THE SOUTHWORTH PLANETARIUM

207-780-4249   www.usm.maine.edu/planet

70 Falmouth Street   Portland, Maine 04103

43.6667° N                   70.2667° W 

Altitude:  10 feet below sea level

Founded January 1970

Julian date: 2458784.16

2019-2020:  XL

               "Find a way or make one."

               -Robert Peary, co-discoverer of the North Pole and Portland native

                 

THE DAILY ASTRONOMER

Monday, October 28, 2019

The Blue Snowball Nebula

NGC 7662: The Blue Snowball Nebula.  

The night sky is fiercely alive with the most vibrant colors!    Our human view of the night sky, well, isn't.   As our eyes are not developed to perceive colors at low light levels, the firmament often seems devoid of colors, save for the rosy fingered dawns and elemental dusk fires.       

Today's excursion into the Universe brings us to the Blue Snowball Nebula, a beguilingly beautiful planetary nebula of indeterminate distance within the constellation Andromeda the Chained Princess. An expanding shell of gases envelope a white dwarf stellar remnant with a surface temperature exceeding 75,000 degrees.     At apparent magnitude 8.6, the Blue Snowball Nebula is more than six times fainter than the dimmest naked eye star.  However, observers with a small recreational telescope can observe it as a star smeared by a whisper of nebulosity.     Through moderate sized telescopes (6" aperture), one can observe a blush tint.  Through larger scopes, one can detect a hint of the color variation that is so pronounced in the above image.

Not only does the Blue Snowball Nebula provide another example of the myriad masterpieces adorning the depths of the heavens.  It also foreshadows the Sun's ultimate fate: in the remote future when it exhausts its core fuel reserves and concludes its life cycle.    Presently, the Sun generates copious energy through core thermonuclear fusion reactions: specifically, the Sun is fusing hydrogen into helium and in the process transmuting a minute amount of the hydrogen into energy.    The energy pressure exerted outward precisely counterbalances the unrelenting gravitational contraction to lend the star its stability: a state called "hydrostatic equilibrium."  Although the Sun will deplete its core hydrogen reserves in about five billion years, its core temperature will ultimately increase so as to fuse the helium into carbon.   Prior to the initiation of these helium fusion reactions, its outer layers will expand dramatically, causing the Sun to become  a red giant.   The Sun will contract to a smaller volume when the helium reactions commence.   Once the Sun exhausts its core helium, it will not be able to fuse carbon as it lacks the matter necessary to induce pressures and temperatures required for this more advanced fusion reaction.      

The Sun will expel its outer layers into space, leaving behind an ultra hot planet-sized remnant called a white dwarf.     The outer layer will form a planetary nebula.    This nebula is not so named because of the size of its dwarf, but because a rather obscure French astronomer ,Antoine Darquier de Pellepoix, observed the Ring Nebula in 1779 and described it as being similar to Jupiter in size and appearance.  William Herschel also noted the nebula's planet-like appearance, henee the continued use of the term "planetary nebula" indicating the gaseous remains of a solar-mass star.

Antoine Darquier de Pellepoix

(1718-1802)

The French astronomer who coined the

term "planetary nebula"

The white dwarf star in the nebula's center will slowly cool through the highly inefficient radiative cooling process. (Convection cools hot material much more quickly.)   After billions of years, the dwarf will fade to black as it finally releases its trapped heat energy into space.   The white dwarf will persist for so long despite the absence of fusion reactions due to "electron degeneracy."  Electrons within the dwarf will repel each other with sufficient force to counteract the gravitational contraction pushing inward.

The constellation Andromeda ascends through the eastern evening sky tonight.  Well concealed within the constrained princess lurks a gorgeous azure blue nebula formed by the material expulsion of a distant star.  Eventually, the heated gases will cool and dissipate, leaving an isolated stellar remnant.      By seeing the Blue Snowball Nebula we're seeing a preview of our own star's demise.  It makes one wonder how many beings will observe that nebula about 6.5 billion years from now and how enchantingly beautiful the Sun's death throes will become. 

TO SUBSCRIBE TO OR UNSUBSCRIBE FROM THE "DAILY ASTRONOMER" LIST-SERVE:    http://lists.maine.edu/cgi/wa?SUBED1=DAILY-ASTRONOMER&A=1