Chaera

The Chaera are a sentient alien species that photosynthesize X-ray radiation. They are confined to the accretion disk of a small black hole which they worship as a deity, but they probably did not evolve there.

Anatomy & Physiology
A Chaera is a stingray-like creature approximately a meter across. It has no discernible head or mouthparts, and its four eyes are placed equidistant around the edge of its body.

Diet
Chaera perform photosynthesis using the X-ray radiation emitted by "God," the black hole where they live. They absorb this radiation by exposing their undersides to the glow of the black hole.

Homeworld
The Chaera inhabit the accretion disk of "God", a mini black hole roughly the mass of Jupiter. "God" orbits a G-class star, located 54 light-years from Sol, at a distance of 5 AU. It is implied that "God" is artificial and that aliens created it out of a gas giant for unknown reasons. The Chaera themselves live on the surfaces of larger worldlets in the accretion disk, moving around and between them as needed to feed and socialize.

The Chaera did not evolve in the accretion disk, though. Instead, it is more likely that they evolved on the system's sole terrestrial world. Millions of years ago, unknown aliens arrived in the system and mined it for resources, creating "God" and contaminating the planet's atmosphere with hydrogen. The hydrogen caused a greenhouse effect that left the planet uninhabitable, forcing the Chaera or their ancestors to flee to "God." The Chaera probably modified themselves to some extent to survive in their new environment.