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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."
TFA brings up a good point, all this dark matter had to have condensed into big star-like masses and should still be around but it wouldn't just be pure dark matter there would be hydrogen and helium too and on the other hand stars like our sun should have dark matter in them too so where is it? if this dark matter is indeed doiung what they say why the heck heven't we detected it in some way?
Sigs are too short to say anything truly profound so read the above post instead.
What makes normal matter collapse is the "friction" or "interaction" between the charged particles. Dark matter is neutral as far as we know and it does not interact through the EM-forces. Hence the name "dark," meaning it does not interact with light either. It is hard to form models where dark matter "collapses". The reason is that the dark matter particles do not exchange energy/momentum easily, as they interact through the "weak" forces only.
As matter clouds condenses, gravitational energy is released. This energy has to be radiated away for the collapse to proceed, as the collapse is opposed by the thermal kinetic energy of the matter in the cloud. This was a major problem in the early universe when the abundance of metals was so low that radiation cooling was less efficient. If dark matter interacts very weakly with normal matter and electromagnetic fields, cooling is going to be very slow indeed. We know that dark matter exists and that it forms concentrations on the scale of large galaxies. We do not have strong evidence for the concentration of dark matter in the solar system, where it could result in apparent radial variations in solar or planetary masses. I supect that cooling of stellar mass dark matter clouds is rather difficult. Once somebody figures out how to observe the stuff and its properties, we can better understand what we see and what we should be looking for.
A sufficiently advanced civilization that doesn't destroy itself first will inevitably optimize their environment to the point of harvesting every last drop of energy from their star(s), such that we can't detect anything but the gravitational effects.
This mysterious "dark matter" structure is termed a Matrioshka Brain (aka: Dyson Sphere).
I understand that this theory's still a bit too shocking for many to seriously consider, so "exotic particles" - or ANY other explaination - it must surely be.
Power to the Peaceful
Does it seem weird to anyone else? Now I haven't stayed up to date with dark matter, but they keep insisting that it MUST be there. It almost seems to be the ether that was claimed to be around us before Einstein blew that one open.
So, hey thanks for posting my submission, man, but enough with the sub-editing, already! Don't I got no artistic rights here? Now we see the violence inherent in the system! Don't give me any of that intelligent life crap... this is Slashdot. Just give me something I can troll. Help! Help! I'm being oppressed!!!
E_TOO_MUCH_PYTHON
Everything I needed to know about life, I learnt from Blake's Seven
The purpose of dark matter is not just to explain spiral galaxy rotational curves. The bigger problem is the energy budget of the universe.
If you ONLY read the NASA press releases with colorized images, that is, I am afraid your problem. There is over-whelming evidence for the existance of dark matter and what are scientists to do if the only thing that puts dark matter on a \.er's mind is just a pretty picture. If you are interested, go to arxiv.org and search for results from dark matter experiments and read the papers. Yes, they are technical. Yes, it produced many PhDs -- not a bad thing, last time I checked. And yes, the experimental evidence is overwhelming.
The number of people working on dark matter experiments, greatly exceeds the number of dark matter theorists, probably by an order of magnitude actually. This is *the* one field in astro-particle physics, where there is great wealth of data and that data is driving the evolution of the field. In particle physics, this is not the case! There is no data on particles which might form dark matter! There are too many theories! Hopefully, the tables will turn when the LHC at CERN turns on next year!
I should also point out that this is one of the "nicest" sort of theoretical astrophysics papers there is. It suggests a possible phenomena that produces an experimental signature in space experiments like or AMS.
I'm not 100% sure that this is what you're getting at, but for the less physically inclined (including myself) let me try an alternate explanation - please feel free to shoot holes in it.
Ok, you're a hydrogen atom floating in DEEP space. You feel the tug of a galactic cluster, so you start moving towards it. Then you feel the tug of a galaxy, so you start moving towards it. Then you feel the tug of a random planet like the Earth, so you start moving towards it. All along you have been bumping into other hydrogen atoms, so by the time you get to the earth you are moving fast, but not insanely fast. You hit the earth and get stuck in the dirt.
Now, picture that you're a particle of dark matter, whatever that is, with a little bit of apparent mass. You start out in DEEP space and happen to fall all the way to the Earth. But, this time you haven't interacted with anything along the way, and so you're still flying along at 99% of the speed of light. You fly through the Earth, out of the galaxy, out of the cluster, and start slowing down until you fall back towards the cluster. So, you're essentially orbiting on a galactic scale or larger.
So, at any given time there might be dark matter particles within the boundary of the Earth, but they're only transiently present. They don't accumulate on the Earth because most are just orbiting on a galactic scale. That's why you don't see them.
In order to stay around the Earth objects need to have a similar velocity. Not many particles of dark matter would be likely to have a similar velocity to the Earth, because there isn't any real way for them to clump up - except as just big balls of gas on the galactic scale.
Is this a decent explanation?
Although I'm not an astrophysicist, I have studied astrophysics as an undergraduate and know some things about dark matter theories and cosmology. You are absolutely correct in saying that dark matter must be non-baryonic under current models. Baryonic dark matter is excluded because big-bang nucleosynthesis models (which take observed primordial elemental abundances as input) show that only ~4% of the mass of the universe can be baryonic matter.
You are, however, incorrect in stating that dark matter shares no properties with ordinary matter besides gravity. All energy, including electromagnetic radiation and dark energy, affect the curvature of spacetime. Dark matter also has the property that it behaves in the same way as matter when the universe expands, i.e. that its density decreases as the cube of the scale factor (which determines the rate of expansion). Ordinary radiation and dark energy each behave differently in this regard, so dark matter is indeed uniquely matter-like in a very important way. Aside from galactic rotation curves, very good data from the WMAP project that studies the cosmic microwave background has determined that ~30% of the universe must be matter-like. Combined with the BBN studies, this means that 26% of the universe, by mass, is dark matter, which thus outnumbers ordinary matter by more than a factor of 6.
You are also incorrect in assuming that we haven't found dark matter. There is actually a very excellent photo of colliding galaxies that shows convincing evidence of dark matter. The caption does a decent job at giving an explanation of the photo's significance. If you want a more thorough explanation, both of the photo and why the result is significant, I recommend this blog maintained by several well-known cosmologists.
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