N144 – A Starry Superbubble

8th Oct 2018

N144 imageSir Isaac Newton’s famous metaphor for how knowledge progresses, “If I have seen further, it is by standing upon the shoulders of giants” is one of the most frequently used quotations in scientific enquiry, alluded to by researchers of all backgrounds who wish to acknowledge their own limitations when faced with the complexity of their subject. Because of the access we have to the discovery, observation, description and cataloguing of every glorious objects we see through our telescopes, I often feel as if I am peering over the shoulders of giants as I sit at my telescope… and especially so during my observation of the superbubble, N144 in the Large Magellanic Cloud.

Writing a blog on Pietro Baracchi and the Great Melbourne Telescope (GMT) around the same time I was reaching N144 in my superbubble re-observation project had put the GMT squarely in the forefront of my brain. A reflector telescope with a speculum mirror of 48 inches in diameter, the GMT was erected in 1869. At the time it was the second largest telescope in the world and the largest in the southern hemisphere. From the date it was erected until 1885 it was devoted chiefly to a revision of the Southern Nebulae observed by Sir John Herschel at the Cape of Good Hope in the years 1834 to 1838.

Imagine my delight when browsing the “Observations of the Southern Nebulae made with the Great Melbourne Telescope from 1869 to 1885” for the Baracchi blog, I came across Joseph Turner’s December 1875 sketch of N144’s NGC objects – 1962, 65, 66 and 70 – that he had made using the Great Melbourne Telescope! (Turner was employed at the Melbourne Observatory as Assistant Astronomer, from 1873 to 1883, and during this period was the main observer to work with the Great Melbourne Telescope.)

 

Joseph Turner's sketch of NGCs 1962, 65, 66 and 70; the Great Melbourne Telescope The person depicted is believed to be Joseph Turner, who was employed at the Melbourne Observatory as Assistant Astronomer, from 1873 to 1883, and during this period was the main observer to work with the Great Melbourne Telescope. The photograph was taken between these two dates, and most likely during the earlier part of the period around 1875.

Joseph Turner’s sketch of NGCs 1962, 65, 66 and 70, and a circa 1875 photo of the Great Melbourne Telescope … the man  in the photo is believed to be Joseph Turner. Image credit Museums Victoria

Of the complex, Turner notes:—  “The several patches of this group are not at all so regular and well-defined as in H.’s sketch. The number of small stars here is very great, and their light almost hides the nebula. The three n.f. patches are so very thickly studded with very small stars that it is difficult to see any nebula at all, and except upon a very clear night none could be seen; at present the sky is very clear. The s.p. patch has no stars in it, and is very like as H. shows it — round, and gradually brighter in the middle. H.’s sketch shows only about a dozen stars, while at present the entire area embraced by the several patches is glittering with stars, mostly very small, with a few of about the 11th to 13th magnitude.”

In 1882 he states:— “The lithograph represents pretty fairly the present appearance of the group, except that the second preceding patch is shown much too distinct and bright, it being in reality very faint and ill-defined.”

According to the publication, “The eye-pieces generally used were No. 1, 2, or 3, whose powers are respectively 234, 280, and 330”, which made me very curious as I headed out to the telescope with Turner’s sketch and notes in order to peer over his shoulder and see what I could see with my 16″ Dobs (powers of 130x, 228x and 333x) of what he had seen with the 48″ GMT. (Albeit Turner may not be considered one of the giants of astronomy, the telescope he was looking through certainly was and he had the observational skills to both see and record its revelations.)

 

This annotated DSS image showcases N144's starry delights

This annotated DSS image showcases N144’s starry delights

 

Albeit visually beautiful and fascinating N144 is, compared to some of the Cloud’s superbubbles, a relatively simple superbubble in the eyepiece – a semicircular complex made up of a few almost blister-like H II regions surrounding a central cavity. The 390 x 245 light year sized superbubble was blown by the young OB association LH 58 and, as always, that was where I began.

