In 2016, the Hubble telescope detected, around a galaxy cluster, three bright spots that vanished after three years. However, it turned out to be a single event: the explosion of a much more distant star (supernova) whose light was distorted.
Now, an international team of astronomers predicts that the same explosion will be observed again in the year 2037. It does not mean that it will happen again, but that its light will reach Earth more than two decades late.
The main cause of this enigmatic phenomenon called “time lag” is the gravity of the aforementioned cluster of galaxies.
According to Einstein’s theory of general relativity, spacetime is deformed by mass. This deformation is gravity and affects any nearby body and particle of light.
Therefore, a cluster of galaxies, which concentrates the mass of billions of stars, generates a gravitational field so powerful that it can easily bend and distort the light particles that arrive from other places in the cosmos.
The star that exploded was located on the edge of a galaxy called MRG-M0138, 10 billion light years from Earth. This galaxy also appears distorted (orange) and reflected several times in the cluster, located 4 billion light years away.
In the center of this cluster more galaxies are concentrated, that is, there is more mass and, therefore, more gravity. And where there is more gravity, the longer it takes for the light to cross.
Near the center of the cluster is an image of the galaxy MRG-M0138, but there is no supernova there yet. Because of its location, they calculate that this light is 21 years behind, so they expect the explosion to be visible in 2037.
“This is the last to arrive because it is like the train that has to go to the deepest part of a valley and leave again. That’s the slowest kind of travel for light, ”explained lead author Steve Rodney, a professor in the Department of Physics and Astronomy at the University of South Carolina at Columbia.
The team of experts, who published the results of this research in the journal Nature Astronomy, also hopes that the occurrence of this time-delayed event, which they have named “SN Requiem”, will allow refining the calculations of the mass of the clusters of galaxies and, ultimately, the rate at which the universe is expanding.