LIGO detected Gravitational Waves from a collision event that happened 8 million light years away between a Black Hole and a mystery object that resides in the "mass gap". The initial speculation is that the object is either another black hole or a neutron star, but the article mentions that it would be the least massive black hole ever discovered or the most massive neutron star. The object is just beyond the solar mass of the largest neutron star discovered but one of the scientists interviewed suggested that it would still make them have to reconsider how matter behaves at extremely high densities if it were a neutron star. So it seems like they are leaning towards Black Hole or perhaps there was a neutron star merger that happened prior to this event.