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Dark Matter Stars in the Early Universe?
OriginalArlen writes "UniverseToday reports new research which suggests dark matter could have condensed to form 'dark stars' in the early universe. These stars would have been very massive and burned very slowly, fueled by non-fusion reactions, they could still be with us. Astronomers hope to better constrain theories of early galaxy and star formation with observations of gravitational lensing events caused by these ghosts of the primordial universe."
Here is the PDF: Dark matter and the first stars: a new phase of stellar evolution
Here is the abstract:
As a matter of fact, there are several experiments looking for dark matter from the sun. Yes, there could be some dark matter loosely bound to the sun's gravitational potential. I can not give a comprehensive list here but a good example is CAST . There are other dark matter experiments which may be sensitive to a signal from the sun such as CRESST and CDMS.
Ok, so say you are not a physicist, you can still read the article. It may have equations, but it is still English: http://arxiv.org/PS_cache/arxiv/pdf/0705/0705.0521 v1.pdf
The authors say: "The nature of the cold dark matter in the universe is as yet unknown. Weakly Interacting Massive Particles (WIMPs) are possibly the strongest candidates, as WIMPs that were in thermodynamic equilibrium in the early universe automatically provide the appropriate relic abundance to give the observed matter density. More- over, WIMPs have a natural origin in particle physics, e.g. neutralinos in supersymmetric models are excellent DM candidates. [..]T he details of the interactions and masses of the neutralinos depend on a large number of model parameters. In the minimal supergravity model, experimental and observational bounds restrict the neutralino mass m to 50 GeV-2 TeV, while the annihilation cross section v lies within an order of magnitude of h vi = 3 × 10^-26cm3/sec (except at the low end of the mass range where it could be several orders of magnitude smaller). "
So the authors make it clear that they are working under a set of assumptions, which are now fairly well accepted in the astrophysics community. Yes, maybe, these set of assumptions are wrong and if they are, their nice constructed dark stars would not exist.... If the annihilation cross section was very very high, then all dark matter would have self-annihilated by now. So there are bounds on that. Yes, it is theoretically possible still, I suppose, that dark matter may not self-annihilate! That makes it harder to detect! Most favored particle physics phenomenology would suggest that there should be some annihilation cross-section, on the order of magnitude suggested by the measured strength of the weak-forces. It turns out that this annihilation cross section is low enough that most dark matter would have survived to this day after the ~14billion history of the universe.
dark matter is only special in that we can't "see" it. It not luminous or outputs so little energy that we don't have the equipment to detect it. It may not be anything more special then normal matter that doesn't glow. Perhaps it's just really low albedo matter like black dust.
There are theories about it being either this or special exotic particles or a mix of both. Your assuming it's all exotic particles.
"There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy."
Note that dark matter is *not* regular matter. It is matter which does not interact through the electro-magnetic forces. It does not interact "with charged particles" nor with light! Hence, the name "dark." If light can not scatter from it, then that makes it "dark."
An Arxiv paper doesn't really "count" as a publication for most purposes and certainly will not prevent you from "perishing" (that's what the peer-reviewed scientific journals are for).
Publishing in Arxiv is more like posting to a blog or slashdot where you semi-formally share your ideas and try to start up a discussion on the topic of interest to you.
Of course, some of the papers over there ended up being darn important.
Obama likes poor people so much, he wants to make more of them.
No, this is not an anti-matter star. Anti-matter is the "opposite" of particles that we are accustomed to, but still have the same interactions as the normal particles around us. So yes, they interact electro-magnetically. Say, you were a human being made of anti-matter on an anti-matter earth, in the part of the galaxy dominated by anti-matter, all visible physics laws would look the same. (Yes, there are one or two very weird experiments that would yield the opposite results. Feynman discusses this in his books, if you are interested.)
There are 4 forces, as we know it, in the universe. Gravitational, electro-magnetic, strong and weak. All these forces treat anti-matter pretty much the same way that they treat matter. Dark matter is something completely different. The reason is, it does not interact electro-magnetically. We know this cause we can "see" that it does not interact with photons( light )-- the force carrier of the electro-magnetic force. All observations agree that it does interact gravitationally. And whether or not it interacts weakly or not is under contention.
The significance of the results of dark matter experiments is very high. So, we pretty much, by now, know that dark matter exists and it does account for a large fraction of the energy budget of our universe, about ~22%. Good old normal matter accounts for about 4% of the energy budget.
Dark matter particles are probably flowing through you read this. They are around us. They interact only very very weakly and so we dont "feel" them. As their concentration is not very high, they do not contribute to our weight either. But they are around us, that's pretty clear.
If you think all this dark matter stuff sounds crazy, well, then a little factoid. About a billion neutrinos are passing through your eye-ball per second! They are mostly coming from the sun! And they flow through us, with extremely low probability of interacting, and with no real effect on our daily lives. Actually, the probability that ONE neutrino has interacted in the body of an 80-old person in his life time is about 50%. So that's a pretty rare event. The interaction of dark matter particles are on the same order of magnitude. For sometime, people thought that neutrinos could be dark matter candidates, until experiments showed that neutrinos are not heavy enough to account for ~22% of the energy budget of the universe.
