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Dark Matter Discovered
sebFlyte writes "Wired is reporting that scientists have come up to a solution as to where all the matter in the universe actually is. Experiments being done with Chandra, NASA's X-ray telescope have shown up a likely candidate for the solution of the dark matter problem. There are massive quantities of Baryons in a super-heated gas cloud several hundred million light years away."
Which is what they're constantly doing. I heard the theories in my astronomy class. There's plenty of them, such as brown dwarves just drifting around out there. How do you explain them? Well some star has a vector or some light appears bent (lens effect) and it's figured there's some large enough object out there not emitting light which is doing it. And who's to say it isn't large amounts effectively of bits the size of pea gravel drifting around?
In other words, if regular stuff is about 5% of the energy density of the universe, with dark matter at about 20%, and dark energy at about 75% -- the stuff in this story comes into that 5%, ie, regular stuff and not dark matter.
Dark matter is, as I understood, matter which isn't emitting some radiation, i.e. visible light or gamma rays. It's predicted, because without something being somewhere a number would be +0.0000150 instead of +0.0000146 and we can pretty much drop the old Intel Pentium jokes.
A feeling of having made the same mistake before: Deja Foobar
First, I had to look up "tachyon". You are right, tachyons are apparently particles that travel faster than the speed of light. I've only heard the term from Star Trek, and for the time being that's where these particles are from - the realm of (science) fiction. I've certainly never had them mentioned in class!
Baryons are not the counterpart to tachyons. Baryons are simply particles that are made up of quarks. The two best known examples are neutrons and protons, which make up virtually all of the stuff you own. Yes, baryonic matter is pretty much everything we interact with.
Two examples of particles that are very common and all around us are electrons and neutrinos. You're familiar with electrons (which are not baryons!), and the nuclear reactions in the Sun are constantly producing a mind-boggling number of neutrinos. Generated in the centre, they travel at nearly the speed of light which means that the ones passing through your body right now are about 8 minutes old. By comparison, the light from the Sun (photons, also not baryons) bounces off all the photons there, so by the time it actually reaches you it's about a million years old.
Finally, and most importantly, dark matter has not been discovered. You are also right in that the reporter is very much out of his depth. The article states that there is evidence for baryons to be found in places where we have not seen them before. What's one theory as to how they got there? Dark matter.
I am an astrophysicist.
t ml#cosmologicalconstantproblem/.
What I was trying to point out, but evidently with little success, was that the article was hyping the discovery. It is certainly important (as you might gather from the fact that it is being published in Nature). The article, however, summarizes the physicists' findings but allows the reader to think that the "dark matter" that the article refers to is that really mysterious stuff that science fiction writers like to write about, not the less mysterious stuff that the physicists were actually talking about.
And, by the way, dark energy (which indeed is horribly named) is a huge mystery. Ask a particle physicist to calculate the vacuum energy density and he will give you an answer that is incorrect by many, many, MANY orders of magnitude. See http://www.site.uottawa.ca:4321/astronomy/index.h
Dark Matter isn't the only theory about why astronomical data doesn't fit theory. Another theory is called MOND, MOdified Newtonion Dynamics, and it postulates Newtons gravety theory might break down at astronomical distances (instead of inverse square it might be something else) A modified version of Newtons gravety creation have been created to fit the astronomical data, but there is no explanation about why the force of gravity should change over vast distances. There was an article in New Scientist magazine a few weeks back about how the guys behind the MOND theory think that there may be two types of gravity, and it might explain the discrepency in the location of the Pioneer probes.
That paper you linked did not sway me, in part because it was clearly written without an open mind. It uses phrases like "the only way to do X if you rule out Y is to theorize something clearly unreasonable" to make its points. If observations disprove one theory, it does not prove the only known alternative. It simply means that you should question some more of your assumptions to figure out what you missed.
Clearly not all matter is in stars, so if that is your definition, then some dark matter must exist. My BS subject refered to the theories that dark matter must be something undiscovered, because we can't seem to find enough to fit the Big Bang theory's predictions. I remain convinced that the percentage of dark matter necessary to make Omega equal to 1 does not fit with observation.
I don't pretend to know what the correct theory is, but I am convinced that the Big Bang is not accurate, and that there are forces/processes at work in the cosmos that are being thrown out prematurely because they contradict the Big Bang, thus preventing the most accurate theory from surfacing. Ned Wright's defenses and criticisms are not the open-minded evaluation that I was looking for.
--Sandy
2. Several ways --- rotation, motion of a number of satellite galaxies, mass/light ratio, Tully-Fisher relation, and, if it's a spiral, simply by the size if we know the distance (this is pretty rough, but a decent indicator)
3. Within a galaxy, I don't think so. But intra-galactic dark matter is just one type. There is also non-luminous matter in between galaxies in clusters to account for their motion. Hot X-ray gas is one candidate, but I thought I remembered that there didn't seem to be enough of that stuff to account for cluster dynamics. Maybe this new stuff will help out, though the mass deficit was much more than this 2% if I recall correctly, and is probably non-baryonic.
3. Yes, they should. That's the problem. Outer stars and globular clusters are orbiting way to fast if all the mass in the galaxy is traced by luminous matter. A good model to account for the rotational behavior is a spherical halo (not just a disk) of non-luminous matter. This is the intra-galactic dark matter, and not relevant to the article.
Actually, it is well established that the dark matter is NOT baryonic.
The story is a bit about dark matter, because there is a dark matter presence implied by the newly discovered gas clouds. But that's no surprise - the observed structure of ordinary galaxies already implies that they as well are permeated with dark matter.
Cosmologists, primarily based on data from the Wilkinson Microwave Anisotropy Probe, are now willing to put pretty hard numbers on the ratios of baryonic and non-baryonic matter (about 1:7 or so). ALL of the non-baryonic matter is dark. A good fraction of the baryonic matter is dark, in the sense that it doesn't emit much light (e.g., very cool stars, non-accreting black holes, planets, etc.).
There sure is dark matter out there that we don't understand well at all, and probably more than one kind. Neutrinos are one form, since recent experiments indicate they do have some mass. Neutrinos are pretty exotic compared to normal baryonic matter. There may well be weirder stuff.
Agree with you though, that Star Trek overdoes it.
Professor of Astronomy, Author of Spider Star & Star Dragon (Tor)
I'm an astrophysicist, too, and think we've crossed paths here before. I'm also a science fiction writer, and I'm exploiting some of the exotic, non-baryonic dark matter for my second novel (under revision now, working title is SPIDER STAR).
While we have some ideas about the non-baryonic dark matter that might pan out soon, indeed, we're clueless about the dark energy in a very profound way.
Professor of Astronomy, Author of Spider Star & Star Dragon (Tor)
a, but there is no explanation about why the force of gravity should change over vast distances.
:~D
YOu gotta admit, though... There really isn't a good explanation of why gravity SHOULDN'T change over vast distances.
F=ma = G*M*m/(r^2) -- 'G' is derived observationally. Only a few hundred years of observation tell us that it is a constant. Only a few dozen of those actually FROM SPACE -- Perhaps a few hundred years more will show that it is proportional to some (presumambly negative) exponent of 'r' (distance). Perhaps not.
I admit to preferring MOND over imaginary matter. However, what I like the most is that the guys have open minds... unlike the typical 'scientist' favoring NB matter -- a bad hypothesis usually treated as sound theory. If NB matter were treated with the caution that MOND is, I would enjoy reading about it. Instead most authors treat it as assumed fact and build upon it. Bah. Excel can curve fit data; doesn't mean I assume a random scatter plot can be modeled by a 4th order equation.