Sand and Stars

The Exquisite Little Homunculus 

Image credit Hubble/ESO

3 Jan 2017

Created by the near-death experience of one of the most massive and violently unstable stars known to astronomers, the Homunculus Nebula is one of the strangest, most intriguing and visually stunning objects in the sky to observe.

At the turn of the 19th century, the binary star system Eta Carinae was a faint and undistinguished star in the night sky. Then, on the evening of December 16, 1837, John Herschel, who was in Cape Town in order to catalogue the stars, nebulae, and other objects of the southern skies, recorded that it had brightened to outshine Rigel (one can hardly imagine his astonishment). This event marked the beginning of a roughly 18-year period known as the Great Eruption. By April 1843, it was the second brightest star in the sky, outshone only by Sirius (which is almost a thousand times closer to Earth). Eta Carinae then slowly dimmed and, by 1868, it was no longer visible to the naked eye. It started to brighten again in the 1990s and it is once again visible to the naked eye – a faint orange star shining from within the cocoon of its own making.

During the Great Eruption, Eta Carinae, which is more than 100 times the mass of the Sun, ejected a vast envelope of stellar material – and the glowing remnants of its near-supernova experience wreathe the star in the strangely-shaped, and strangely-named nebula we see today in the spectacular images taken by Hubble Space Telescope.

How the Hommunculus got its name

The nebula got its name when high-powered visual observations made in the late 1940s with a 61-inch reflector at Córdoba, Argentina, revealed that Eta Carinae was surrounded by a complex physical structure. In a 1950 paper in the Astrophysical Journal, Ernesto Gaviola, then the director of the Astronomical Observatory of Córdoba, described it as looking like a homunculus.

This 19th century engraving of Goethe’s Faust and a homunculus is how I have always envisioned the Homunculus Nebula

For the longest time I thought he meant that the tiny dark inclusions in the telescopic view of the nebula resembled a “real” homunculus – the tiny little humanoids the alchemists believed could be grown in a vial, the recipe for which the strangest alchemist of them all – Paracelsus, who wandered a meandering path of chemistry, philosophy and superstitious occultism in his quest for knowledge – provided in his 16th century work, De Natura Rerum:

“Let the semen of a man putrefy by itself in a sealed cucurbite [glass vessel] with the highest putrefaction of the venter equinus [horse manure] for 40 days, or until it begins at last to live, move, and be agitated, which can easily be seen. After this time it will be in some degree like a human being, but, nevertheless, transparent and without body. If now, after this, it be every day nourished and fed cautiously and prudently with the arcanum of human blood [its constituents known only to the alchemical fraternity], and kept for 40 weeks in the perpetual and equal heat of a venter equinus, it becomes, thenceforth, a true and living infant, having all the members of a child that is born from a woman, but much smaller. This we call a homunculus; and it should be afterwards educated with the greatest care and zeal, until it grows up and begins to display intelligence.”

The somewhere along the line I discovered Gaviola was describing it thus: ‘…a shape resembling a “hommunculus” with its head pointing northwest, legs opposite and arms folded over a fat body, could be clearly seen”.

I have to confess that when it comes to asterisms or the portrayals that nebulae depict, I’m a non-starter. As the devoted owner of a chicken named Camilla Corona, I have stared long and hard at the Running Chicken Nebula (IC 2944) and in no way can I see the chicken that everyone else seems to see so clearly. Likewise, no matter how long and hard I stare at the Homunculus can I see the fat little man Gaviola described (even Gaviola’s images in his paper in the Astrophysical Journal [Vol 111], in no way depict the fat little man to my eye, his descriptions notwithstanding).

But when I gaze at the amazing Hubble images – or even better, the image brought to me via my telescope – I see Paracelsus’ little homunculus being brewed up in a vial (although to be frank, until last night it was just the little double-rounded vial filled with its homunculus-growing potion I saw in my own telescope).

But that is the best thing about astronomy – you must take what the telescope (Hubble or otherwise) gives you. You can’t ask the universe to magically show you how an astronomer in the 1940s saw a nebula.

OBSERVING UPDATE – January 2, 2019

Image credit ESO

I regularly visit the Eta Carinae Nebula and its Homunculus. But last night’s view of the Hommunculus with the 16” was beyond description; intensely orange and so crisp and steady and detailed and entrancing that I was astonished when I discovered that two hours had passed while I swapped eyepieces and looked at it at every magnification possible.

It really is stunning at every magnification (130x, 228x and 333x). The incredibly bright, hazy, beautifully orange star shrouded in the middle, with its two dazzlingly orange lobes orientated SE-NW. The lobe to the SE is the bigger of the two and certainly the brightest – it is pretty circular, a little bit flattened on its SE end and with a tiny little bugle immediately SW of Eta, and it is radiantly orange – while the NW lobe is fainter, a more translucent orange, and very narrow where it extends away from Eta, opening out into the most elegant petal shape, with a beautifully round NW edge. The SE lobe has a subtle granularity to it and a magnificent clear dark inclusion that runs through the middle with an elegant little curl to the south at the end… the tiny little homunculus in his round cucurbite! 

The NW lobe shows no internal detail. The edges of the two lobes are beautifully clear cut and defined, and in moments of excellent seeing the outer periphery of the SW lobe has a slightly tattered look. The two lobes create notches near Eta and averted vision reveals a very thin, short almost spike-like tendril of orange nebulosity extending into the NE notch between the two lobes. I looked for, but alas couldn’t catch, a corresponding SW spike.

The entire Homunculus is surrounded in a faint, hazy, diffuse, incredibly delicate orange glow that appears to be evenly distributed around the whole object and that has no definite edges – it simply dissolves away into the sky

Talk about alchemy… a little diminutive being being brewed up in the furious expansion of a huge, billowing pair of gas and dust clouds. And shrouded within the brilliant cocoon, the famed eruptive star that will end its life in a blaze of glory when it blows itself to smithereens in a supernova – and when it does, we can expect a spectacular view from Earth as the little homunculus is blasted into the universe to enrich the next generation of stars.

Copyright © Susan Young 2017