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8/15/2015

Is Messier 57 Really, I mean REALLY The Ring Nebula?



     Early on a Saturday morning and I was going through some older Hubblecasts on YouTube when I saw this one on the Ring Nebula. Messier 57 is a favorite target this time of the year for many amateurs and I found Dr. J's insight into its true shape really interesting. More like Messier 76, The Little Dumbbell, if the perspective was changed. Enjoy this!



     Dr. J provides a wonderful view of how we get white dwarf stars in a general basis. There are in general two white dwarf star types found. The first is for those stars that are 4 solar masses or less, down to the mass of the Sun, perhaps .5 the mass of the Sun. These stars end their lives as carbon-oxygen white dwarf stars as they use the triple alpha process to fuse helium into carbon and oxygen at the core.  They stop there as they do not have the capacity to burn oxygen into neon. As they approach the end of their lives, these stars (a vast majority in the universe) will on the Hertzsprung-Russell diagram be on the asymptotic-giant-branch as reflected in this diagram under the green AGB branch which takes off from the 2 solar mass star.


from: "Stellar evolutionary tracks-en" by derivative work: Rursus (talk)Stellar_evolutionary_tracks-en.PNG: *derivative work: G.A.SStellar_evolutionary_tracks.gif: Jesusmaiz - Stellar_evolutionary_tracks-en.PNG. Licensed under CC BY 3.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Stellar_evolutionary_tracks-en.svg#/media/File:Stellar_evolutionary_tracks-en.svg

     These stars per above, that fuse helium into carbon and oxygen will end up as red giants and at the end of the ASB cycle will be comprised of a outward hydrogen burning shell, followed by a helium burning shell and a carbon and oxygen core. These stars (like our Sun) will then through stellar winds throw off their hydrogen and helium shells and form a planetary nebula while retaining only that earth size carbon oxygen core. The more massive the white dwarf, the smaller its size will be.

   For stars that come in between 4 solar masses to somewhere around 8 solar masses, they are capable of burning hydrogen into helium and then ignited helium into carbon burning producing oxygen-neon-magnesium in the core. However, these stars never become hot enough to ignite neon burning so the result is their core becomes a oxygen-neon-magnesium core, and thus they leave a oxygen-neon-sodium-magnesium white dwarf.  Their outer shell is thrown off via stellar winds, sending the hydrogen, helium and carbon shells out leaving just the oxygen-neon-magnesium white dwarf. Then for somewhere between 10,000 to 50,000 years, the planetary nebula is lit up by the  ultra violent radiation coming from the white dwarf. As the white dwarf cools, the planetary nebula becomes fainter as the radiation doesn't light it up until the planetary nebula fades into the interstellar medium.

     If a star is around 8 solar masses or greater (initially, it can most likely become under 8 solar masses slightly as it goes through its evolutionary stages) it may ignite neon fusing and then continue fusing heavier elements until it reaches iron, at which point the star will end up in a supernova explosion.

     The takeaway from this video for me is that how we view a planetary nebula is really relative to how we view it from our perspective and line of sight from earth! That helps us to determine its shape. I have to wonder if any study has picked up not only on the elements and nature of the elements in a planetary nebula to cause its shape, but if taking a basic planetary shape and changing it via a computer model to reflect how different planetary nebula may look if our line of sight and thus our perspective were to change. Cool thought! Keep enjoying the wonders of the night sky!