Current questions in cutting-edge black hole resea

Friends, thought of throwing up a few current open questions/problems in cutting-edge black hole research and seeing what you all think of them.


Firstly, let me define black holes:

Black holes are predicted by general relativity to be formed whenever sufficient mass is compressed into a small enough volume. A black hole is defined as a region of spacetime that cannot communicate with the external universe. The boundary of this region is called the surface of the black hole, or the
event horizon.


Secondly, let me define the three general categories into which black holes are classified:

1) Stellar-mass black holes: These are formed by the gravitational collpase of stars, post-supernova. They are undetectable unless they orbit another start in a binary system.

2) Supermassive black holes: These are believed to be present at the centers of most galaxies. They typically have masses of the order of millions of times our Sun's mass.

3) Micro black holes: These are physically the most intriguing type of black hole, they are believed to have formed in the very early universe due to quantum fluctuations in the primordial brew.


Some current open questions:

1) Do black holes have internal structure?
2) Do black holes retain any memory (mass/energy/charge/spin/particle type) of the matter they swallow?
3) Do stationary black holes emit gravitational waves?
4) Can black holes form quantized bound states?
5) Can sub-Planck mass micro black holes exist?
6) What happened to the micro black holes produced in the early universe? Did they evaporate; or are they still around in some form?
7) Is there any link between black holes and dark matter?
8) Is there any link between black holes and dark energy?
9) Can black holes have multiple singularities?
10) Can Hawking radiation emitted by decaying black holes give rist to Untra High Energy Cosmic Rays?


Hope this gives some food for thought. Would love to see your ideas/thoughts/comments!