Author: Tammy Plotner

Out in the deep reaches of space, a cocoon has formed. Here on Earth, a cocoon represents the casing of a pupae – the child/insect which is about to undergo a magnificent transformation into a beautiful moth or butterfly. So what does the cosmic cocoon, IC 5146, hide inside? Let’s take a look…

Roughly 4000 light years away in some of the richest star fields in the northern Cygnus Milky Way, lies IC 5146. Discovered by Thomas Espin, it has often been referred to as the “Cocoon” because it lay at the end of a long and fairly starless trail – like the proverbial worm who ate its way to the end of the leaf before time for change. Although IC 5146’s fanciful name fits wonderfully with its visual appearance, what you may not know is the moniker is also very indicative of the star-birth process going on inside!

Deep within the folds and rifts of the bright nebula are many regions of emission, absorption and reflection. According to studies done by Kramer (et al), “A submillimeter dust continuum study of a molecular ridge in IC 5146 consists of at least four dense cores which are likely to be prestellar in nature. A map of dust temperatures, constructed from the continuum flux ratios, shows strong temperature gradients. Several cores appear isothermal, while two have inwardly decreasing temperatures profiles, which is expected if the cores are externally heated. We find an inverse correlation which we interpret as signature of grain coagulation and the formation of ice mantles, in accordance with models of dust evolution in dense prestellar cores.”

The embryo is emerging stars.

According to recent measurements, the massive star in the center of the Cocoon opened its way into the existing molecular cloud – the flowing and glowing region also known as Caldwell 19. Even though the central star is perhaps 100,000 years old, it still provides the major energy source of the visible light – but what about what is invisible?

According to W.B. Samson: “The very young star cluster IC 5146 is studied using star counts, with a view to determining the distribution of interstellar matter in a region where star formation recently occurred. IC 5146 is embedded in a dark nebula which is very dense near its center.” A dense center which hides magnetic properties! “Polarization of starlight in IC 5146 is found to be very variable in both magnitude and direction, indicating the presence of complex magnetic fields within the cluster.”

While the dark dust trail of Barnard 168 may appear to be full of nothing – nothing could be further from the truth. According to Lada and Elmegreen: Millimeter-wave observations of the dark cloud complex immediately surrounding the young open cluster IC 5146 show two unusually intense oxygen sources… suggesting the presence of two or more obscured newly formed stars embedded in molecular gas at the periphery. The total mass of the dark cloud complex is estimated to be 2500 solar masses, and the origin of the star-forming molecular shell around IC 5146 is considered. It is noted that IC 5146 is located at the tip of an elongated filamentary molecular cloud and, in this respect, is similar to Rho Oph and M17, where regions of active star formation are also located in dense cores at the tips of elongated molecular cloud complexes.”

The 10th magnitude Cocoon is easily revealed in mid-sized telescopes and can be found near Pi Cygni (RA 21 53 6 Dec. +47 16) and M39. Capturing this rare transformation is definately worth your time, for open cluster Collinder 470 is also ‘involved’ with IC 5146. Take the time to look it up! Small reflection nebula Van den Bergh 147 is also nearby and adds another treat to this comsic chrysalis!

This week’s awesome image was contributed by Advanced Optical / Radio Astronomers and International Associates member Tom Davis. Thanks for the spectacular image!

Over the weeks we’ve taken a look at some very curious objects which have often raised some wonderful questions. One such question dealt with what could be observed should a supernova event involve a planetary system. In this case, it’s not quite the explosive mass destruction scenario – but a planetary nebula that consumed its planets…

Veteran sky observers have long been aware of the unique structure of planetary nebula NGC 7008. Located about 2800 light years distant in the constellation of Cygnus, report after report shows even amateur telescopes easily resolve out the central star and unusual bright areas in the outer shell. We might wonder about it when we see it, but what lay within is quite unique.

Because the central star of NGC 7008 is so prominent, the original lines of thinking on this nebula’s formation focused around the central star itself. Says Francesco Pala: “Much of the recent attention on primordial stars has focused on the properties of massive objects, considered the natural outcome of first structure formation. While there are reasons to believe that massive stars were common, but not unique, in the early universe, the question of their actual formation is still not adequately understood…. how unique must have been the physical conditions in primordial clouds to yield such an unusual distribution of stellar mass.”

In 1995, the Hubble Telescope was pointed towards NGC 7008. The primary aim of the survey was to find close, resolved main-sequence companions of the central stars, which through main-sequence fitting would provide excellent distance estimates for the nebulae. What they found was only the beginning of the end.

Scientist Mario Perniotto studies planetary nebulae and their gas dynamics. “I first recall the history of PNe which are generated from low and intermediate mass stars through successive mass loss processes starting in the Red Giant phase of evolution and continuing also after the termination of the pulsed AGB phase, where most of the nebular mass is believed to be ejected. The corresponding stellar winds are the ingredients of the nebula. Their initial properties and subsequent mutual interactions, under the action of the evolving stellar radiation field, are responsible for the properties of the nebula.” Through studies with the Hubble, the kinetic structure of NGC 7008 has been observed to have another unusual feature – Fast Low Ionization Emitting Regions.

