# Chirping compact stars: gravitational radiation and detection degeneracy with binary systems A conceptual pathfinder for space-based gravitational-wave observatories

## TL;DR

This paper demonstrates that gravitational waves from certain compact star systems are indistinguishable from those emitted by other binary systems within specific frequency ranges, creating a detection degeneracy challenge for space-based observatories.

## Contribution

It introduces the concept of chirping ellipsoids and shows their GW signals are degenerate with other binary systems, highlighting a new detection challenge for space-based gravitational-wave detectors.

## Key findings

- GW signals of CELs are indistinguishable from DWDs and EMRIs in certain frequency ranges.
- Detection rates of CELs, DWDs, and EMRIs are similar in the local universe.
- Detection degeneracy poses a challenge for identifying the true source of observed GWs.

## Abstract

Compressible, Riemann S-type ellipsoids can emit gravitational waves (GWs) with a chirp-like behavior (hereafter chirping ellipsoids, CELs). We show that the GW frequency-amplitude evolution of CELs (mass $\sim 1$~M$_\odot$, radius $\sim10^3$~km, polytropic equation of state with index $n\approx 3$) is indistinguishable from that emitted by double white dwarfs (DWDs) and by extreme mass-ratio inspirals (EMRIs) composed of an intermediate-mass (e.g.~$10^3~M_\odot$) black hole and a planet-like (e.g.~$10^{-4}~M_\odot$) companion, in a specific frequency interval within the detector sensitivity band in which the GWs of all these systems are quasi-monochromatic. We estimate that for reasonable astrophysical assumptions, the rates in the local Universe of CELs, DWDs and EMRIs in the mass range considered here, are very similar, posing a detection-degeneracy challenge for space-based GW detectors. The astrophysical implications of this CEL-binary detection degeneracy by space-based GW-detection facilities, are outlined.