No hair but plenty of feathers: are birds black holes?

Abstract

The imitative verb "chirp" is thought to originate from 16th-century Middle English. Meanwhile, this same word has been used to describe the gravitational waves (GWs) emitted from the merger of compact objects, such as black holes and neutron stars, since at least the 1990s. Motivated purely by this linguistic overlap, we study whether the chirps of birds can be modeled by compact binary waveforms. In particular, we consider a test case of the Northern cardinal (Cardinalis cardinalis), finding that its time-reversed chirp can be approximately modeled by that of a high mass ratio, precessing black hole binary, with a number of indications towards extreme matter effects or beyond the Standard Model physics. Importantly, this waveform correspondence is not so straightforward for all bird species, as some chirp morphologies are far more akin to glitches seen in GW observatories. With these comparisons made, we propose an alternative solution to the longstanding philosophical conundrum: rather than the chicken or the egg, perhaps it was the Big Bang which truly came first.

Figures (6)

• Figure 1: The central tenet of this paper: careful investigation of the calls of certain birds may reveal that these creatures actually conceal compact binaries whose radiated gravitational waves match the "chirps" we observe in nature.
• Figure 2: Waveforms obtained from the Northern cardinal time-reversed chirp. The top panel gives the full unmasked bird call. The bottom panel is the isolated portion of the signal corresponding to the dominant spectral track of the chirp, computed via an inverse STFT applied to our masked spectrogram in the lower panel of Fig. \ref{['fig:filtered_spectrogram']}.
• Figure 3: Spectrograms of the Northern cardinal chirp, computed via an STFT on the time-reversed waveform, where the color indicates the magnitude in each frequency bin at a given time. The top panel shows the full spectrogram with the dominant spectral ridge ("main track", dashed white line) determined via our greedy algorithm. The bottom panel shows only the dominant spectral ridge, where we have applied a Gaussian mask which captures the full width of the track.
• Figure 4: Best fit SEOBNRv5PHM (blue dashed) waveform for the dominant spectral ridge of the Northern cardinal chirp (red solid). We restrict the fitting to the modulations beginning at $t\sim -0.25$ s due to noise at early times in the bird chirp inspiral. The best fit corresponds to $q\approx104$, $\chi_{\rm eff} \approx -0.08$, and $\chi_p \approx 0.35$. Our exploratory fitting procedure captures some early-time modulations, but the poor fit near the peak amplitude suggests unmodeled physical processes at work.
• Figure 5: Probability density for the location of the Cardinalis cardinalis chirp on the Earth, based on coordinate data from 916 chirp observations (brown dots). The 90% credible region is denoted by a black dashed contour.