Gravitational waves and cosmic boundary

TL;DR

This paper explores whether space-based gravitational wave detectors can identify a hypothetical reflective cosmic boundary at high redshift, emphasizing the importance of black hole mergers and detector networks in this quest.

Contribution

It demonstrates that gravitational waves are the only feasible method to detect such a cosmic boundary and highlights the role of black hole mergers and detector networks in this detection.

Findings

Gravitational waves are the only means to detect the cosmic boundary signatures.

Black holes with masses between 10^3 and 10^6 solar masses are suitable for detection.

Detecting multiple coincident gravitational wave events increases the likelihood of identifying the boundary.

Abstract

Space-based gravitational wave detectors have the capability to detect signals from very high redshifts. It is interesting to know if such capability can be used to study the global structure of the cosmic space. In this paper, we focus on one particular question: if there exists a reflective cosmic boundary at the high redshift ($z>15$), is it possible to find it? We find that, with the current level of technology: 1) gravitational waves appear to be the only means with which that signatures from the cosmic boundary can possibly be detected; 2) a large variety of black holes, with masses roughly in the range $(10^3\sim 10^6) {\rm~M_\odot}$, can be used for the task; 3) in the presumably rare but physically possible case that two merger events from the growth history of a massive black hole are detected coincidentally, a detector network like TianQin+LISA is essential in help improving the chance to determine the orientation of the cosmic boundary; 4) the possibility to prove or disprove the presence of the cosmic boundary largely depends on how likely one can detect multiple pairs of coincident gravitational wave events.