Formation of mass gap objects in highly asymmetric mergers

Abstract

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 the 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.

arXiv commentAccepted for publication in ApJ Letters

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