Right now we probably don't have the ability to detect these small changes in phenomena. However, that may change as a next-generation version of the Event Horizon Telescope is being considered, as well as a space telescope that would operate on similar principles. So the team (four researchers from Shanghai and CERN) decided to repeat the analysis they carried out shortly before the Event Horizon telescope went into operation, and see whether next-generation equipment could pick up features of the environment around the black hole that might distinguish between different theoretical versions of gravity.
Theorists have been busy, and there are many potential replacements for general relativity. So instead of working through the list, they used a gravity model (the Hemp-Rezzolla-Zhidenko parametric metric), which is not specific to any particular hypothesis. Instead, it allows some of its parameters to be changed, allowing the team to change the behavior of gravity within certain limits. To understand what differences might be present, the researchers swapped two different parameters between zero and one, giving them four different options. These results were compared to the Kerr metric, which is the standard version of the event horizon of general relativity.
Small but obvious differences
Using these five versions of gravity, they simulate the three-dimensional environment near the event horizon using fluid dynamics simulations, including falling matter, the magnetic fields it creates, and the jets of matter that feed those magnetic fields.
The results resemble images taken by the Event Horizon Telescope. These include a bright ring with significant asymmetry, in which one side is significantly brighter due to the rotation of the black hole. And although the differences between all gravity options are small, they exist. One extreme version had the smallest but brightest ring; another had the contrast between the bright and dim sides of the ring reduced. There were also differences in the width of the jets produced in these models.
