Wednesday, August 24, 2011

And Now For A Real Brown Dwarf

This is cool (pun intended). I love astronomy - I'm not a professional astronomy anymore than I'm a professional scientist, but I have studied up on the matter and I took a class in college, which is better than what most people can claim. This discovery is interesting to me on multiple fronts. The first reason this is interesting to me is because I'm an amateur science fiction author, and I have a strong desire to be accurate in my portrayal of how the real world works. The second reason is because I only recently learned what brown dwarfs were, and the thought that there might be some nearby excites me. Allow me to start by explaining what exactly a brown dwarf is, before I move on.

A dwarf is a star that doesn't set on the main sequence of stars. All stars follow a set life expectancy because of their size; the largest stars live shorter but they have wilder lives because they burn though their fuel (the hydrogen in their core) faster. Live fast, die young. These stars are called Supergiants, and there's even class above them called Hypergiants. Now, those aren't really on the sequence either, but set off to the side - I brought them up because it's useful to know what's playing opposite of dwarf stars.

Your main sequence stars are each given a letter. That letter reflects where they fall on the Hertzsprung-Russel diagram:

That's an older example of the diagram, shown before the discovery of Hypergiants. Here's what a Hypergiant looks like:

That yellow dot is the Sun. Earth wouldn't even register. That star is easily several AU in size, probably extending well past the inner belt and into the Outer System.

Anyway, the diagram is lettered. The first letters are O, A, and AB. These are usually called "White" stars. White stars are exceptionally hot. These are some of the hottest stars on record, but they tend not to live very long, because they are so hot and they do burn through their hydrogen. The next stars are F and G stars. F stars are hotter and shorter-lived than G stars, but longer than O, A, and AB. F-type used to be referred to as "Green," but anymore, you'll see "White-Yellow." A G-class star is a middle-of-the-road star. Our own Sun is a G-type; a healthy G2 star. If there's likely to be life, it'll probably be on planets orbiting around G-type stars. G-type are called "Yellow" stars. The next letter is K. K is a much cooler and smaller star that's called "Orange." Stars that come smaller than K-type stars are called dwarfs. There's a couple different qualifications for dwarfs: M-type, which is a red dwarf, is the most common type of dwarf, and indeed, possibly the most common type of star, in existence. Red dwarfs are very cool, very small, and last for a long, long time. D-type dwarfs are called "White" dwarfs. White dwarfs burn hot but they do so for a while. They're hot and heavy; in a system with multiple stars, the other stars are probably orbiting the white dwarf. The next type of dwarf is called a "black dwarf." Black dwarfs are theoretical; they're what happens when a white/red dwarf runs out of fuel and eventually "blacks out". Because of how long these stars last, though, it's hard telling whether or not it's possible or if they just move onto a new state.

The last type of star is the focus of this post. They're classified L through Y type, with L-type being the "hottest" in a relative sense and Y-type being the "coldest". These are failed stars - they didn't have enough mass to sustain nuclear fusion in the core and as a result, they didn't flare up and become stars. They're called "brown dwarfs."

To the untrained eye, brown dwarfs resemble exceptionally large gas giants. There was some debate over whether or not Jupiter is actually a brown dwarf; I'm not sure if that's still going on or if it's been settled. But Jupiter is the closest thing we have in our system to a brown dwarf, unless you ascribe to the Nemesis theory, which states that somewhere out there is a companion to the sun (probably an M-type star, although given this article, it may very well be a brown dwarf), that comes along every so often and messes up stuff in the Oort cloud, causing a rain of comets into the inner system that pelt the inner system planets.

As far as we know, M-type stars are the most common type of star. At least, that's what we think. A recent discovery, however, has perhaps thrown this into doubt: an ultra-cool brown dwarf has been discovered. By ultra-cool they mean one that burns at room temperature - 86 degrees F. While that might not seem cool, figure most stars burn anywhere from 6,000K to 40,000K (72,000 degrees F, for those keeping score at home). 86 degrees seems like paradise compared to those numbers.

While that's cool itself (the prospects of colonizing that surface? Probably slim. I bet it still has a killer electromagnetic field. If Jupiter is anything to go by, several minutes of exposure to Jupiter's electromagnetic field is more than enough to kill a full grown adult - the moons/planets might be habitable, though. Io doesn't have an active core - it's kept alive by the pull of Jupiter's gravity. Likewise, Europa's oceans are kept warm in the same manner. It's easily possible to imagine that one of those moons could be kept active through tidal action), it has far, far reaching consequences:
Two new brown dwarfs have been discovered relatively close to to our solar system. Spotted by astronomers from the Leibniz Institute for Astrophysics Potsdam (AIP), the "failed stars"* are only 15 and 18 light-years from the sun.

15 and 18 light-years may not seem that close -- after all, the nearest bona fide star to the sun, red dwarf Proxima Centauri, is a mere four light-years away. But if these discoveries continue it may not be long until a brown dwarf, and not Proxima, is found to be our nearest stellar neighbor.
Basically, these things are so cold and so dim that they slip past the radar on the initial sweep. In fact, they might slip past it on the third and forth sweep. However, if we're surrounded by brown dwarfs, and these ultracool brown dwarfs are the norm, and not an exception, this means that brown dwarfs could supplant M-type stars as the most common stars (or, rather, failed stars*) in the universe. It also means that there could be brown dwarfs near us. If there is a brown dwarf within, say, 2ly, it's not a stretch to assume it would have moons (hell, look at Jupiter, Saturn, Neptune or Uranus. They weren't content with "just moons," oh no, they have whole effin' solar systems to themselves. Saturn has something like 97 moons and counting). If those moons are anything like Europa (another stretch, but not unreasonable given how Europa operates and how similar Jupiter is to a brown dwarf - with the exception being that brown dwarfs are much, much larger and thus, much, much more active), then what we might have here is a launching point for interstellar missions. It's a long shot, but it's worth it. And if the brown dwarf burns at 87 degrees at the cloud tops, then why not send some floating cities down and colonize it there? We could do that on Venus; why not try building a real Cloud City?

I'm a dreamer and none of those will probably work. But I haven't heard anyone suggest it, and it's okay to dream every so often. Nobody does it anymore.

* Or, if you'd rather be positive, you could call them "over-achieving Jupiters."

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