The phrase "stellar debris" refers to the leftover material from stars that have exploded or died. It includes things like gas, dust, and other remnants scattered in space after the star's demise. Full definition
From simulations run by others, the researchers conclude that the optical and UV bursts likely originated from the collision of stellar debris on the outer perimeter of the black hole. (sciencedaily.com)
«Scientists identify a black hole choking on stardust: Data suggest black holes swallow stellar debris in bursts.» (sciencedaily.com)
The resulting stellar debris, swirling ever closer to the black hole, collided with itself, giving off bursts of optical and UV light at the collision sites. (sciencedaily.com)