Why is the luminosity of a galaxy sometimes high despite having no visible stars?

The luminosity of a galaxy being high despite the absence of visible stars can indeed indicate the existence of a supermassive black hole at its center. Supermassive black holes can emit significant amounts of energy, particularly in the form of X-rays and other radiation, due to the interaction of infalling matter in an accretion disk surrounding the black hole. This energy output can contribute to the overall luminosity of the galaxy, even when the stars are not directly observable.

In contrast, the other options suggest different scenarios that do not directly explain the observed luminosity in the absence of visible stars. Continuous star formation, while potentially leading to high luminosity, usually would result in the presence of stars being observable. Cosmic dust can indeed obscure stars, but it doesn’t inherently account for the luminosity itself when no stars are visible. Finally, while a young and developing galaxy may exhibit high energy generation, it is not a definitive explanation for high luminosity without visible stars, as older galaxies can also possess high-energy phenomena unrelated to stellar visibility.