Neutron Stars

Neutron Stars

In the last legs of a massive stars death, fusion in the core begins to fuse heavier elements in a Russian nesting doll sense. (Figure 1) With each new element being fused the star gets hotter allowing for fusion of the heavier elements until it the reaches Iron; marking the end of exothermic fusion. Unlike fusing lighter elements, Iron fusion does not release energy. Now with star deprived of an energy source there is no stellar equilibrium (balance of outward and inward pressure) and the core begins to collapse in on itself. When the iron core collapses on itself electrons are slammed into the iron nuclei creating the Neutron star. (Figure 2, Figure 3) The rest of the remaining shells ricochet off the super dense core resulting in a supernova enriching the galaxy with tons of new elements. What were left with is the Neutron star with a mass of about 1.4solar masses but the radius of a small city. To put this into perspective a sugar cubed size chunk of this would weigh around 100 million tons. To make things even more interesting Neutron stars rotate much faster than other stars because they have the ability to retain their momentum from their once larger self. This is due to the conservation of angular momentum; just like a figure skater pulling their arms in to rotate faster, neutron stars pull their mass into a smaller radius.  Along with their rotation neutron stars sometimes pulse with radio and x-ray beams caused by its magnetic poles accelerating particles outwards like a jet. We classify these as pulsars. (Figure 4) Quite possibly the coolest part of a neutron star is what happens when more mass is added to the star. Imagine the neutron star is in a binary system with another star about 1.5times the mass of the sun and as time passes they get closer and closer until the neutron star begins to absorb matter from the other star via its intense gravitational pull. As you know the neutron star is extremely dense, so dense in fact that every possible 3d space-time location for matter is full. So where would all that matter go? As the neutron star begins to absorb the other star its radius counter intuitively becomes smaller and smaller. As stated by the Pauli Exclusion Principle, two fermions (Quantum particle that makes up protons, neutrons etc.) can occupy the same space-time location assuming their momentum or other quantum state is different. (Figure 5, each blue dot is a fermion and the square is its position in physical space and the line represents its momenta) So as the star grows in mass; its physical radius decreases while its 6th dimensional quantum phase space momenta is proportionally increasing. Eventually the neutron star reaches the point of infinite gravitational curvature and the event horizons passes the surface and becomes a black hole. (Figure 6) However that is a topic for another time.