NEUTRON STARS (Syllabus: GS Paper 1 - Geography)

Context: Scientists have investigated the inflow of matter onto neutron stars- which are compact stars with masses similar to the Sun, but confined to a very small region like a city. 

Key Points

• Neutron stars can harbor extreme magnetic fields and this work for the first time found a methodology to obtain unique solutions for accretion onto a neutron star. 
• It could help understanding of underlying physical processes around Neutron stars (NS).
• Because of the extreme compactness (mass to radius ratio) of NS, they have large surface gravitational potentials which make them an efficient accretor of surrounding matter. It may be noted, accretion is the process of inflow of matter onto a compact star. 
• The accretion dynamics, however, is strongly dictated by the magnetic fields. 
• The strong magnetic field of the star restricts the infalling matter to flow along these field lines until they reach the poles of the star. 
• It is near the poles where the matter emits most of its kinetic energy in the form of radiation. 
• This enables the flow to slow down, finally settling down onto the NS surface.
• Accretion flow around NS is composed of ionised plasma which is a soup of protons and electrons. 
• Because electrons are almost two thousand times lighter than the protons, they are prone to different radiative emission processes and hence, these species are expected to exhibit different temperature distribution than that of the protons.
• Working in this two-temperature regime is not trivial since they suffer from a very basic problem of degeneracy, which arises because of the presence of more variables than the number of equations of motions available. 
• Degeneracy implies that the equations of motions when solved, produces multiple accretion solutions and hence different observable spectrum even for a given set of constants of motion.