31 October 2016 | A Giant Squid in Space!

OU 4

Credit & copyright: Nicolas Outters | Click image to enlarge

Image Data
  • Location: France
  • Date taken: 11/07/2015 – 7/08/2015
  • Camera: Moravian G4
  • Optics: Newton SV400 F3,8
  • Mount: Paramount ME I
  • Filters: Astrodon Ha/OIII 3nm + RGB
  • Exposure: 138 x 600 H-Alpha, 107 x 600 OIII, 13 x 60 x RGB (x3). Total: 42(!) Hours

In the deepest and darkest depths of space resides a nebular denizen of the cosmic population of the waters of the Milky Way flowing through the constellation of Cepheus! With the terrifying moniker of the Giant Squid Nebula, the existence of this gargantuan gaseous beast was brought to the attention of the world only recently.

Also known as Ou 4, this is one of a number of planetary nebulae discovered in deep astrophotography by the French amateur astronomer Nicolas Outters. Discovered in 2011, its presence only became apparent after long OIII exposures equalling 12.5 hours were taken of the emission nebula Sh2-129. Spanning a little over 1 degree from tip to tip, Ou 4 is believed to be a bipolar outflow but conflictingly the possibility it is a giant nearby planetary nebula or other type of eruptive mass loss cannot be ruled out at the moment.

Considering the impressive morphology of this nebula, it has understandably evoked the imagination and excitement of both professional and amateur astronomers around the world! With its dramatic appearance, studies by professionals were carried out immediately after its discovery with an explanation for its existence being sought out. Their answers have been mired in confusion with the truth being far from conclusive. This current state of confusion is a combination of the difficulty in determining distances of multiple elements as well as the extreme faintness of Ou 4.

From an outward perspective, the bipolar structure appears to surround the bright star HR 8119 being situated roughly near its centre. However when observing the universe, appearances can be deceptive, two objects being near each other in the sky doesn’t necessarily imply that they are physically associated in space. Recent distance determinations have established that HR 8119 is responsible for ionizing the red emission nebula Sh2-129, which suggests both must be located at the same distance of 2300 light years. As well as being located at the centre of Sh2-129, HR 8119 is also situated near the central part of Ou 4. Another interesting piece of the puzzle is that HR 8119 is a triple star system!

The complex structure of Ou 4 consists of a few loosely defined bubbles and limb brightened bowshocks at the tips of the bipolar lobes, which are composed of complex filamentary arcs. The overall morphology has been compared to the peculiar planetary nebula KjPn 8, which appears to have an outflow based structure. Analysis of the gas has led to the “shocking” revelation that the gas in the lobes is ionized by shocks presumably generated by it colliding with the surrounding ambient gas of the HII region. Furthermore, the velocity of the lobes are symmetrically aligned with both HR 8119 and Sh2-129 further strengthening their association with each other. The bipolar lobes measure 47×8 light years and might represent a 90,000 year old outflow ejected by HR 8119.

Ou 4 will continue to be studied by professional astronomers in the future and as time progresses, the proper motions of the lobes will be able to be measured, thereby providing an accurate determination of its distance. If its distance is equivalent to Sh2-129, then this would very likely suggest it is an outflow. If its distance is much closer than Sh2-129, then this would support the planetary nebula hypothesis, which would make it the largest known planetary nebula as well as one of the closest! Currently the closest known planetary nebula is Sh2-216 at a distance of 420 light years.

On the threshold of visibility, the Giant Squid Nebula represents an excellent “challenge” object for amateur astrophotographers! Unfortunately it is not possible to observe it visually due to its intense faintness. In the past decade, amateur astronomers have made a large number of planetary nebula discoveries with one of the most well known and significant being the Soap Bubble Nebula by Dave Jurasevich. In the past few years, numerous discoveries have been made by dedicated French amateur astrophotographers. The increase in amateur discoveries is due to a variety of reasons including improved sensitivity of commercially available CCD cameras and filters. However the main reason is amateurs having the freedom to obtain very long exposures of many hours. Professional astronomers are usually allocated limited telescope time at professional observatories, which is also expensive and highly competitive. As time progresses, more new and unknown nebulae will be discovered by both amateur and professional astronomers!

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