Astrotropes: Space Clouds

Have you ever watched Star Trek II: The Wrath of Khan? If not, you probably should. Whether or not you’re a fan of Star Trek generally, it was probably one of the best sci fi movies ever made. Fast paced and full of action, it’s an easy movie to watch and one with all the excitement and emotional high points in all the right places. But there’s one part of this film in particular which I’m going to focus on here…

One of the movie’s final scenes sees Kirk and Khan piloting their respective starships into the midst of a nebula, where a rather epic game of cat and mouse ensues. Or cat and cat, more accurately. This was probably one of the first times a movie director paid attention to, and made use of, the fact that space is three dimensional and space ships can travel “up” and “down”. Since then, the space cloud theme has been used in many other sci fi scenarios. But would a space cloud like this really exist somewhere?

Well, actually, yes. In fact, the technical name for these things is literally “interstellar cloud” and a handful of us astronomers actually research these things. Interstellar clouds come in a huge variety of shapes, sizes and colours. Unfortunately, most of these wouldn’t really work quite like they do in the movies, on account of them being so huge it’s difficult for your imagination to do them justice. The Orion Nebula, for instance, so nearby that on a dark night you can see it quite clearly with your own naked eye as the sword hanging from Orion’s belt. In fact, the Orion nebula is around 1300 light years from side to side. It’s so big that our solar system would be like a speck of dust by its side. There’s also the small problem that while we see a dramatic nebula, by Earth standards, there’s practically nothing there. Even though it’s one of the densest parts of space, it’s still a harder vacuum than we can create here on Earth. Another space ship could be a couple of light years away and still be clearly visible!

So we need to look at smaller scales. The image to the right here shows a set of Bok Globules (these particular ones are found in the Pac Man nebula). Bok globules are another type of interstellar cloud, and they’re actually much smaller. Only around a light year across, these are cold, dark, and dense objects. Some bok globules are amongst the coldest natural places in the Universe, while others contain warm pockets where stars are forming. Somewhere within a bok globule may be a better place for Kirk and Khan to play hide and seek in their space ships. Sadly though, it wouldn’t be quite so exciting cinematically. These are dark clouds, without a lot of colour. Interestingly too, clumps of the interstellar medium (ISM) are believed to range in size down to the scale of astronomical units. Solar system sizes. These are actually quite an active topic of research, known as ISM small scale structure.

So even smaller still? As clouds like bok globules collapse, you start to get first hot molecular cores, then protostars forming. Actually, the Orion Nebula is full of these! In fact, the film clearly shows what’s technically known as a swirly thing. Swirly things in astronomy usually happen when stars form or die. So perhaps the final battle from Star Trek II might have taken place in or around a protostar. It would likely be dense enough to make things difficult to see. Also, a major plot point in the movie was sensor interference, and clumps of warm, dense interstellar material like this tend to emit quite brightly in radio frequencies. Even the dramatic lightning effects may not be as silly as some might expect. I’m fairly certain that high energy processes such as lightning have been hypothesised in some circumstellar regions before.

So all in all, if you want to have a tense starship duel, head for the nearest protostar and you might find just what you’re looking for!

A trope is a recurring theme in any narrative which conveys information to the audience. These are snippets of information which have somehow ended up in our collective subconscious as ways in which storytellers have gotten their points across. Overused tropes end up as clichés.

Images: Bok Globules in the Pac Man nebula from the Hubble Heritage Archive, Screengrabs from Star Trek II: The Wrath of Khan are © Paramount Pictures and used here in accordance with fair use policies.

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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