Multipole decomposition of redshift drift -- model independent mapping of the expansion history of the Universe

International audienceWe consider redshift drift in a general space-time as expressed in terms of physically interpretable multipole series. An important realization from the derived results is that redshift drift cannot in general be thought of as a direct probe of the average expansion rate of the Universe due to the presence of structure along the light beams from the astrophysical sources to the observer. We also predict the general presence of a dipolar and a quadrupolar offset in the detection of redshift drift for observers placed in locally anisotropic environments