Impact of large-mass constraints on the properties of neutron stars

Abstract

The maximum mass of a nonrotating neutron star, 𝑀 TOV , plays a very important role in deciphering the structure and composition of neutron stars and in revealing the equation of state (EOS) of nuclear matter. Although with a large-error bar, the recent mass estimate for the black-widow binary pulsar PSR J0952-0607, i.e., 𝑀 = 2.35 ± 0.17 𝑀 , provides the strongest lower bound on 𝑀 TOV and suggests that neutron stars with very large masses can in principle be observed. Adopting an agnostic modelling of the EOS, we study the impact that large masses have on the neutron-star properties. In particular, we show that assuming 𝑀 TOV 2.35 𝑀 constrains tightly the behaviour of the pressure as a function of the energy density and moves the lower bounds for the stellar radii to values that are significantly larger than those constrained by the NICER measurements, rendering the latter ineffective in constraining the EOS. We also provide updated analytic expressions for the lower bound on the binary tidal deformability in terms of the chirp mass and show how larger bounds on 𝑀 TOV lead to tighter constraints for this quantity. In addition, we point out a novel quasi-universal relation for the pressure profile inside neutron stars that is only weakly dependent from the EOS and the maximum-mass constraint. Finally, we study how the sound speed and the conformal anomaly are distributed inside neutron stars and show how these quantities depend on the imposed maximum-mass constraints.

On the Sound Speed in Neutron Stars

“…This new mass bound has no impact on the main results and conclusions presented here. While a detailed discussion is beyond the scope of this paper, the impact of very large maximum masses on the internal properties of neutron stars has instead been analyzed (Ecker & Rezzolla 2022).…”

Masses of Compact (Neutron) Stars with Distinguished Cores

“…One has to add GW190814: gravitational waves from the coalescence of a 23 solar mass black hole with a 2.6M compact object [82]. An intriguing question concerns a possible mass gap between compact-star maximum-mass [83] and light black holes, cf., [84,85].…”

Static neutron stars perspective of quadratic and induced inflationary attractor scalar-tensor theories

“…After that event, neutron stars (for reviews and textbooks see [3][4][5][6][7]) and other astrophysical compact objects enjoy an elevated scientific role. Specifically, neutron stars are at the crossroads of many scientific eras, like nuclear theory [8][9][10][11][12][13][14][15][16][17][18], high energy physics [19][20][21][22][23], modified gravity [24][25][26][27][28][29][30][31][32][33] and astrophysics [34][35][36][37][38][39][40][41][42][43][44][45][46]. The role of modified gravity in neutron star physics is still questioned and under investigation.…”