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Rocket your D&D 5E and Level Up: Advanced 5E games into space! Alpha Star Magazine Is Launching... Right Now!

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Message: <blockquote data-quote="fuindordm" data-source="post: 2703948" data-attributes="member: 5435">Well, I work in the field and I haven't heard about that.It's true that we don't know what it is, although we've been chipping away at the problem: it's reasonably certain now that neutrinos have a little mass, which will contribute a few percent of the missing mass.  Recent telescope surveys of our galaxy have turned up a larger population of brown dwarf stars (things more massive than Jupiter, but less massive than the sun, which burn very dimly and for a long long time) than was expected, and it's likely that such objects also contribute a few percent.  That still leaves a big chunk of 'cold dark matter' unaccounted for, which is likely to be an exotic stable particle that we haven't discovered yet because it can only be created at energies higher than what we can produce in the lab.  There is no shortage of candidates for such a particle, believe me!There are also lots of people out there that believe no such particle exists, and that a modification of our theory of gravity is needed to explain the motion of galaxies.  But no one is saying that galaxies are moving as they should given our current understanding of gravity and the tally of visible matter.In galaxy clusters, for example, the galaxies are zipping about at hundreds of kilometers a second.  When we add up all the mass in galaxies and hot gas (visible in the X-ray band), we find that these speeds are well above the escape velocity of the clusters.  Conclusion: if there were no dark matter, the cluster would fly apart and disperse in short order.  Since we see galaxy clusters everywhere and over a wide range of distances, this doesn't make sense.  What does make sense is to conclude that there is about three times as more mass in the cluster than what we can see.  If we do this then the galaxies and hot gas obey perfectly the laws of gravity as we understand them.  The hot gas in particular is very useful, because it fills the entire volume of the cluster and its temperature and luminosity decrease as you get farther from the center.  One can actually map out the gravity well as a function of radius this way.What has been recently debunked is the idea that the total amount of matter in the universe (dark or otherwise) is just enough to stop the expansion of the universe, which was the prevailing theory (for reasons of elegance) for a long time.  But this just means that we need less dark matter than was previously thought--the current observations have cut the amount of matter needed to 30% of this magic number.Cheers,Ben</blockquote>

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