[DrBazza]

I suspect it's the next paragraph - the star orbiting is "normal"

Formation of a black hole is a pretty violent event - a supernova. Which sometimes ejects a companion star, and would certainly strip it of mass and change its chemical composition.

(edit) One other thing that makes a black hole 'special' is if they're really light (possibly formed via two neutron stars colliding).

> The fact that the star is very similar to the Sun is also quite special. It is different from the companions of most other known black holes (see the location of the newly found Gaia-BH1 with respect to the other known black holes as highlighted in Figure 1). If this system also contains planets, like a large fraction of solar-type stars do, it would be an even more interesting object for further studies!

https://en.wikipedia.org/wiki/Black_hole#Formation_and_evolu...