Says Perinotto: “Attention is focused on FLIERs and on the proposed mechanisms to interpret them. Recent observations with the Hubble Space Telescope have provided us with a wealth of detailed (subarcsec) information on the nebular structures. The inner structure of FLIERs is here illustrated to consist of substructures of various shapes with an high degree of individually from object to object, also within the same planetary nebula. These new data call for deeper theoretical efforts to solve the problems of cosmic gas dynamics, posed by their observed properties.”

But the motions of the gas aren’t all that’s being observed – the dust itself plays an important role. According to studies done by Klaas and Walker, some of NGC 7008’s dynamic structure comes from dual layers of radically different dust which originated from two different sources. Could this be the result of a binary star taking its last twin breath? First the older star… And then the younger? Says Tylenda and Gorny: “Therefore we can conclude that the H-poor layers in these stars have been exposed shortly after the PN formation at the tip of AGB. This excludes, from our considerations, scenaria like that of a final helium shell flash which produced a H-poor, He-burning nucleus surrounded by an old, large nebula.”

But astronomer Noam Soker wasn’t taking that for an answer. “For NGC 7008, a deviation from symmetry is expected and indeed a departure is observed, but the main signature is on the outskirts of the nebula, and hence an interaction with the ISM (interstellar medium) is possible. If the companion is associated with the PN central star, as claimed… I put a question mark, since it is not clear if the morphology is compatible with the claimed companion or is solely due to an interaction with the ISM.”

Enter the Instituto de Astronomía in México. “We suggest that some of the structures observed in the envelopes of planetary nebulae are caused by the interaction of central star wind and radiation with preplanetary nebula debris: planets, moons, minor objects and ring and ring arcs. Recently considerable amount of planetary material has been reported to exist around solar type stars, this debris could be evaporated during the envelope ejection and alter the chemical abundance and produce some of the envelope inhomogeneities. If there are massive enough rings of material surrounding the progenitor and planets in their vicinity, arc rings could be formed. If the rings are viewed pole on when the envelope is detached from the central star, it will interact with the arc ring material and produce ansae and pedal and garden-hose-shape structures observed in some planetaries.”

Next time you visit NGC 7008 – take a closer look like Dr. Dietmar Hager did. There’s something more to this story than just another pretty cosmic face. Something he recognized and asked me to investigate. Not only does his image reveal the presence of FLIERS and the well resolved central region, but a structure that’s made scientists look again and again over the years. Of all the explanations and science that I’ve researched, I like Noam Soaker’s answer best:

“I propose that the destruction of brown dwarfs and massive planets inside the envelopes of asymptotic giant branch stars can lead to the formations of jets and ansae in elliptical planetary nebulae. Thick disks with jets on their two sides are the plausible outcome of this process. The process is likely to occur at late states of the AGB, and the jets push their way out of the envelopes in the course of a number of year. The Roche lobe overflow continues for several hundred years and destroys the secondaries. This scenario predicts that the same material will be contaminated by two sources. Once source is the AGB cores, from which material can be mixed into the jets and the other consists of the destroyed secondaries.”

Always look twice and think about what you’re observing… Because there is so much more there than what meets the eye!

These awesome images were done by Avanced Optical/ Radio Astronomers and International Associates member Dr. Dietmar Hager from StarGazer Observatory. Many thanks for the investigative challenge!

For those of us old enough to remember riding on an old fashioned carousel, there was once a quaint custom where the operator would hold a brass ring out and the lucky contestant who captured it could ride again for free. Before you dismiss this astrophotograph as just another colorful look at a Messier, perhaps you better step inside the workings of the merry-go-round to learn more about what you’re really seeing here… Because this ring is pure gold.

Discovered by Antoine Darquier de Pellepoix in January of 1779 and independently discovered and cataloged by Charles Messier just a few days later, the famous comet hunter himself described it as being “a dull nebula, but perfectly outlined; as large as Jupiter and looks like a fading planet.” Perhaps it was that very description which coaxed Uranus’ discoverer – Sir William Herschel – to have a look for himself and class such objects as “planetary nebula“. Fortunately, Herschel’s telescope resolved M57 to a far greater degree and his descriptions were “a perforated ring of stars… none seems to belong to it.” Since that time, astronomers have been turning an eye towards this “curiosity of the heavens” in a great effort to not only understand its cause – but to capture it as well.

In 1800, German astronomer Friedrich von Hahn was the first to resolve out the Ring’s central star – a planet-sized white dwarf variable star which has an average magnitude of 15. At one point in its Mira-like life, it began shedding its outer layers in what we now believe to be a cylindrical shape and what we see is the bright torus of light from our point of view. Of course, none of this is particularly new news about the 2,300 light year distant M57. Nor is the knowledge when we are looking down this tunnel of expelled gas that we are seeing a decreasing ionization level as the distance from the central star increases. For all who have seen the Ring with their own eyes the innermost region appears dark – the result of only ultra-violet radiation. What we can capture visually is the inner ring, glowing brightly with the greenish forbidden light of doubly ionized oxygen and nitrogen. Where the true prize lay is much like a carousel – it’s just outside where only the red light of hydrogen can be excited.

