May Negative Mass Objects exist in the sky?

TL;DR

This paper explores the theoretical possibility of negative mass objects existing in space, proposing models within standard and extended gravity theories, and discusses their potential observational signatures and properties.

Contribution

It introduces new models for negative mass objects within standard gravitational equations and scalar-tensor theories, expanding the theoretical landscape of exotic astrophysical objects.

Findings

Negative mass objects can arise as solutions in standard gravity with cosmological constant.

Bound systems of positive and negative mass objects are theoretically possible.

Negative mass objects may produce observable effects akin to anti-gravity.

Abstract

We conjecture the possibility of negative mass objects (NMOs) existing in the sky. It is shown that they may not be so exotic as usually expected. We show that NMOs appear as solutions of standard gravitational equations if we consider the system of a compact positive mass object, cosmological fluid and negative cosmological constant. We also construct models which generate such NMOs as solutions within the two-scalar theory and scalar-Einstein-Gauss-Bonnet gravity inspired by string theory. The orbits of the photon and massive particles are investigated in the background, where there is a negative mass object which realises a kind of effective anti-gravity. It is explicitly found that the bound system consisting of a positive mass object and a negative mass object can be formed in spite that a positive mass object suffers the repulsive force from the NMO. The possibility that such exotic objects might be observed is discussed. A simple conjecture about their possible masses is made, too. As an even more exotic object, we consider a non-trivial object with vanishing mass and investigate its properties.