Wednesday, September 28, 2011

Flames and Hot Gases

The Flame Nebula we saw in class is distinguishable from other nebula because, unlike all others, it looks like a fluorescent blob.

But if you look carefully it looks like two cells splitting, likely in anaphase, with little microfilaments around them.

In a month or two we'll be able to see this nebula in Orion (visible with the 3 stars forming his leathery belt).

We see beautiful bright glows and a stunning dark silky patch in the middle of the Flame Nebula. The dark patch - just non-emitting gas and big dust particles - is simply ISM (Interesting Stuff in the Middle, or interstellar media?) covering the glowing gas behind and absorbing incoming light.

The colors in any nebula are understandable with a little bit of chemistry. A nebula is an aggregate cloud of hot gases. Nearby stars light up these gases with UV radiation, ionizing the (often) hydrogen atoms to a higher energy state; as the atoms fall back to a lower energy state they recombine with electrons and emit light, hence emission nebula. This constant of flux is excitation, relaxation, and recombination leads to a continuous emission of the bright colors. From high school chemistry and the Balmer series we remember that the red emissions are due to hydrogen, which dominates most nebula. The Flame Nebula however is dominated by green and blue, which indicates that helium and heavy elements, like iron, have also been ionized. The blue-green colors of the nebula suggest that the proximity of high energy sources, because it is difficult to ionize heavy metals.

The little tendrils of milky clouds extending out of the nebula are dark clouds of dust and gas we see (barely!) because they reflect blue light from, again, nearby stars. Blue light is reflected most because it is reflected most efficiently (dark regions have dust particles about a micron thick, roughly the size of the blue wavelength). This is the same reason the sky here is (usually) blue, except on Earth nitrogen and oxygen are doing most of the reflecting.

The allure of the Flame Nebula is that it has a central emission nebula embraced by a darker reflection nebula. There's a lot to say about just the dark gases in the nebula, but that's for another day. I wonder who'll be around to see the stars born out of this giant.

1 comment: