quasi-star

thumb|alt=|upright=1.3|An artist’s impression of a quasi-star, showing a black hole core residing in the massive photospheric envelope of the object

A quasi-star or quasistar (QS), also called a black hole star, is a hypothetical type of extremely massive and luminous star that may have existed early in the history of the universe. Unlike modern stars, which are powered by nuclear fusion in their cores, a quasi-star's energy would come from material falling into a black hole at its core. The formation of such an object would have resulted from the core of a large supermassive protostar collapsing into a stellar-mass black hole, where the outer layers of the protostar are massive enough to absorb the resulting burst of energy without being blown away or falling into the black hole, as occurs with supernovae. They are dubbed as such as they would resemble red giants in structure to an external observer, but scaled-up and powered by an accreting central black hole with luminosities comparable to a Seyfert nucleus.