The recent discovery by LIGO/Virgo of a merging binary having a \sim 2.3 M _ { \odot } black hole and a \sim 2.6 M _ { \odot } compact companion has triggered a debate regarding the nature of the secondary , which falls into the so-called mass gap .
Here we explore some consequences of the assumption that the secondary was a neutron star ( NS ) .
We show with concrete examples of heretofore viable equations of state ( EOSs ) that rapid uniform rotation may neither be necessary for some EOSs nor sufficient for others to explain the presence of a NS .
Absolute upper limits for the maximum mass of a spherical NS derived from GW170817 already suggest that this unknown compact companion might be a slowly or even a nonrotating NS .
However several soft NS EOSs favored by GW170817 with maximum spherical masses \lesssim 2.1 M _ { \odot } can not be invoked to explain this object , even allowing for maximum uniform rotation .
By contrast , sufficiently stiff EOSs that yield 2.6 M _ { \odot } NSs which are slowly rotating or , in some cases , nonrotating , and are compatible with GW170817 and the results of NICER , can account for the black hole companion .