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Messier 57

Distance: 1,630 light years

by Robert Gendler

One of the best examples of a planetary nebula is the Ring Nebula which represents the gaseous remains of a sunlike star which has entered its final stages of evolution.

The intense radiation from the stellar remnant ionizes the stars previously ejected gases. The inner shell glows green from ionized oxygen (OII and OIII) and nitrogen while hydrogen in the outer shell glows red. The stellar object in the center is a 15th magnitude planet sized “white dwarf”. Now over 100,000 degrees the stellar remnant or white dwarf produces heat not by nuclear fusion but by its incredible density of a metric ton/cubic cm.

The planetary nebula stage of an intermediate mass star lasts only 10 to 30 thousand years, an astronomical instant in the overall life of a star. Eventually the ejected envelope disperses into the interstellar medium enriching it with both light and heavier elements originally created deep within the nuclear furnace of the now dead star.

The outer shell of M57 expands at a rate of about 1 arc seconds per century. Astronomers have used its expansion rate to calculate the age of M57 which is estimated at 6000 to 8000 years old. Although the brightest part of M57 extends 1.4 arc minutes, deep observations of the nebula mostly in h-alpha light reveal an outer halo extending 3.5 arc minutes.

9 months ago  /  317 notes  /  Source: ikenbot