Are there any known non-rotating black holes

[Lucas_Jackson]

I was reading an interesting article on photon spheres…

A photon sphere is a spherical region just outside a black hole’s event horizon where gravity is so intense that light (photons) is forced to travel in circular orbits. Because spacetime is extremely warped, emitted light loops around the black hole rather than traveling in straight lines or escaping into deep space.

And there was a mention of non-rotating black holes. A first thought is that conservation of angular momentum would prevent them. Googling around a bit I found this opinion…

Implausible and unlikely. But not entirely impossible, because angular momentum is conserved. So two equal but opposite black holes (or neutron stars) can merge and negate each other’s spin (or charge) to an immeasurably low level (even if not absolute zero). And as statistically improbable as that is, considering the sheer number of stellar black holes (and neutron stars) in the observable universe, it may actually be inevitable (within a certain degree of measurement)

My factual questions:

1. Have we detected a non-rotating black hole?
2. Would we even be able to know (since black holes are all but invisible)
3. Do all black holes have photon spheres?