Saturday, January 23, 2016

I am the Alpha and the Omega

Where the Lagoon Nebula was already an eyecatcher, I was most eager to find out more about one of the jewels on my 'To Visit' list: The Omega Nebula, also named the Swan Nebula or just Messier 17. In fact, from the Lagoon you can already get your first glimpses of the Omega Nebula, a distant and darker hue of gas against the plane of the Milky Way. You will also see the bright, young stellar cluster of NGC 6618, which was born out of parts of the nebula in the not-so-distant past.

The Omega Nebula is thought to hold some 800 times the mass of Sol. That is no biggie for a nebula, mind you, but those parts of the Omega Complex that we don't see hold some 30,000 solar masses more. This makes the complex one of the most massive ones on our side of the galaxy; and it also gives you an idea about the complexity of those interstellar gas clouds. In fact, the complex is nearly identical in its makeup when compared to the Orion Complex in our immediate neighbourhood. We just see it at a different angle from Sol.


The area around the nebula is a so-called H-II region, a region dominated by ionized atomic gas. This ionization comes from the nearby cluster of massive, young stars, namely NGC 6618. Their radiation is so intense that it tears atoms apart and makes the surrounding gas heat up and 'shine'. So when we see the Omega Nebula, we only see an illuminated hotspot within a much bigger cloud of gas and dust. Again, it gives you an idea about the size of these interstellar cloud monsters.

When talking about the young star cluster of NGC 6618 we are talking about a former part of the Omega Complex that somehow collapsed and gave birth to a multitude of protostars (both T Tauri and Herbig Ae/Be stars) and young main sequence stars, including a few O types. They should now be in the process of using up the remains of the cloud core's gases and eventually drift away. For the interested explorer, there are quite a few very interesting objects to be surveyed here. The most massive stars seem to have collapsed already so there are quite a few neutron stars and black holes hidden in the cluster. Especially the stars of the PW2010 survey seem to hold most of them and they are awesome to behold and sometimes quite hazardous to navigate.

Scanning down all of the NGC's stars would obviously take a huge amount of time and would warrant an entire expedition in its own right, so I made a mental note on coming back at a later time. It's not like those stars are going anywhere soon, their expansion rate is estimated to be merely 12km per second.

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