At present, we probably do not have the ability to detect these small changes in phenomena. However, this could 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. The team (four researchers based in Shanghai and CERN) therefore decided to repeat an analysis carried out shortly before the Event Horizon Telescope was commissioned, and to determine whether the next-generation hardware might be able to detect features in the environment around the black hole that could distinguish between different theorized versions of gravity.
Theorists have been busy, and there are many potential solutions to replace general relativity. So, rather than going through the list, they used a gravity model (the parametric Konoplya–Rezzolla–Zhidenko metric) that is not specific to any given hypothesis. Instead, it allows some of its parameters to be changed, allowing the team to vary the behavior of gravity within certain limits. To get an idea of what kind of 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 general relativity’s standard version of the event horizon.
Small but clear differences
Using these five versions of gravity, they model the three-dimensional environment near the event horizon using hydrodynamic simulations, including the incoming matter, the magnetic fields it produces, and the jets of matter powered by those magnetic fields.
The results resemble the type of images produced by the Event Horizon Telescope. These include a bright ring with substantial asymmetry, one side of which is significantly brighter due to the rotation of the black hole. And although the differences are subtle between all variations of gravity, they exist. An extreme version produced the smallest but brightest ring; another had reduced contrast between the light and dark side of the ring. There were also differences between the width of the jets produced in these models.
