Probable detections that are not confidently identified as gravitational wave events are designated LVT ("LIGO-Virgo trigger"). Known gravitational wave events come from the merger of two black holes (BH), two neutron stars (NS), or a black hole and a neutron star (BHNS). Some objects are in the mass gap between the largest predicted neutron star masses (Tolman–Oppenheimer–Volkoff limit) and the smallest known black holes.