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| Cropped image from a stack captured with the Jodrell Plank Observatory's 127mm Meade Apo refractor and a 600d Canon DSLR. Credit:Kurt Thrust. |
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| Annotated image credit: Astrometry.net |
" Planetary nebulae have nothing to do with planets! Indeed they should remind us that everything in the Universe, you, me, the Observatory cat Comet and stars have finite lives. Stars, even the biggest, hottest and most short lived have lives measured in millions if not billions of years but eventually everything comes to an end.
To explain what is happening in the above image. Approximately 10,000 years ago, a medium sized star not unlike our Sun, ran out of fuel, expanded and started pulsating losing gas as it went. Over time this gas, affected by the stars magnetic field, expanded in two cone like lobes in opposing directions The nebula we see from Earth is side on with one lobe to the left and one to the right in our image. The gas shown in red is ionized hydrogen, that shown in blue is doubly ionized oxygen.
Stars are enormous balls of gas, which over time collapse under the effect of gravity until the very central core becomes so compressed and hot such that nuclear fusion of hydrogen commences. The nuclear furnace at a stars core creates an outward pressure which balances the inward pressure of gravity and all is well and 'hunky-dory'!
The larger the star the hotter it is and at higher temperatures the faster nuclear fusion consumes the hydrogen fuel. Large hot stars have shorter lives than smaller cooler stars because they use their larger reserves of fuel much much faster than their smaller cousins.
A star's end game, when fusion can no longer provide sufficient outward pressure to resist gravity, is is only dependant upon mass at the point of collapse.
Stars happily fusing hydrogen to create helium, and maintaining equilibrium with gravity, are said to be on the 'main-sequence'
Very cool and tiny stars, having masses less than 0.08 that of the Sun, known as brown dwarfs, never become main-sequence stars.
Stars with a mass less than 1.4 times the mass of our Sun will, after leaving the main-sequence, first expand to form cool red giants. Over time these stars will pulsate ejecting outer layers of gas. The envelope of gas becomes separated from the core. This thin shell expands and cools creating a planetary nebula. The very hot core sits at the centre of the planetary nebula shining for millions of years solely by the radiation of heat. The material in a white dwarf no longer undergoes fusion reactions, so the star has no source of energy. Consequently, it cannot support itself by the heat generated from fusion against gravitational collapse, but is supported only by electron degeneracy pressure, causing it to be extremely dense. In the far distant future, our Sun will expand to create a planetary nebula and a white dwarf star.
Stars with a mass between 1.4 and 3 times the mass of our Sun continue to contract under the force of gravity which overcomes the outward pressure created by electron degeneracy. The material continues to compress until the protons and electrons are squeezed into neutrons. Above a certain density and pressure, the neutrons are subject to quantum laws and become a degenerate gas. The gas has sufficient pressure to withstand the gravitational force and equilibrium is achieved. A Neutron star is thus formed.
When stars with a mass in excess of 3 solar masses run out of fuel to fuse, there is an enormous explosion, which is called a 'supernova'. Depending upon how much mass is lost in the process the core collapses to form a 'neutron star' or a 'black hole'.
Most stuff in space spins and stars are no exception. Anything that collapses inwards and has a rotational spin, speeds up as it collapses. Neutron stars that spin are called 'pulsars'. It is thought that as many as 10% of white dwarf stars have strong magnetic fields associated with spin and density".- Karl Segin outreach coordinator at the Jodrell Plank Observatory.
