Three Beautiful Ghosts

24 Dec 2016

Observing planetary nebulae is, in a word, awe-inspiring.

It’s awe-inspiring because one is looking at a star dying in the night sky, its shroud of cast-off gas forming one of the most beautiful objects in the cosmos.

It’s awe-inspiring because with some planetary nebulae, one can see the dying star’s exposed core – an incredibly hot, tiny white dwarf – lying at the centre of the bubble of glowing gas, and illuminating the ghost of its former self in spectacular colours and shapes.

It’s awe-inspiring because although the planetary nebula signals the end of a star, it also signals a new beginning. Its cargo of stellar material plays a crucial role in the chemical enrichment and evolution of the universe as the elements created in the star are returned to the interstellar medium. Out of this material new stars, planets, shrubs and the likes of us are formed.

*The first planetary nebula was observed by Charles Messier on July 12, 1764 and listed as M27 in his catalogue of nebulous objects. Image credit Hubble/ESO*

It’s awe-inspiring because a planetary nebula is so ephemeral – the whole show is over in a few tens of thousands of years. The glowing gas dissipates into space leaving the white dwarf behind, which itself will eventually cool to become a dead black dwarf – a charred cosmic cinder alone in the night. A flash of wondrous beauty in the universe… and we get to see it.

It’s awe-inspiring because one is looking at the fate of our own Sun in billions of years time. One day our life-giving star will be a smouldering ember embedded in a cosmic work of art, our own atoms fading into the blackness of space.

It’s awe-inspiring because like snowflakes, no two planetary nebulae are exactly the same. This is for a number reasons – the stars that create them can have different masses, sizes, temperatures, and chemical compositions. Furthermore, we see different planetary nebulae at different moments in their evolution – some we see just as they are beginning to form, some are later stage and we see them fully formed.

cactus-flower — *A planetary nebula in a clay pot*

As a complete aside, the beauty and ephemeral nature of planetary nebulae remind me of my Echinopsis Oxygona, a rough and spiky cactus whose flower of astonishing beauty and delicacy opens for one night and wilts and dies in the morning sun; an exquisite ghostly flower in starlight.

Observations

16″ f/4.5 Dobs; magnifications of 130x, 228x and 333x

Last night I called on three beautiful southern belles of the planetary nebulae world.

It was perfect observing conditions and allowed me to linger on each one to my heart’s content, marveling at the beauty and intricate detail I was seeing in the eyepiece, and the Hubble-captured beauty and intricacy I was seeing in my mind’s eye… all the while pondering stellar life and death, time before, time after, one’s own atoms and the use to which we put them during this brief flash of life.

NGC 3132 – The Eight-Burst Nebula

RA 10 07 01.8 Dec -40 26 09 Mag 8.2 Size 88″

In the Hubble image, the bright star near the centre is a foreground star. The tiny one right beside it is the dying star that created this beautiful planetary nebula.

What a fantastic planetary nebula it is in the telescope. At low magnification it is a small, glowing halo of brightish light with a bright centre. The foreground mag 10 star is cunningly situated where one would expect to see the white dwarf… which I unfortunately, couldn’t see.

Higher magnification and the OIII filter reveal a hint of the planetary nebula’s structure – it becomes a ring of faint knottiness – grey silky beads on a background of grey silk – more prominent in the southern half, with a diffuse appearance in the northern half. The inner section was a smooth even glow of nebulosity. Others report seeing a bluish/greenish colour to the planetary nebula, but to my eye it was shades of beautiful grey against the velvet-black sky.

NGC 5189 – The Spiral Nebula

RA 13 33 30.8 Dec -65 58 29 Mag 10.3 Size 140″

What a beauty! At low magnification it appears as an elongated glow of pale grey nebulosity with a brighter core. Higher magnification and the OII filter reveal its large size and irregular structure: it has the most gorgeous bright S-shaped twist embedded in a grey shell of nebulosity. It actually resembles a small barred spiral galaxy. The twisted bar is irregular with beads of knotty nebulosity. Here and there a few tiny foreground stars are superimposed on the nebula. I couldn’t make out the faint mag 14 central star which lies just south of the bar.

NGC 3918 – The Blue Planetary

RA 11 50 18.1 Dec -57 10 58 Mag 8.4 Size 23″

John Herschel discovered this planetary nebula and observed it a number of times, each time remarking on its beautiful rich blue colour. And it certainly is a beautiful rich blue colour; I’d say the bluest object I’ve seen up there. It is a beautiful little planetary nebula in all ways – its incredible colour, its very high surface brightness and the way it appears – as Herschel described it, “A perfect planetary disc 6 arcsec diameter; quite sharp, with not the least haziness.” Situated in a rich star field, it appears as if it is floating in the middle of a oval ring of mag 11 and 12 stars. No sign of its central star.