Thursday, 16 December 2010

Red Banana in the Milky Way

Look what a gorgeous project the Zooniverse has started!

Aren't they beautiful?

These are nebulae in our own galaxy, imaged with the Spitzer Space Telescope and now at the mercy of the zooites - so I have the feeling our entire galaxy will be mapped out in more bubbles than a bubble bath soon.

Remember the barred spirals lecture at Astrofest nearly two years ago? Johann Knapen mentioned then that Spitzer was an infra-red telescope (its webpage says it is designed as such; the lecture, from what I remember, seemed to imply that it could once do shorter wavelengths but its telescope has now warmed up too much to cope with that). I never heard more about the mapping of bars - mind you, we did our own bars project in the end. Anyway, this very same telescope is imaging nebulae in infra-red light - the kind of radiation that we sense as a feel of warmth on our skin.

Not nebulae all over the sky, I should point out. Mostly in towards the plane of our galaxy - the fuzzy pale band you'll see in dark clear skies. It's often impossible to pick out any stars in it because there are so many of them, including a general build-up of distant ones too far away to make out individually but whose collective light stains the sky. (Isn't it infuriating? I tried to find a remotely realistic, recognisable picture, but it's impossible - all of them are ridiculously fancy and long-exposure. Would any relatively normal photographers like to remedy that . . . ?) But that's where most of the nebulae are.

Not all matter is confined to stars. That which floats freely, within galaxies and outside, is not just dark matter, either. A lot is gas, which, if allowed to cool enough, provides fuel for star formation. Ironic that it needs to cool to form such hot things, isn't it? That's because heating gas up makes it fly all over the place - and in order to clump, the atoms and molecules need to be still, close together, and undisturbed. Where enough gas or dust is present to block or scatter light, or indeed to emit its own light, that's a nebula.

There are a great many types of nebula, which I think I'll leave to another blog post; you can check out Hubblesite for an overview. What the Milky Way Project is looking at is those involving star formation.

Stars initially form coccooned in dark gas; their births are therefore invisible to us, mysterious, though we are learning to see through their shrouds. The Pillars of Creation are a well-known example. Here they are as the world knows them:

. . . and here they are at the Milky Way Project:

But once they start shining, their solar wind blows off the remaining clouds, leaving a bubble like this:

This is the same thing as the solar wind that our Sun creates - a constant thin but powerful wafting of hot charged particles, which extents pretty much halfway to its neighbours (and which Voyager is leaving round about now). It's these charged particles that cause the aurora - and why, without a magnetic field to divert or otherwise channel them, planets such as Mars make biological life difficult on the surface.

(The Aurora over Noway. From, as ever, APOD.)

The Milky Way Project FAQ - a very informative page! - reports that the green and red parts of bubbles are different. In fact, you'll notice that the pictures are mostly red and green. The green light is 3 to 8 µm long - this is, on a logarithmic scale, only just longer than visible light, visible red light being about 0.7µm. The red light is a lot longer and therefore coming from weaker-energy (colder) sources - 24µm.

Different materials emit radiation in different, very specific wavelengths. That means, of course, that two different materials are being looked at. Zookeeper Rob (a.k.a. Orbiting Frog, and an exceptionally amiable person!) explains here that red is general warm dust, such as tiny silicon particles; and that green is polycyclic aromatic hydrocarbons. Do you remember those hexagonal carbon-based molecules from chemistry, where we were first taught to write two lines on alternate faces, and then not to? Polycyclic aromatic carbons are large structures of these, looking a little like strips of chicken wire. Actually if you click the link and scroll down you'll see a sight now getting familiar . . . These are effectively "soot" from stars - star formation bellows out as mixed a bag of by-products as cigarette smoke, but these complex carbon molecules fluoresce in ultra-violet light. Hot young stars of course will produce plenty of this (its wavelength is just a little shorter than visible light, just as the infra-red Spitzer is seeing with is a little longer). So they're an excellent general gas tracker. Zookeeper Chris's current non-Zooniverse research involves star formation and the use of sulphur compounds to track it - they are another good tracer.

I mentioned earlier that gas needs to cool in order for gravity to shrink it and start starforming, for heat and light and stellar wind from stars generally throw things around everywhere - that's why red spirals shut down, as we discovered two years ago. One mystery the Milky Way Project is hoping to solve is why the dust doesn't seem to be being blown around as much as it should be: why is it still there? But knowing what the Zoo projects are like, I bet a large host of unexpected and possibly even un-thought-of questions end up getting answered too!

For example, here's something I found as one of my first images: what is this red banana?

"Some warm gas I think," replies Rob. "A classic, if oddly shaped, fuzzy red object." Damn! Oh well. Only a few get lucky at once. Science is fruitful, but it usually takes a while . . .

Ooops! Once the bad jokes start it's time to get my coat. Please hop aboard, draw bubbles, and join the discussion!


Nas said...

They are all such AMAZING pictures! And in the picture showing the 'Pillars of Creation' on the far right, it looks like there is a dog leaning against one.

Thank you for sharing.

Sakib said...

Ever since I got interested in astronomy, nebulae have been my favourite type of deep sky object! They're so colourful and they really stir the imagination and childlike wonder! These infrared images are of a type of nebula known as emission nebulae, they form stars as well as dark nebulae. I love infrared images of star forming regions as they show such cool things that can't be seen in the optical wavelength as their light is blocked by great clouds of dust. My favourite infrared images are of jets ejected by young pre main sequence stars, you can see lots of great images on the website of the professional astronomer Chris Davis: