To The Core, Part II

For more than a thousand years the Eagle Nebula – also known as the Star Queen Nebula, the Spire, Messier 16 or NGC 6611 – has been one of the most iconic deep sky objects in astronomy. Its overall shape and makeup, combined with some vivid and masterfully crafted visual images promoted the rise of astronomy to a popular science and gave the cloud complex its more commonly known name of the ‘Pillars Of Creation’. And what pillars they were! Jets and pockets of dark dust, called Bok globules, mixed with brightly illuminated stretches of nebulae, shaped like a veil by cosmic radiation and gravitational effects, have spurned the inspirations of many artists throughout the recent centuries. Needless to say, after having left the first waypoints of the expedition behind, the Eagle Nebula was a natural choice for the next couple of exploration targets.

With a bit more rationale though, the Eagle complex, much like any other of the bigger star forming regions, is a cloud complex consisting partly of thick dust clouds with molecular hydrogen (and some other elements) in them, which is the stuff giving birth to a new generation of stars. Those are the afore mentioned globules. Then there are less dense patches or ‘bubbles’ of ionized dust in which star formation cannot take place due to the heavy radiation bombardment from nearby massive stars. Together, they form a giant molecular cloud named IC 4703, so the Eagle Nebula is strictly speaking just a part of a much bigger object, and Messier 16 in truth is ‘just’ a dense cluster of stars embedded in all this. So, it’s beautiful, but it’s complicated. It gets even more complicated when a thousand years ago astronomers argued the Eagle Nebula should have been destroyed long ago by a supernova blast and that you would see the results only a thousand years later. Today, nothing of that theory remains: The Eagle Nebula is still there, albeit not in its most glorious days. Still, it’s a worthy sight to behold and an appropriate target for an in-depth survey. Thousands of years of x-ray radiation have taken its toll on the complex: The area is prominent with the short lived massive stars of the B-type, which over the million years burned away much of the gas around them. There is also the occasional neutron star but as mentioned, the nebula itself and the M 16 cluster nestled inside it are the dominant features here.

The Distant Worlds flotilla stayed for a couple of days in the area before moving further coreward towards the next waypoint, which was the NGC 6357 Nebula.

This large emission nebula is also known as the Lobster Nebula or the War And Peace Nebula. The latter name is rather fitting as the region is in constant turmoil. Most of the complex is considered a H II region of atomic hydrogen, which is the result of the heavily ionizing radiation of the most massive stars here. This radiation is ‘at war’ so to speak with the last thick patches of molecular clouds in which star formation still takes place and that are full of young protostars. This gives the nebula its rather torn and shredded but strikingly beautiful appearance. The nebula is also bigger than the Eagle Nebula, easily spanning a hundred light years across. There are several neutron stars at the verge of the complex, another testimony of the region’s active cycle of stellar birth and death.

Within the nebula lies the Open Cluster of Pismis 24, an OB association of roughly a dozen young and massive stars. In fact, the cluster is the cradle of some of the most massive stars having formed ‘recently’ (in astronomical terms). The reasons are still debated but most scientists assume that gas turbulences, magnetic fields and galactic density waves create a huge cocktail appropriate for birthing such massive stars. Pismis 24-1 for example was once thought to have no less than 300 solar masses until 21st century astronomers found out it was a trinary system. Or at least they thought they did. But even then the star system would be massive with both stars still packing more than 150 solar masses. With modern FSD technology, however, nothing was easier than to fly there and have a look, and it turned out Pismis 24-1 was in fact only a binary system with ‘only’ 130 solar masses. It shows how crude technology was developed in the 21st century or that astronomers supposedly were a drunken lot in those days. Whatever the case, the Pismis Cluster is worth an in-depth survey because of the amount of black holes and neutron stars and also because it is a prime example of mass segregation, where a cluster’s members are ejected into the stellar stream. This at least explains why Pismis’ massive stars are scattered that much.

The Distant Worlds flotilla once again allowed its members some time to explore the nebula and its surroundings. Alas, there is never enough time to see it all, and after three days the fleet moved on further coreward and traversed the Scutum-Sagittarii Conflux into the Norma Expanse. The next waypoint was the so-called “Hollow Veil”, a strikingly beautiful nebula just outside the galactic bulge in a region of space Universal Cartographics – for whatever reasons – chose to name “Blae Hypue”. Nobody knows what genius drove them but it is a clear sign that back in the day the telescopes of Messier, Herschel and Lacaille were just too primitive to make out  these jewels against the backdrop of the Milky Way’s center. So you won’t get any “proper” names for these deep sky objects anymore, and you will have to deal with it for the rest of your journey; well, most of it…

When you cross into the Norma arm and continue your travels towards the core a few things happen. The most apparent thing is that the stellar density is rising significantly.  It is hard to make out clusters or associations of stars without the proper tools. No, when you get near the bulge of the Milky Way, everything turns into a thick sea of stars. Furthermore, interstellar gas thins out sufficiently so there are no more “dark regions”. Thus, you get a relatively unobstrused view of the galactic center without very many dark spots or patches of black ink blocking the way. The next thing you may realize is that not only the stellar density increases but overall the stars get older. True, there are also many younger stars still born out of the surrounding interstellar medium but the overwhelming majority consists of older low-mass stars, and it will stay that way. It is here, right on the edge between the outskirts of the bulge and the gaseous turmoils of the Norma arm that the Hollow Veil Nebula lies.

The Hollow Veil now is a bright nebulosity of ionized hydrogen and possibly helium and oxygen. It has a wispy shape, almost like curtain sheets layered upon one another, hence its name. It is speculated that the different layers are the result of cascading supernova shockwaves rushing through the area, compressing and dragging the interstellar medium (mostly gas and dust) with them and thus giving them the shapes we see today. Apart from its ionized components the Veil also still holds enough interstellar matter to trigger the formation of new stars. An abundance of protostars and a couple of especially massive B-type stars supports this theory.

The Distant Worlds called a waypoint in one of the systems near the Veil, and like busy bees the explorers set off surveying the area. It all lasted for a day or two, before Exploration Command issued the next itineraries for the voyage, which would lead further coreward and deeper into the bulge of the Milky Way. There was much ahead and time to go.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s