unidentified galaxy, hiding in plain sight in front of the supernova."
The lensing galaxy's light was obscured by the brightness of the supernova and its host galaxy.
As PS1-10afx is the first supernova of its kind to be magnified by gravitational lensing, understanding the phenomenon could help scientists learn more about the expansion of the cosmos. It is known to be increased by dark energy, a hypothetical form of energy believed to make up 75% of the universe.
"Each image will arrive at a different time with the exact delay dependent on how fast the Universe is expanding. In principle, measuring this delay provides a direct way to measure cosmic expansion," Dr Quimby explained.
Robert Kirshner, an astronomer at the Harvard-Smithsonian Center for Astrophysics, told Space.com: "The next step is to get a really good Hubble Space Telescope image of the host galaxy, and see if you can pick out the lens galaxy, which must be superposed on it."
The new study was published in the journal Science.