Upper bound on the gravitational masses of stable spatially regular charged compact objects

Abstract

In a very interesting paper, Andréasson has recently proved that the gravitational mass of a spherically symmetric compact object of radius R and electric charge Q is bounded from aboveIn the present paper we prove that, in the dimensionless regime Q/M < 9/8, a stronger upper bound can be derived on the masses of physically realistic (stable) self-gravitating horizonless compact objects: M < R 3 + 2Q 2 3R .

Ultra-compact spherically symmetric dark matter charged star objects

“…However, an interesting problem was suggested in [41], i.e., it was posed a question if the addition of some characteristics of horizonless object could improve the upper bound on its gravitational mass. The refinement of the bounds derived in [40] was presented in [41]. On the other hand, geodesic motion determines important features of the spacetime and objects in it.…”

Upper bounds on the compactness at the innermost light ring of anisotropic horizonless spheres

“…And it was also proved that the innermost light ring provides the fastest way to circle a central black hole as measured by observers at the infinity [21][22][23]. Moreover, the existence of stable light rings suggests that the central compact stars may suffer from nonlinear instabilities [24][25][26][27][28][29][30]. And unstable light rings can be used to determine the characteristic resonances of black holes [31][32][33][34][35][36][37][38].…”

The extreme orbital period in scalar hairy kerr black holes

“…It was suggested that the characteristic resonances of black holes can be interpreted as null particles trapped at the unstable circular orbit and slowly leaking out [23][24][25][26][27][28][29][30]. In the regular ultra-compact star spacetime, the existence of stable circular null geodesics could trigger nonlinear instabilities due to that massless fields can pile up on the stable null obit [31][32][33][34][35][36][37][38].…”