So what does this whole thing mean? Dark matter particles are heavy particles, which do not like interacting with normal matter particles and mostly go about their own way, but still make their presence be felt, through gravity by structuring the universe through their overwhelming-numbers.
No it isn't. Spiral galaxies don't rotate like fixed plates. The spiral arms are density waves moving around galaxies and the rotation period of a star around the center of a galaxy varies with distance from the center of the galaxy. I don't know what astrophysicists need to do, but I do know that /. readers could do without people just making stuff up and trying to pass it off as science.
Doesn't it make you feel good to know that our freedoms are protected by politicans, lawyers and journalists.
That is incorrect
The theory is that immediately after the big bang, matter and antimatter began to annihilate. The asymmetry is explained partially through CP-Violation. There are other theories such as axions (which could be a form of dark matter) that may explain the remainder of the asymmetry.
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The idea that the net sum product of the Big Bang is 0 (zero) mass and energy is old, and has been discarded for better theories.
Except that's not exactly right. Matter and antimatter annihilate, true, but they produce energy as the product of that annihilation. So it's not exactly a zero-sum-game as you seem to think. You may be getting confused by vacuum flux (a real phenomenon that has been experimentally observed), in which pairs of virtual particles and anti-particles are spontaneously created in a vacuum, only to disappear without a trace when they collide again. In that case, you end up with nothing (unless you're talking about a region of space arbitrarily close to the event horizon of a black hole -- that's how Hawking radiation works).
Try "never." The current standard model in cosmology posits that matter and antimatter were created in nearly equal quantities which condensed out of the energy of the Big Bang. The resultant mass reacted with itself, and the energy produced by these annihilations generated the next wave of particle creation. Eventually, a very slight bias in the production of matter vs. antimatter led to the overwhelming dominance of "normal" baryonic matter in the visible universe.
The idea that there are vast pockets of antimatter out there in the universe has been generally discarded. As for why there was a bias toward "normal" matter and against antimatter, I don't think that has ever been adequately explained, although there are several competing theories. It's interesting to note that in quantum mechanics, you can model antimatter interactions as a sort of time-reversal of matter interactions -- leading to the bizarre notion that antimatter is just normal matter that's "backwards" in time. Perhaps entropy provided enough of a "time arrow" to force a bias in the early universe's composition. (Or, as I sometimes muse, there might be some as-yet-unknown force that is responsible for breaking symmetry in time, and entropy as we understand it is just a product of this force.)
The "antimatter is just matter backwards in time" concept was kind of a shocker to me, taking quantum mechanics classes as a college undergrad. I'd been introduced to the concept by a story or novella that was published in Analog, and had dismissed the idea as hokey... and then one day, I cracked open one of my textbooks and saw a weird little diagram, and asked why there was an electron moving backwards in the time dimension, to which the professor responded, "That's a positron."
See Clowe, Douglas et al (2006). "A Direct Empirical Proof of the Existence of Dark Matter," The Astrophysical Journal, ISSN 0004-637X, 648 (September 10): L109-L113.
It was big news at the time so Google will find you plenty of commentary online.
My own instincts suggest that we will eventually come to realise that dark matter and "dark energy" are as close as we will ever get to the main game in town and that baryonic matter will come to be seen as just the scum on the pond.
-- Our systemic servants do not good masters make.
>> Gravity doesn't obey Newton's laws on the very small scale (atomic)...
>
>What gives you that idea?
Quantum Gravity
"the first quantum-mechanical corrections to graviton-graviton scattering and Newton's law of gravitation have been explicitly computed (although they are so astronomically small that we may never be able to measure them)"
That's because you don't know all the details about dark matter.
Here's the quick overview:
On large scales the matter in the universe doesn't seem to behave as it should. We can explain this by hypothesizing extra matter we can't see. Others have attempted to explain it by hypothesizing that gravity doesn't work the way we think it should, AND that there's matter we can't see.
For various reasons it seems very likely that there are a set of very massive particles with certain properties. This is according to one of the most wildly successful theories of all time. It's been used to predict the (later confirmed) existence and properties of several other particles. The properties of these particles are quite like what is needed to explain all that matter we can't see. Moreover, these particles should have been created in the big bang in amounts that are suspiciously like the amount of that unseen matter we need.
So here are the major alternatives. One, dark matter exists and consists mainly of massive, weakly interacting particles. Two, we're wrong about gravity, particle physics and the big bang. Oh, and we still need dark matter anyway.
Look at the bottom of this link. Dark matter and antimatter are two separate issues. Antimatter was verified with the observation of the positron that you mention in the 1930's and the existence of antimatter hasn't really been debated since then. Dark matter is something totally different... it's existence is suggested by astrophysical data and not by experimental particle physics. There is no theoretical understanding of dark matter. It's all suggested by observation. Of course, that's the way science is supposed to work, but in a few cases theoretical understanding preceded observation, as was the case with antimatter.