Formation of Mass Gap Objects in Highly Asymmetric Mergers

The LIGO/Virgo Collaboration (LVC) recently reported the detection of GW190814, a merger of a ${23}_{-0.9}^{+1.0}\,\,{M}_{\odot }$ primary black hole (BH), and a ${2.6}_{-0.08}^{+0.08}\,\,{M}_{\odot }$ secondary. The secondary's mass falls into the mass gap regime, which refers to the scarcity of compact objects in the mass range of 2–5 $\,{M}_{\odot }$. The first clue to the formation of GW190814 lies in the fact that the primary is a very massive BH. We suggest that the secondary was born as a neutron star (NS) where a significant amount of the supernova ejecta mass from its formation remained bound to the binary due to the presence of the massive BH companion. The bound mass forms a circumbinary accretion disk, and its accretion onto the NS created a mass gap object. In this scenario, LIGO/Virgo will only detect mass gap objects in binary mergers with an extreme mass ratio. We also predict a correlation between the mass of the secondary and the mass of the primary in such asymmetric mergers. Our model can be tested with future data from the LVC's third observing run.