In most cases, a black hole is found by looking for X-rays coming from a hot disk of material swirling around it. (sciencedaily.com)
The spinning disk of material around a star is barely stable, held in equilibrium by gravity and the outward pressure of its own warmth. (scientificamerican.com)
«For instance, our own moon is low in volatile elements because it slowly coalesced from a churning, hot disk of material surrounding the Earth.» (sciencemag.org)