Wading through the wealth of data from ESA’s Gaia mission, scientists have uncovered a ‘sleeping giant’. A large black hole, with a mass of nearly 33 times the mass of the Sun, was hiding in the constellation Aquila, less than 2000 light-years from Earth. This is the first time a black hole of stellar origin this big has been spotted within the Milky Way. So far, black holes of this type have only been observed in very distant galaxies. The discovery challenges our understanding of how massive stars develop and evolve.
Matter in a black hole is so densely packed that nothing can escape its immense gravitational pull, not even light. The great majority of stellar-mass black holes that we know of are gobbling up matter from a nearby star companion. The captured material falls onto the collapsed object at high speed, becoming extremely hot and releasing X-rays. These systems belong to a family of celestial objects named X-ray binaries.
When a black hole does not have a companion close enough to steal matter from, it does not generate any light and is extremely difficult to spot. These black holes are called ‘dormant’.
https://www.esa.int/Science_Exploration/Space_Science/Gaia/Sleeping_giant_surprises_Gaia_scientists