Without a filter…

I have looked at N144 uncounted times yet this night, that telescope, peering over Turner’s shoulder… it IS a starry superbubble!!  “… the entire area embraced by the several patches is glittering with stars, mostly very small, with a few of about the 11th to 13th magnitude…” Clearly he could see a hell of a lot more stars with 48″ than I with 16″, but LH 58 really is a beautiful star cloud that glitters in my eyepiece with a handful of scattered stars and heaps of that very particular starlight that teases with unresolved stars just beyond the scope of one’s equipment and eyes, although relaxed and wandering averted vision pulled out lovely little poppers that briefly sparkled into view and then disappeared. I really longed for 48″ of aperture in order to appreciate – “The three n.f. patches are so very thickly studded with very small stars that it is difficult to see any nebula at all, and except upon a very clear night none could be seen…”

The open southern side of the cavity holds a particular delight… three Wolf-Rayet stars! Brey 34 is a beautiful bright white mag 9.8 star… just gorgeous in both its appearance and its location and indeed its very being… a massive star reaching the end of its short but blazingly brilliant life (who can’t enjoy seeing these chaps, never mind ones residing in another galaxy?) Brey 32 is a mag 12.3 star, while Brey 33 glows at a less than brilliant mag 14.77.

I followed my way around the NGCs to see their stars, starting at NGC 1970, which consists of three close stars oriented NNW-SSE. The brightest, a mag 10.8 star lies at the northern end; a mag 13.2 lies at the southern end and a mag 12.4 lies in the centre. the centre of this crooked little trio of stars seems immersed in a small smudge of unresolved starlight.  NGC 1966 appears as a gathering of a few faint stars with numerous tiny stars popping in and out of view, especially with averted vision. NGC 1965 appears as a couple of faint stars floating in a bed of unresolved starlight, with only a further two or three that pop in and out of view (or it might be the same popper, it’s actually quite hard to tell). NGC 1962 is the prettiest of the four NGC’s with a half a dozen faint stars speckling its nebulous glow and a number of very small stars darting in and out of the unresolved starlight. Looking at Turner’s sketch out at the telescope, it was really interesting to notice how differently he, seeing so many more stars than I could, saw NGC 1962 compared to to how I was seeing it. Unlike his two distinct groupings of stars, I saw it as one gathering of stars somewhat extended NNE-SSW and dusted pretty evenly with stars.

Without a filter, N144’s nebulosity appears as a faint uneven semi-circular mistiness in which the NGCs 1962, 65 and 66 are embedded as brighter patches of glowing mistiness studded with varying numbers of small stars. The nebulosity peters out before it reaches NGC 1970, but its stars complete the semicircular shape. The edges of the superbubble’s nebulosity are superbly non-existent… it all just seems to dissolve away into the surrounding starry background without one able to really define where. Very lovely!! Peering over Turner’s shoulder, I really I get his “The number of small stars here is very great, and their light almost hides the nebula. The three n.f. patches are so very thickly studded with very small stars that it is difficult to see any nebula at all.” Although all I can see is a scattering of faint stars, the swath of the superbubble’s semicircle literally scintillates with unresolved starlight, and across the breadth of it very small stars pop in and out of view with averted vision. (It reminded me of a fantastic expedition I went on with a beekeeper in the Western Cape to his really remote hives, one group of which we had to walk through the fynbos to reach – from afar the hives looked like small patches of whiteness from which I could now and then pick up a bee popping in and out of view. The only difference of course… we could walk up close and see them all!! And as an aside, at one of the hives I got to hold the bloated queen bee with her little retinue of helper bees in the palm of my hand; what a thrill!!)

The superbubble’s nebulosity responds well to the UHC filter and one certainly can see the superbubble’s circular shape in the  nebulous semicircle. As a whole the semicircle is awash with a faint nebulosity upon which are superimposed the brighter NGC patches. NGC 1970 is revealed to be surrounded with a very faint haze. NGC 1966’s nebulosity is a small, bright, even, irregularly-shaped glow surrounding the stars. It doesn’t have sharply defined edges, but one can most definitely see where its edges fizz out into the faint surrounding nebulosity. NGC 1965 is also a small bright irregularly-shaped even glow, smaller than NGC 1966, but with similar fizz-out edges. And the easternmost NGC 1962 appears as a lovely, large, fairly bright hazy glow. It is also irregularly-shaped and its edges are less distinct than NGCs 1965 and 66, but still  distinct enough to clearly demarcate it.

All-in-all, a lovely evening peering over the shoulder of a giant.

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