Reshid, Remudin (PhD)Gidey, Tesfay2019-08-232023-11-042019-08-232023-11-0411/3/2017http://etd.aau.edu.et/handle/123456789/18814In this thesis, magnetic _eld decay due to gravitational radiation in neutron star (NS) is theoretically studied. By considering the inuence of the \dynamo mechanism"on the generation of a strong magnetic _eld in NS. A NS formed as a large star die in a type II supernova, and their magnetic _elds during formation is 1012 Gauss and 1015 Gauss for both magnetars and pulars, respectively. But their magnetic _eld is decreased. Thus, this study focuses on by how much does the magnetic _eld decay using the mathematical calculation of decay law equation. Based on our _ndings, we have two results. The _rst result shows that, the magnetic _eld of a rotating NS depends only on the decaying time since the moment of inertia is constant. The second result also shows, the magnetic _eld of a rotating NS depends on the decaying time and rotational frequency since moment of inertia varies as a function of rotational frequency. The variation in moment of inertia causes to the variation in braking index as a function of rotational frequency. Thus, the quadrapole magnetic _eld is decaying for positive _ and increased for negative _ , respectively.enMagnetic FieldGravitational RadiationNeutron StarThesis