# Rapid orbital decay in detached binaries: evidence for circumbinary disks

## TL;DR

This paper investigates whether resonant interactions with circumbinary disks can explain the rapid orbital decay observed in certain detached binary systems, challenging previous assumptions about angular momentum loss mechanisms.

## Contribution

It demonstrates that circumbinary disks with specific masses can account for the observed orbital decay, providing a new explanation for this phenomenon in detached binaries.

## Key findings

- Resonant interactions with circumbinary disks can produce observed orbital-period derivatives.
- The required disk mass range is consistent with inferred disk masses in some systems.
- Magnetic braking is unlikely to explain the decay in fully convective stars.

## Abstract

Some short-period, detached binary systems have recently been reported to experience very rapid orbital decay, much faster than is expected from the angular-momentum loss caused by gravitational radiation alone. As these systems contain fully convective stars, magnetic braking is not believed to be operative, making the large orbital-period derivative puzzling. Here we explore whether a resonant interaction between the binary and a surrounding circumbinary (CB) disk could account for the observed orbital decay. Our calculations indicate that the observed orbital-period derivatives in seven detached binaries can be produced by the resonant interaction between the binary and a CB disk if the latter has a mass in the range of $10^{-4}-10^{-2}~ M_{\odot}$, which is of the same order as the inferred disk mass ($\sim2.4\times 10^{-4}~ M_{\odot}$) in the post-common-envelope binary NN Ser.