Galactic hum
  A number of earth's tremor spectral peaks show a persistent narrow bandwidth
incompatible with any geophysical or instrumental origin. These peaks, located
at frequencies lower than a few mHz, are in principle consistent with the earth
strain waves induced by monochromatic gravitational waves. Exploring this
hypothesis under the current cosmological constraints yields that the tremor
peaks below 2 mHz are in apparently significant coincidence with the
theoretical emission of two binary systems each consisting of a small main
sequence star with mass $\sim 10^{-1} M_{\odot}$, captured by Sgr A* in a close
orbit.
