A stellar black hole is a type of black hole formed when a massive star exhausts its nuclear fuel and collapses under its own gravity. These black holes typically have a mass between about three and several tens of times that of the Sun, the Sun being our closest star. The core of the star collapses, while the outer layers may explode in a supernova, leaving behind the black hole. Stellar black holes are detected by observing their effects on nearby objects. For instance, if a black hole is part of a binary system, it can pull material from its companion star, creating an accretion disk. This process emits X-rays, allowing astronomers to identify the presence of a black hole, even though it cannot be seen directly.