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We perform the first fully general relativistic, magnetohydrodynamicsimulations of dynamically stable hypermassive neutron stars with and withoutergoregions to assess the impact of ergoregions on launchingmagnetically--driven outflows. The hypermassive neutron stars are modeled by acompressible and causal equation of state and are initially endowed with adipolar magnetic field extending from the stellar interior into its exterior.We find that, after a few Alfv\'en times, magnetic field lines in the ergostar(star that contains ergoregions) and the normal star have been tightly wound inboth cases into a helical funnel within which matter begins to flow outward.The maximum Lorentz factor in the outflow is $\Gamma_L \sim 2.5$, while theforce-free parameter holds at $B^2/8\pi\rho_0\lesssim 10$. These values areincompatible with highly relativistic, magnetically-driven outflows (jets) andshort $\gamma$-ray bursts. We compare these results with those of a spinningblack hole surrounded by a magnetized, massless accretion disk that launches abona fide jet. Our simulations suggest that the Blandford-Znajek mechanism forlaunching relativistic jets only operates when a black hole is present, thoughthe Poynting luminosity in all cases is comparable. Therefore, one cannotdistinguish a magnetized, accreting black hole from a magnetized hypermassiveneutron star in the so-called mass-gap based solely on the value of theobserved Poynting luminosity. These results complement our previous studies ofsupramassive remnants and suggest that it would be challenging for eithernormal neutron stars or ergostars in a hypermassive state to be the progenitorsof short $\gamma$-ray bursts.

Magnetic Ergostars, Jet Formation and Gamma-Ray Bursts: Ergoregions versus Horizons