Session
2025 Poster
Location
Brigham Young University Engineering Building, Provo, UT
Start Date
5-5-2025 9:55 AM
Description
Observations reveal that some neutron stars (NS) exhibit high velocities, reaching over 1000 km/s in some instances. This cannot be attributed to the orbital velocity of the NS around our Milky Way galaxy, as it is around 250 km/s on average. The origin of this phenomenon, known as a pulsar kick, is not fully understood and remains a subject of debate among astrophysicists.
During NS formation, the rotation and strong (potentially asymmetric) magnetic field of its progenitor star may result in an asymmetric collapse of the star's core plasma. If this is the case, we might anticipate the formation of dense neutron matter slightly offset from the center of the forming NS, which will be the source of subsequent neutrino radiation. This offset results in an imbalance of neutrinos reaching opposite sides of the NS, creating a net momentum of neutrino radiation into space and propelling the NS in the opposite direction.
Due to strong interactions of high energy (~10-100 MeV) neutrinos with dense neutron matter, we expect the neutrinos to propagate throughout the NS in a diffusive manner. Hence, we used a diffusion model to investigate neutrino emissions from an offset source and analytically proved that it will result in significant anisotropic emissions. From this, we derived a novel linear relationship between the velocity of a pulsar kick and the offset percentage (relative to NS radius), with the proportionality constant dependent solely on the average energy of the formed neutrinos. This formula predicts kickback velocities consistent with observational data from small asymmetries (2-7% offset for 100 MeV neutrinos). Our findings suggest that an offset neutrino source can indeed account for significant recoil velocities and thus, it seems a full theory explaining pulsar kicks should most certainly include anisotropic neutrino emission as a primary cause.
High-Velocity Pulsar Kicks via Anisotropic Neutrino Emission
Brigham Young University Engineering Building, Provo, UT
Observations reveal that some neutron stars (NS) exhibit high velocities, reaching over 1000 km/s in some instances. This cannot be attributed to the orbital velocity of the NS around our Milky Way galaxy, as it is around 250 km/s on average. The origin of this phenomenon, known as a pulsar kick, is not fully understood and remains a subject of debate among astrophysicists.
During NS formation, the rotation and strong (potentially asymmetric) magnetic field of its progenitor star may result in an asymmetric collapse of the star's core plasma. If this is the case, we might anticipate the formation of dense neutron matter slightly offset from the center of the forming NS, which will be the source of subsequent neutrino radiation. This offset results in an imbalance of neutrinos reaching opposite sides of the NS, creating a net momentum of neutrino radiation into space and propelling the NS in the opposite direction.
Due to strong interactions of high energy (~10-100 MeV) neutrinos with dense neutron matter, we expect the neutrinos to propagate throughout the NS in a diffusive manner. Hence, we used a diffusion model to investigate neutrino emissions from an offset source and analytically proved that it will result in significant anisotropic emissions. From this, we derived a novel linear relationship between the velocity of a pulsar kick and the offset percentage (relative to NS radius), with the proportionality constant dependent solely on the average energy of the formed neutrinos. This formula predicts kickback velocities consistent with observational data from small asymmetries (2-7% offset for 100 MeV neutrinos). Our findings suggest that an offset neutrino source can indeed account for significant recoil velocities and thus, it seems a full theory explaining pulsar kicks should most certainly include anisotropic neutrino emission as a primary cause.