A team of astrophysicists and mathematicians hailing from the University of Southampton, the University of Cambridge, and Institut de Ciències del Cosmos Universitat de Barcelona has put forward an intriguing idea. They propose that certain combinations of black holes, separated by the expansive forces of the cosmos, might appear as a single black hole with equal mass.

Their study, which has been published in the journal Physical Review Letters, delves into the rationale behind this notion and why it does not defy Einstein’s theory of general relativity, despite established theorems suggesting that such binary black hole systems couldn’t exist.

Traditionally, Einstein’s theory has yielded a single solution concerning black holes, implying that all black holes should be identical. Nevertheless, recent research has unveiled exceptions that don’t contradict this singular equation. This typically holds true in scenarios where no other energy influences the system, leading to a state of equilibrium, meaning no motion or rotation.

However, certain situations challenge this paradigm. For instance, when a black hole consumes charged matter, triggering a surrounding field, it departs from the single formula but adheres to other theorems.

Another intriguing scenario is when two black holes repel each other with precisely the same force as their gravitational attraction, resulting in them existing at a fixed distance from each other. Under these conditions, these two black holes would be indistinguishable from a single one, allowing them to be treated as a unified entity within the confines of general relativity’s single solution formula.

Now, this research team has uncovered a similar situation involving a pair of black holes. These black holes are both drawn together by gravity and simultaneously pushed apart by cosmic expansion in equal measure. As a result, they remain in a state of permanent stasis. Through complex mathematical analysis involving black holes with opposing spins, the researchers have shown that such an arrangement could theoretically exist. Importantly, it does not contradict general relativity, as it can be regarded as a single entity, albeit for different reasons.

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