They can be «observed,» however, by the effects of their enormous gravitational fields on nearby matter. (britannica.com)
Astronomers previously thought that this type of «ultraluminous X-ray source» was likely to be made up of black holes five to 50 times more massive than our sun, radiating energy as they pull in nearby matter. (sciencedaily.com)
As detailed in this video, Laniakea's discovery emerged from measurements of galactic positions and velocities that reveal how galaxies are moving in relation to concentrations of nearby matter and the universe's overall expansion. (scientificamerican.com)