 Hidden Matter W.I.M.P.'s Neutrino's UnknownThe missing mass problem is another one of those many problems that are puzzling astronomers everywhere. The missing mass problem exists because measurements of the mass of the universe and measurements of the energy output in the universe disagree. When measured and compared, it turns out that we can only see about 10 or 20% of the entire mass of the universe, leaving us with a lot of "dark matter". Now, if you watch any of the Star Trek series, you may notice that they tend to refer to dark matter as this mystic, invisible substance that they run into on occasion. That is not entirely the case. Dark matter actually comes in a few different forms. Gute Dachbeschichtung im Hessen . ffs machine Hidden Matter The first form is simply matter that we can not see. Brown dwarfs, although fairly massive, (just a little smaller than the smallest stars) let out very little radiation, and are very difficult to find at any long distances. However, they are believed to be very common, and can account for a portion of the missing mass in the universe. White dwarves, which tend to be more massive, do glow for up to a few million years after there creation, but after that dim into obscurity. They can also account for some of the missing mass. Neutron stars, which are even more massive, with at least 1.4 solar masses, are never very bright, and in fact they don't produce electro-magnetic radiation at all (with the exception of pulsars). The only way we can find them is by their interactions with other stars. W.I.M.P.'s The second form comes in the form of W.I.M.P.'s, or Weakly Interaction Massive Particles. (Just as a side note, this is another thing I like about astronomy, when we name something, we don't give it a confusing and hard to pronounce Latin name, we give it a nice, descriptive, english name) Now, as the WIMP's name might imply, the are very massive (as sub-atomic particles go), and the interact very weakly. WIMP's are believed to be, as I said, sub-atomic particles. They don't actually participate in the electro-magnetic force, only gravity and the weak nuclear force (along, possibly, with the strong nuclear force). They have no magnetic properties, and no electric charge. The electro-magnetic force has absolutely no effect on them what so ever, and vice versa. Photons aren't reflected or absorbed by WIMP's, they simply fly through them as if they don't exist. Consequently, there is no way to see them. Also, they are much more massive than the average proton or neutron, probably by at least a factor of 100. Although this isn't a very massive individually, they are believed to exist in great enough numbers to more than make up for that fact. Because of these properties, WIMP's act a lot like neutrinos. Neutrinos Now, although I will talk about neutrino's significance to missing mass, first, I am going to talk about neutrinos in general (just giving you fair warning). For a while, neutrinos were another one of those little things that had scientists everywhere shaking their heads. However, they have recently begun to give up their secrets. Neutrinos are small particles with little mass. They are electrically neutral and have very little mass, so generally they are unaffected by other objects. They are produced as a by-product of nuclear reactions. They were originally discovered when precise measurements revealed that a very small amount of energy was lost during nuclear reactions, and couldn't be accounted for when the mass and energy of the byproducts was measured. And, according to laws of conservation of matter and energy, this wasn't possible, so it was believed that it was being carried away by a particle they couldn't detect, which they later named a neutrino (I believe it's Latin or italian for "light ones", or something to that effect). The problem came with detecting these. Even though they are produced in impossibly large numbers in the sun's core (a few trillion have probably flown through you as you read this paragraph), they are unaffected by mass and simply fly through it. Neutrino detectors (which we have managed to create, I will get to that in a minute) work just as well during the night as they do during the day, because the neutrinos easily pass through the earth! Obviously, creating a neutrino detector wasn't a very easy thing to do. Finally, however, it was done. Neutrino detectors are simple in design but hard to make. For starters, all neutrino detectors have to be buried deep in the earth, to make sure only neutrinos can reach there (if it were near the surface, cosmic rays and other forms of radiation may skew the results). The majority are buried in the deepest mines there are. Although neutrinos rarely ever react with anything, they do come by the trillions, and they do react in some ways with some things. One of the first detectors was simply a giant container filled with hundreds of gallons of a special cleaning fluid. When a neutrino interacted with one, it would interact with the atom of cleaning fluid via one of the nuclear forces, changing it's composition and making one of the byproducts radioactive. Then, once a month, they would count the number of radioactive atoms, which told them how many reactions had occurred. They initially expected about 12 a month, which tells you just how little neutrinos interact, since trillions would fly through that tank every second. However, they only had 3 or 4. Since the numbers of neutrinos expected was calculated very specifically given the conditions inside the sun's core, this meant that we either had something wrong about our knowledge of the sun, or something else was happening. Eventually, the problem was discovered. It turns out that there are 3 different types of neutrinos, electron neutrinos, tau neutrinos, and muon neutrinos. Originally it was believed that neutrinos were mass less, however, it was eventually discovered that they weren't, and that would allow them to change back and forth between the 3 types of neutrinos. Then they realized (or already knew) that neutrino detectors were only detecting one type of neutrino, the electron neutrino, which explained it. One of the approaches in more modern detectors is hundreds of gallons of ultra pure water. Although the reactions per month is the same, when a neutrino interacts with a water molecule, it let's out a flash of light, which is easier to detect than a single atom in hundreds of gallons of fluid. Now then, back to neutrinos and missing mass. Neutrinos weren't originally considered for the missing mass problem, because they were believed to be mass less. However, with the discovery that they have mass, even if it isn't much, is significant because of their very large numbers. The exact mass of a neutrino hasn't been pinned down yet, so we don't know exactly how much of the missing mass they account for, but they do probably account for a fairly large percentage, considering their extremely large numbers. Every single nuclear reaction in the sun produces a neutrino, so given the rate of fussion in the sun, is a very, very large number. Multiply that by all the stars in the sky, and you have a lot of neutrinos. Unknown Now, although between them, those three factors do account for a good portion of the missing mass in the universe, if they accounted for all of it, missing mass obviously wouldn't be a mystery. I think there are one or two more explanations that I haven't heard of, but even those don't solve the problem. The remainder of the missing mass in the universe is unacounted for, for the most part, we don't know what it is, or anything about it. It could be some form of matter, even more mysterious than WIMP's, or it could simply be inaccurate calculations, due to the fact that we simply can't measure the mass of the universe as accurately as we may want to. It's just another one of those mysteries waiting to be solved. |