MACHOs (Massive Compact Halo Objects)
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Basic Information

MACHOs stands for Massive Compact Halo Object. This proposed type of Dark Matter is basically just a catch-all for large bodies of normal matter that don't emit visible light.

Basically, a MACHO is just any large celestial body that does not produce its own light (or produces very weak light), and therefore is very hard to spot with a telescope. Here's a few possible MACHO types:

The "halo" part in the MACHO acronym refers to these sorts of objects being suspected to exist in the galactic halo - the mass of dark matter we can't physically detect at the edges of galaxies, but whose presence is strongly implied by the mathematics and physics of the way galaxies move. One theory is that there are a lot of these dark objects floating about out there beyond the stars. Recent data collected via the Hubble Space Telescope suggests that MACHOs account for less than 1% of the dark matter halo mass. If math concerning Dark Matter isn't flawed, then there must be some other form of Dark Matter out there. MACHOs may however account for 20% of the (non-halo) dark matter in our own Milky Way galaxy.

MACHOs could thus be a navigational hazard to spacecraft traveling at high speeds through the cosmos, especially those attempting to cross the immense void from one galaxy to the next via some form of FTL. Though such things are theorized to be found en masse at the edge of galaxies, individual MACHO-type dark objects can be found "drifting" through space well within galaxies as well. Clusters of MACHO-like objects might exist as well, either within or at the edges of galaxies, and these configurations are often known as RAMBOs.

Spotting the MACHOs

MACHOs in your path might not be noticed until you'd gotten relatively close, by which point you may have already built up a very large momentum in their direction and thus not have time (or thrust) necessary to avoid collision. Simply shining a spotlight ahead of you won't be good enough to allow you to spot some huge non-reflective rock in your trajectory at sufficient distance to turn away. It is also worth remembering that naturally-occurring objects in space often travel at very high speeds relative to one another. Just because there were no rogue planets on this route the last time you made this voyage doesn't mean that nothing could come along to surprise you. An uncharted planetoid whipping past you at thousands of kilometers per second can certainly ruin your day, even if it doesn't kill you.

Presumably most deep space voyages will be towards a destination star or other visible goal point, which may aid in the detection of any MACHOs close enough to your flight plan to pose a danger. From a distance, gravitational lensing may indicate MACHOs in a line between you and a bright object (such as a star) that you are looking at or heading towards. That is to say that the gravity of a large dark object in your path will actually bend the light beaming to you from the star, causing it to seem to "flare" or waver. The star might actually appear brighter because of something being between you and it, provided that something (a MACHO) had a large gravitational presence. The light would bend around it, and slightly more light would reach you than if the massive object weren't in the way. As you more closely approach the dark object, it will eventually resolve into a silhouette or eclipse-like image of a dark object occluding some portion of the more distant goal star. Depending on speed and power ratios of the spacecraft (and reaction time of the crew), waiting till the object is visible as a "shadow" in front of the star might mean again you're too close to dodge. Spaceships exploring uncharted regions of space may best be advised to spend as much time as possible heading directly towards bright objects so as to increase the chance of detecting any hidden MACHOs in the way by gravitational lensing.

See Also: RAMBOs


2. Non-Fiction Book: The Physics of Star Trek by Lawrence M. Krauss

Game and Story Use

  • See Interstellar Terrain, Navigational Hazard, and Dark Matter.
  • MACHOs can serve much the same purpose in a game or setting as asteroids do, but on a grander scale. You can mine them, hide behind them, crash into them, etc.
    • Most spacecraft that PCs will pilot through the void will have sufficient weaponry, shields, or maneuverability to deal with most asteroids. MACHOs however could be big dark hunks of rock just a bit too small to actually collapse under their own gravity and become a star. Most PCs in most settings probably won't have enough firepower to blow up a planet or star.
  • An encounter involving unanticipated MACHOs along the route could rely on the PCs rolling their skills of piloting, sensor operation, awareness, or just an initiative roll to be able to react in time. However that could essentially boil down to an all-or-nothing single roll that determines whether or not the campaign ends in an unexpected TPK. Since that's not likely to be much fun, the GM should probably be prepared with consequences other than "the ship crashes, and you all die". Here's a few other consequences you might consider:
    • Emergency landing on the MACHO. You're now stranded on an ice-cold dark rock, awaiting rescue. If it doesn't come soon (and the ship lacks suspended animation technology), we're back to the TPK scenario.
    • Emergency landing in some other nearby system.
      • Your ship limps to a port other than where you'd expected to arrive, and now must put in for repairs.
      • Robinson Crusoe style, you end up stranded on an uninhabited but resource-rich world in a nearby system. It's not as good as putting in at a friendly port, but it's better than dying in space. Can you survive on the untamed world long enough to make repairs or await rescue?
    • Damage, gravitational affects, or energy expenditures leaves the ship adrift in space, reduces momentum, or consumes most of the fuel. You're still heading towards your destination, but at a much slower rate. The trip takes much longer than normal, and the ship requires repairs or refueling once you get there.
  • MACHOs could form a "barrier" at the edges of galaxies.
    • As if the insanely large gaps between galaxies weren't deterrent enough to intergalactic travel, there could be a "wall" or "maze" of MACHOs to navigate before you could enter or leave a galaxy. Smacking into a MACHO at FTL speeds isn't a good idea.
      • In the real world, MACHOs are unlikely to be placed densely like the asteroid thicket of sci-fi films. (Then again, neither are asteroids.) Once properly charted or illuminated, avoiding the MACHOs shouldn't be too hard provided you fly at a reasonable speed. But the cinematic notion of everything being closely packed and smashing against each other is more fun, isn't it? So who cares if sci-fi writers have no sense of scale?
      • Clusters or formations of MACHOs are known as RAMBOs.
    • All those backwater worlds on the galactic rim might actually make good ports of call for deep space mining vessels that hunt the edges of the galaxy looking for MACHOs to strip mine.
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