Quantum Degeneracy


Protons, electrons and neutrons are members of a set of Composite Particles called fermionsQuantum Degeneracy is a broad term referring to extremely dense systems of fermions

.nbsp; A defined system of fermions has a unique set of quantum numbers associated with every fermion.  Specific types of quantum numbers depend on the target system, like a stellar core, white dwarf star or a neutron star.  The Pauli Excusion Principle is a quantum mechanical rule which prohibits more than one fermion in a system from having exactly the same set of quantum numbers.  For example, a neutral helium atom has two electrons, one with spin=1/2 and the other with the same "spin" cannot be associated with the same helium atom."  Quantum thermodynamics is not a quantum theory; it explains temperature in terms of particle's kinetic energy  Classically, Kinetic energy is defined as 1/2(mass*velocity_squared) and Momentum is defined as mass*velocity.  Thermodynamically, a particle has a temperature of absolute zero when it does not move or vibrate, i.e., its kinetic energy and momentum are zero.  Classically, there are two kinds of energy.  One, kinetic energy is defined as 1/2(mass*velocity_squared), the other, potential energy is defined as mass x acceleration x distance  The definition of quantum energy is a bit involved The Fermi Energy is the difference between the lowest particle energy and highest particle energy in a closed system.  This definition is valid only when there is no kinetic interaction between particles, i.e., at absolute zero temperature.  When a system of particles, like electrons, protons and neutrons, is compressed in space so tightly that every possible quantum state, is occupied by a particle, the lowest particle energy is zero.  Since movement or vibration requires a change in location, the collection has a classical "temperature" of absolute zero.  The Heisenburg Uncertainty Principle (location_uncertainty)*(momentum_uncertainty) GE PlankConstant/2pi.  At gravitational pressures high enough to equal the Fermi energy, only electron Fermi energy, which behaves like classical pressure, effectively resists further gravitational compression. 

Most stars shine by radiating energy produced in their cores from hydrogen fusing into helium.  This process operates, for main sequence stars, such as the Sun, for around 10 billion years.  Massive stars (GT 3 solar masses) fuse hydrogen more rapidly. 

Eventually all stars develop a core of "helium ash" and hydrogen begins to fuse in a shell around the helium core.  Shell fusion presents an increasingly larger radiant outer surface and the overlying matter, which gravitationally compresses the shell, is reduced.  Consequently the shell temperature and pressure drops below that required to sustain fusion.  The overlying matter then gravitationally contracts raising the shell temperature and pressure until fusion reignites.  This results in fusion reactions toggling on and off.  This fusion toggling produces shock waves which push overlying matter outward cooling it and expanding stellar volume.  Externally, the star becomes a variable red-giant. 

As the helium core accumulates, the shell temperature drops below that required for hydrogen fusion (about 14 million degrees).  When hydrogen fusion ceases, the star contracts by self-gravitation raising the temperature high enough in the core for helium to fuse into carbon and oxygen.  A "carbon ash" core accumulates inside the helium fusion zone and a helium fusion shell develops.  large core pulsations which push surface material outward where it cools.  The star becomes larger and more reddish in color.  Eventually, the helium fuel exhausts, fusion ceases, and gravitational contraction again occurs.

At this point, less massive stars, such as the Sun, contract slowly but the core does not get hot enough to fuse carbon or oxygen.  Gravitational contraction raises the internal temperature creating convection zones.  A star like the Sun will contract until matter at the center reaches an electron degeneracy state.  An incompressible electron "crystal" forms containing carbon and oxygen nuclei.  Radiation pressure from the degenerate core will drive about 40% of the star's mass off into space as an expanding shell.  This creates a planetary nebula surrounding a white dwarf star.  Initialially, the white dwarf has an apparent (black body) surface temperature of about 100,000 degrees.  Its surface emits intense ultraviolet radiation which causes gasses in the surrounding planetary nebula to flouresce.  Over bllions of years, the star cools becoming a frozen cinder and the halo dissipates into space.

Stars greater than 3 solar masses continue contracting until the core reaches carbon / oxygen fusion temperature.  A number of fusion reactions occur producing primarily magnesium, neon and silicon.  A complex series of core contractions and toggling of fusion reaction zones between the core and shells eventually results in accumulation of an iron "ash" core.  Stars in this phase pulsate and their energy output varies.  Iron cannot be fused to release energy so an "iron ash" core builds up until its volume is slightly larger than the size of the earth.  Gravitational pressure around the iron core increases until the core collapses into a neutron degeneracy state.  It takes about 10 seconds for the "Earth sized" core to collapse into a ball of neutrons 10 miles in diameter.  The chaos that follows is a type II supernova.  An incredible amount of energy is released, mostly in the form of neutrinos (tiny electrically neutral subatomic particles) as stellar matter outside the core falls inward and collides with the neutron core.  Near the surface of the neutron core, temperatures reach several hundred million degrees and the infalling matter recoils.  The resulting shockwave produces a brilliant cosmic display and contains elements heavier than iron, for example, nickel, gold, silver, uranium, etc.  These heavy elements are created by fusion reactions near the core which require extremely high temperatures and pressure.  Enough gamma radiation is produced to cause damage to carbon-based forms within 200 light-years (1,200,000,000,000,000 miles!).  The ball of neutrons, a neutron star remains and is, in many cases, ejected from the center of the explosion. 

The star's outer layers are blasted into space at thousands of km/sec producing a massive shock wave.  This expanding shell is so bright that it can be seen with the unaided eye in daylight if the event occurs within our Milky Way galaxy.  These explosions can even be observed with small telescopes in galaxies millions of light-years away.  After several months, the blast cloud dims as it expands and cools producing a supernova remnant. The surface of the neutron star slowly decays into proton-electron pairs which are trapped or ejected by the magnetic field.  The neutron star slowly decays via synchrotron radiation emission and particle ejection into polar magnetic jets. 

When core collapse occurs, the neutron star "spins up" like a skater pulling their arms in.  Rotational speeds of 3000 RPM are not uncommon.  The progenitor star's magnetic field is compressed and wrapped up to extremely high flux levels which generates "jets" of protons and high energy radiation aligned with the magnetic field axis.  These jets are detectable at great distances if pointed at an observer.  Because the magnetic and spin axes are seldom coincident, the jets trace circles in the cosmos.  A distant observer located near the beam path will observe a regularly pulsing radiation source, hence, the term pulsar also refers to neutron stars.