There's an extremely high amount of variation in All of Known Existence. We do see many many stars, with an extensive amount of evidence for planets orbiting around stars. However, is there are way to determine whether or not there's something like a 'dark solar system'? That's the only thing I can think of to call it.

This would be made out of a central body of mass, where the majority of material is located, with smaller planet-like objects in orbit around it, not unlike Pluto and its satellites.

Well, what about nearly-massive-enough-to-be-stellar objects? Why would there not be more of these - and the inevitable satellites involved in something of that mass - than there are solar systems?

I'm also assuming these would be made out of the same material that nearly everything else is, and I would expect them to be in abundance, so, could this explain the dark matter mystery? Assuming these dark systems are made out of the same - or mostly the same - material, wouldn't that also mean that spectral analysis wouldn't be able to determine if light from stars passed through the dark systems?

Intuition tells me someone has already debunked this, but I haven't been able to find an answer one way or the other. (yet)


2 Answers 2


You're asking two related but distinct questions here:

  1. Well, what about nearly-massive-enough-to-be-stellar objects? Why would there not be more of these - and the inevitable satellites involved in something of that mass - than there are solar systems?

and also

  1. I would expect them to be in abundance, so, could this explain the dark matter mystery?

For the first question, astronomers have studied for a long time the question of how many of each type of star (and substellar object) form. More precisely, from a given cloud of mass, how often do you form 10-solar-mass stars, 1-solar-mass stars, 0.1-solar-mass stars, 0.05-solar-mass brown dwarfs, etc. The overall distribution is called the initial mass function, or IMF. It has been clear for a long time that massive stars are less common than low-mass stars. So there was a question, similar to yours, of whether the fraction just keeps going up as you go to lower and lower masses. But it is only in the last 10 years or so that technology is good enough for us to have relatively complete survey of these dim, low-mass objects. And those have shown that the IMF does turn over (e.g. here), that there is some (low) stellar mass that is the peak, and that as you go to even lower masses than that, stars start to become less common at those masses. So that's how we know that brown dwarfs aren't more common than stars - we've looked! They are detectable, especially when young - they're just really faint.

As for #2, James K already gave a good answer there. The only thing I'd add is that people have also searched for MACHOs directly, using gravitational microlensing. If they were super common (i.e. common enough to make up the dark matter halo), they would frequently pass in front of stars in the Magellanic Clouds or in the Andromeda Galaxy, causing those stars to brighten briefly. Studies that have looked for that see occasional events (telling you that the technique works), but not nearly enough to account for any substantial fraction of the dark halo. Note that this technique doesn't require the objects to emit any light at all, so it is sensitive to very old brown dwarfs in the halo, which would be hard to detect directly in the solar neighborhood in the kind of study I described in #1.

  • $\begingroup$ Thanks for that. I was unaware that there was enough data to demonstrate that higher mass stars are more common than low-mass ones. That's what you're saying, I'm understanding that correctly? $\endgroup$
    – Facey Neck
    Aug 1, 2020 at 21:57
  • $\begingroup$ No, just the opposite. Higher mass stars are quite rare. If you take 100 stars at random, there’s a good chance that none of them would have spectral type O or B, the two most massive and hottest types: astro.uu.se/~ulrike/Spectroscopy/PPT/Spektraltypen.GIF I was trying to make a secondary point, that even though M type stars (the lowest mass stars) are the most common, we now know that the trend doesn’t continue beyond that, and that brown dwarfs are less common than M stars. $\endgroup$ Aug 1, 2020 at 23:54

Brown dwarfs (ie sub-stellar objects that are too small to support hydrogen fusion) do exist and some brown dwarfs have been found to host planets. An example of this is the brown dwarf 2M1207. It is a very dim object, about 25 Jupiter masses. It is still quite hot, so not completely "dark", and it hosts a planet with a mass of 3-10 Jupiters.

There are doubtless other similar bodies, and smaller rogue planets with moons, though such bodies would be very hard to observe. Light would rarely pass through such a system (the gaps between systems are just too great) but if it did, the gravity of the system could cause light to be focussed. This is called "microlensing" and is an observed phenomenon.

The idea that such bodies could explain dark matter is a good one, and it has even been given a name "MACHO" for "Massive Compact Halo Objects". The trouble with the MACHO hypothesis is that it doesn't fit with our understanding of how matter forms after the big bang. If matter behaves how we observe to behave, then there is no way that the big bang could have created enough normal matter to explain the observed amount of mass, this means that the excess mass must be in some other form, perhaps as a "WIMP" (Weakly Interacting Massive Particle) And yes the names were chosen to mirror each other.

We seem to live in a universe dominated by WIMPs and not MACHOs.

  • $\begingroup$ Thanks for your input as well. There's one thing I'd like further expanded: If I'm understanding you correctly, these 'dark solar systems' can and do exist, and are incredibly difficult to detect, but our current understanding of The Observable Universe would suggest that these objects cannot be in abundance, and so if they are, the models would be incorrect? $\endgroup$
    – Facey Neck
    Aug 1, 2020 at 22:00
  • $\begingroup$ It is hard to make a model that 1. creates enough regular matter for MACHOs to explain dark matter. 2. Isn't contracdicted by observations of particles at CERN, and 3. Isn't contradicted by observations of microlenseing and the large and fine scale structure of the Universe. Our best cosmological models include WIMPs. $\endgroup$
    – James K
    Aug 1, 2020 at 22:26

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