An article published in the journal “Nature Astronomy” reports a study on a supernova whose glow was distorted and multiplied by a gravitational lens. A team of researchers examined various images captured over the years by the Hubble Space Telescope after three images of the supernova AT 2016jka, dubbed Requiem, were discovered in 2016 archival data. As it’s normal, its brightness faded away until it disappeared but, according to the researchers, a fourth image of that supernova will be visible in 2037, again due to the distortion generated by the gravitational lens produced by the force of gravity of the galaxy cluster MACS J0138.0-2155, or simply MACS J0138.
This is the story of what the collected data indicate is likely a Type Ia supernova. Its story began about 10 billion years ago with the explosion of a white dwarf that reached a critical mass probably after stealing gas from a companion. The glow from this supernova traveled into space and, after about 6 billion years, some of the electromagnetic emissions were deflected in various ways when they passed close to the galaxy cluster MACS J0138. After another 4 billion years, those emissions reached Earth.
The images of this supernova were discovered by Gabe Brammer of the Niels Bohr Institute, University of Copenhagen, starting from the examination of an image captured in 2019 by the Hubble Space Telescope during the REQUIEM (REsolved QUIEscent Magnified Galaxies) program. A comparison with an image captured in 2016 during another Hubble astronomical program showed that in the 2016 image a bright object appeared three times while it was absent in the 2019 image. The image (Joseph DePasquale (STScI)) shows the galaxy cluster MACS J0138 as seen by the Hubble Space Telescope in 2016 and 2019. The supernova Requiem is present in the circles in the 2016 image. The researchers predict that it will appear in 2037 in the position indicated by the yellow circle in the upper left of the 2019 image.
Together with Steve Rodney of the University of South Carolina, Gabe Brammer began a deeper analysis of the system. The prediction of the new appearance of the supernova Requiem derives from the analysis of the gravitational effects of the galaxy cluster MACS J0138 using computer models that describe the various paths taken by the supernova’s light through the various clumps of dark matter present in the cluster. The effects vary in different areas, and this causes deviations in the supernova light that can lead to the delay of several years predicted by the applied models.
The prediction is currently approximate, as the margin of error is a couple of years. The detection will offer useful information for various cosmological researches, as it will provide precise data on the gravitational characteristics of the galaxy cluster MACS J0138 useful for research on dark matter, and Type Ia supernovae are used to measure the expansion rate of the universe therefore more data on the supernova Requiem will increase the accuracy of that measurement.
Exploiting gravitational lenses is becoming more and more common in astronomical research, and the new telescopes that will come into service in the next few years will help those types of research. They will make it possible to identify new supernovae that are very distant and visible only thanks to gravitational lenses, sometimes at different times such as the supernova Requiem.
