QSOs are objects that are very far away, but are rather bright, which means that they produce enormous amounts of energy. These objects are believed to be luminous because material is falling into a central black hole and as the material falls in, it heats up and generates radiation. This article explores the relationship between a QSO and its central black hole in more detail.

http://www.raa-journal.org/raa/index.php/raa/article/view/890