The difficult part of this work is calculating the trajectory of the photons using the physics of general relativity. These equations are notoriously non-linear, so physicist sometimes simplify them by assuming that a system remains constant in the time it takes for light to pass by. The difficulty with black hole binaries is that this assumption does not hold— these objects orbit so rapidly as they approach each other that space-time warps, even during the time it takes for light to pass by.
Andy Bohn(et al.) at Cornell University in Ithaca, New York, reveals how in-spiraling black hole pairs should distort the light field around them. The team has concluded that from large distances, binaries are more or less indistinguishable from single black holes. Only a relatively close observer would be able to see the fascinating detail that they have simulating or one with very high resolving power.
The first observation of much bigger deflections, such as those produced by black holes or black hole pairs, will be something of a triumph for whoever spots them first.
“Einstein, like no other physicist before or after him, demonstrated how the power of human thought alone, used skillfully, can make up for the lack of real experiments. He showed we little humans have the power to deduce equations that govern the natural world by logical conclusion. Thought experiments are common in theoretical physics today. Physicists use them to examine the consequences of a theory beyond that what is measurable with existing technology, but still within the realm of that what is in principle measurable. A thought experiments pushes a theory to its limit and thereby can reveal inconsistencies or novel effects. The rules of the game are that a) relevant is only that what is measurable and b) do not fool yourself. This isn’t as easy as it sounds.” (Credit: Hossenfelder)