Black holes have been known for quite a long time, but they recently became a field of observational interest especially because numerous observational methods became possible. Although there exists a well-established model of a singular black hole, there are various other alternatives. The major problem is that they mostly predict the same observables in the exterior of the black hole, which is the only testable area. A year ago, a new prediction about observable quantity was published, namely that nonsingular black holes could grow in mass with the universe's expansion. The goal of this master thesis is to test this hypothesis with observational data. To do so we consider X-ray binaries, which are ideal objects to study quantities such as the mass and the age of a black hole. Here we crucially use these two quantities to determine the coupling between mass and the scale factor, performing two different approaches. In the first approach, we check which coupling powers are compatible with black holes formed above the Tolman-Oppenheimer-Volkoff limit. This limit is referred to as the smallest mass of the black hole that can be formed with the collapse of the star at the end of its lifetime. In the second approach we ignore this limit and compare the distribution of masses of young black holes, that couldn't grow much in their short lifetime, with the distribution of masses of black holes at their formation, which can be obtained using the mass and the age of older black holes assuming certain power of coupling. Results using both methods are consistent and show that there is most probably no coupling between the mass of a black hole and the expansion of the universe. We can therefore conclude that our results prefer singular black holes over nonsingular ones.
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