The Nuclear Spectroscopic Telescope Array (NuSTAR), a small X-ray space telescope used by NASA, (The National Aeronautics and Space Administration) made an amazing observation: a strange blue and green light that disappeared a few days later. Until now, scientists did not know why it appeared, but a study published in the Astrophysical Journal may well provide a likely explanation for this surprising light.The main role of NuSTAR is to study the sources of X-ray emissions: in concrete terms, the telescope is responsible for finding and assessing the mass of black holes and supernovas. The strange green light was spotted not only by NuStar but also by NASA's Chandra X-ray Observatory ten days after it was first spotted.'Ten days is a really short amount of time for such a bright object to appear,' explained Hannah Earnshaw, a researcher at Caltech (California Institute of Technology, USA). 'Usually, with NuSTAR, we observe more gradual changes over time and we don’t often observe a source multiple times in quick succession. In this instance, we were fortunate to catch a source changing extremely quickly, which is very exciting.'A black hole devouring another star?According to the study, it's possible that this light is coming from a black hole 'devouring' another star. When an object gets too close to a black hole, it can be shredded by gravity, and the debris ends up in orbit near the black hole.Debris near the inner edge of the black hole moves so fast that it heats up to about 5,000°C (about the temperature of the Sun) and gives off X-rays. This could explain why NuSTAR has spotted a green light source. 'This result is a step towards understanding some of the rarer and more extreme cases in which matter accretes onto black holes or neutron stars,' said Hannah Earnshaw in a release.