Dark Matter isn’t made up of baryons unlike normal matter, which is a combination of protons and neutrons. Dark matter doesn’t interact with electromagnetic forces. it doesn’t absorb or emit light, it doesn’t even reflect it like normal matter. The only way it can be detected is through its gravitational pull on normal matter.
Anything can become a black hole if you compress it to a small enough point, this is known as Schwarzchild radius, or gravitational radius. For example, if you shrunk The Earth to the size of a peanut, you get a black hole, also if you shrunk Mount Everest to the size of a nanometer you get a black hole.
Receptors in the ear are stimulated by vibrations of sound waves. Such vibrations are transmitted and amplified through a system of first air-filled and then fluid-filled cavities. In the cochlea, layers of receptors cells with hairlike projections bend in response to the vibrations, firing off signals to the brain. Semicircular canals in the inner ear are responsible for balance: as the head tilts and moves, the flow liquid stimulates hair cells to send impulses to the brain.