Geodesic noise and gravitational wave observations by pulsar timing arrays

Signals from millisecond pulsars travel to us on geodesics along the line-of-sight that are affected by space--time metric. The exact path-geometry and redshifting determine observed Time-of-Arrival (ToA) of pulses. metric is determined distribution dark matter, gas, stars in galaxy and, final stages travel, solar system bodies. inhomogeneous stellar masses can have a small but significant statistical effect ToAs through perturbation geodesics. This will result additional noise ToA observations may affect Pulsar Timing Array (PTA) constraints gravitational waves at very low frequencies. We employ simple model for our estimate scale both static dynamic sources what we term generically "geodesic noise". find geodesic has standard deviation ${\cal O}(10)$ ns typical lines-of-sight. suggests relevant estimates PTA sensitivity limit future efforts detection PTAs.