speising wrote:are the stars at the center junger than the ones at the rim?
Indeed they are! Halo stars are much older, and have much lower metallicities on average, than disk stars, which is confusing if you assume we started out as a big cloud of hydrogen; you'd expect older stars to have had more time to fuse hydrogen into heavier elements.
drachefly wrote:The distribution of dark matter is roughly spherical around galaxies. This would produce a flat disk if it produced any gravitationally bound structures at all.
You've hit the nail on the head! The flat disk it produces is the disk of visible matter in our milky way; the dark matter isn't necessary.
Tyndmyr wrote: Are you implying that redshift is generally not a result of movement away, and simply indicates mass?
No, I'm applying the equivalence principle, in which a gravitational potential well is identical to an accelerating reference frame:
You can still have doppler blueshift, and indeed we see it in spiral arms that are receding from us, but you can also have gravitational redshift. That way, the additional redshift of structures much further from us in the universe (i.e. further back in time) don't present the geometric nastiness of a universe where everything is accelerating away from a central point that appears to be our galaxy.
gmalivuk wrote:Yeah, it definitely doesn't avoid the need for dark matter, because it doesn't explain galactic rotation curves
Droplets flung from a sprinkler have very little angular momentum, right? They only look like they're spinning because of the emission pattern? They're not strictly radial, but they move in a straight line away from a point very close to the axis of the sprinkler?
So it seems like the theory doesn't explain:
- Non-spiral galaxies;
- Galactic rotation rates;
- The CMBR data showing mostly non-baryonic mass; or
- Gravitational lensing in dark places.
I don't know how to explain to you the way in which it explains galactic rotation rates besides to say that matter is flung out tangentially rather than radially, and the radial component of its momentum is depleted by gravitational pull from the mass remaining at the center. You can't approximate even the black holes as point particles.
Fortunately for you two and Laserguy, the nice folks at NASA once did a simulation of something which I'd consider close enough for government work.http://www.space.com/25863-neutron-star ... video.html
Hopefully you can see now how, starting from much denser initial objects, you might end up with a nice milky spiral. If not, hopefully you at least enjoyed the cool video.
To address your question of non-spiral galaxies...have you noticed that they're few and far between, and tend to contain stars much older than those found in spirals? They're also much less common in the early universe; this is consistent with Laserguy's postulation that they might be the result of mergers, and also with the idea that older galaxies tend to spread out into more diffuse clouds once they've lost their massive, active cores. Ellipticals tend to be unusually quiet with regards to star-formation, which is consistent with the diffusion model but not so much the "merger" idea.
Meteoric wrote:If black holes have a maximum angular velocity, does it work to posit that primordial black holes were born exceeding it?
It depends! There's a lot of room for interpretation--the maximum angular momentum is determined by M, G and C, so if you'll permit a universe where those are changing, you might have a model where primordial black holes exceed their maximum angular momentum because the gravitational force binding them is growing weaker. This might violate the equivalence principle, though, as a decrease in gravitational energy would lead to a corresponding decrease in momentum. If you want to flux with the values of C, you might be able to skirt that, but I'm far enough out on a limb here as is, for now.
If you prefer static constants (as I do), then the maximum angular momentum is exceeded when two bodies meet. While each was stable before, the system of the two exceeds Lmax
, as in the Neutron Star Collision video, above. This was my original hypothesis, but I haven't been watching long enough to tell you you're wrong if you can find some evidence that supports a falling G or something.
To address Copper Bezel and Gma's comments regarding calling the particles "Hawking Radiation"--you're absolutely right. It wouldn't be proper to call it that. The phenomenon wouldn't have a known name, as it's a new amalgamation of a number of already-existing concepts. I bring up Hawking radiation and the Penrose Process merely to illustrate that currently-accepted mathematics allow for the creation of massive and charged particles in regions of space with extreme energy density gradients, such as those one might find near the ergosurfaces of orbiting PBHs. We know that galactic nuclei are tremendously active, spitting out gamma rays of tremendous energy (with a peak at 511 keV...interestingly enough), so it doesn't seem unreasonable to me to assume that baryons could be forged there, too.
AFAIK, we haven't probed the region, but this would tell us to expect a 938 MeV line as well, so if you're an astro grad student looking for a thesis, get to it and dibs on Corresponding Author status if you find it.
Have a paper by some legitimate astrophysicists contradicting standard dark matter models, in case you still feel like current theory has fewer holes in it than this one: http://www.space.com/15499-dark-matter- ... tures.html
With regards to the Illustris simulation; it would allow for the formation and interaction of black holes, wouldn't it? It's not immediately apparent from the images how those spiral structures emerge in the simulation--perhaps it's by this method.
Hypnosifl wrote:it's entirely consistent with the basic framework of quantum field theory to postulate undiscovered massive particles that interact only via the weak force and gravity (as some known particles like neutrinos do).
The whole point of this exercise is that, occam's razor-wise, it's inelegant to postulate these particles unless you've exhausted all means of explaining our observations through known mechanisa. I cannot explain your magic bullet at present, but I would question my own imaginative capacity before I started attributing its motion to particles which defy all known mechanics.