In 1935 an astronomer named J.C. Duncan discovered something a bit more about the Ring than we knew – an extended halo of material which is all the remains of the star’s earlier stellar winds. It took the power of the Hubble telescope to resolve out dust filaments and globules, but now I invite you to take a closer look at which took 40,000 years in the making and spans 500 times the size of our own solar system.

It took Dr. Dietmar Hager a full month of work to compile some 12 hours of exposure time to reveal what you see here, but the results from StarGazer Observatory are nothing less than amazing. Like the Hubble Telescope images of M57, this image reveals small clouds of dark dust which have flowed out from the central star and are captured in silhouette against the glowing walls of the planetary shell. According to what we know, “These small, dense dust clouds are too small to be seen with ground-based telescopes, but are easily revealed by Hubble.” What’s more, the outer filaments only recently came to public light as ” The Spitzer Space Telescope’s powerful infrared vision detected this material expelled from the withering star.”

Congratulations, Dr. Hager. You have managed with a 9″ Earth-based refractor to capture for us what took two space telescopes to first reveal – along with a distant background galaxy in the full sized image. At least in my book, that means you’ve done far more than just reach for the brass ring…

You’ve captured pure gold.

Over the weeks we’ve looked at a lot of curious objects and today is no exception. NGC 6302 is often called the “Bug Nebula”, but its resemblance to an insect isn’t what makes it unique – it’s the complex structure. Deep inside this bipolar planetary nebula lay an unseen star… One of the hottest objects in the galaxy.

Residing about 4,000 light years away in the constellation of Scorpius, NGC 6302 is the end remains of an enormous dying star. With a surface temperature of an estimated 200,000 K, its central star exceeds our own Sun’s mean temperature output by nearly 35 times – yet has never been observed. Why? Because it is shielded from view at all wavelengths by an impossibly dense equatorial disc composed of gas and dust… One that may have restricted the star’s outflow into the unusual bipolar structure we can see.

But the hidden central star isn’t what’s bugging scientists, it’s the chemical composition!

Filled with ionization walls, edges and lobes, this dust is both oxygen and carbon-rich – a dual chemistry which means it has undergone recent changes and alternate formation processes in its 10,000 year life. Studies done by the European Space Agency’s Infrared Space Observatory (ISO) have shown that the dusty torus contains hydrocarbons, carbonates such as calcite, as well as water ice and iron. If the word carbonates made you raise an eyebrow, it should because carbonates form when carbon dioxide dissolves in liquid water and forms sediments.

Says Albert Zijlstra from UMIST: “What caught our interest in NGC 6302 was the mixture of minerals and crystalline ice – hailstones frozen onto small dust grains. Very few objects have such a mixed composition.”

Yet NGC 6302 is even more complex, displaying evidence that a second pair of lobes may have formed during a previous phase of the star’s mass loss. The visible northwest lobe is believed to have been created some 1,900 years ago and shows some signs that it may have once collided with pre-existing globules of gas which changed its outflow. According to studies done by Groves, Doptia, Williams and Hua; “We find that for NGC 6302, the visible to IR extinction law is indistinguishable from `standard’ interstellar reddening, but that the UV extinction curve is much steeper than normal, suggesting that more small dust grains had been ejected into the nebula by the PN central star.”

Kinematical studies done by Minkowski and Johnson suggest that NGC 6302 originated in some type of explosive event. It exhibits a rich spectrum of lines, indicating rich deposits of helium and nitrogen – far more than an ordinary planetary nebula. What the Bug Nebula seems to lack in its diet, however, is iron and calcium – two elements which may very well be tied up as solid grains.

So what’s next for this extreme, high-excitation planetary nebula? According to Wright, Barlow, Ercolano and Rauch; “We use the 3D photoionisation code to model the emission from the gas and dust. We have produced a good fit to the optical emission-line spectrum, from which we derived a density distribution for the nebula. A fit to the infrared coronal lines places strong constraints on the properties of the unseen ionising source. We find the best fit comes from using a 220,000 K hydrogen-deficient central star model atmosphere, indicating that the central star of this PN may have undergone a late thermal pulse.”

But don’t you be late observing the Bug Nebula yourself! NGC 6302 is located in Scorpius (RA 17 13 44 Dec -37 06 15). At around magnitude 9, this surprisingly bright planetary is well within the reach of a mid-size telescope and a treat to larger aperture. NGC 6302 was discovered by James Dunlop in 1826 with a handmade reflecting telescope he had constructed himself and the earliest known study of NGC 6302 is Edward Emerson Barnard who, in 1907, drew and described it.

Seek it out… And enjoy!

This week’s awesome image was taken by Don Goldman from Macedon Ranges Observatory.