Slashdot Mirror
Galactic Pancake Mystery Solved
mOoZik writes "According to the BBC, Astronomers have figured out why a series of small galaxies surrounding the Milky Way are distributed around it in the shape of a pancake. Theorists believed that the eleven dwarf galaxy companions should have a diffuse, spherical arrangement, but a University of Durham team used a supercomputer to show how the galaxies could take the pancake form without challenging cosmological theory."
... and more credit ... (and to enhance discussion :) ...
Full article
The Distribution of Satellite Galaxies: The Great Pancake
Noam I Libeskind, Carlos S Frenk, Shaun Cole, John C Helly, Adrian Jenkins, Julio F Navarro and Chris Power
ABSTRACT
The 11 known satellite galaxies within 250 kpc of the Milky Way lie close to a great circle on the sky. We use high resolution N-body simulations of galactic dark matter halos to test if this remarkable property can be understood within the context of the cold dark matter cosmology. We construct halo merger trees from the simulations and use a semianalytic model to follow the formation of satellite galaxies. We find that in all 6 of our simulations, the 11 brightest satellites are indeed distributed along thin, disk-like structures analogous to that traced by the Milky Way's satellites. This is in sharp contrast to the overall distributions of dark matter in the halo and of subhalos within it which, although triaxial, are not highly aspherical. We find that the spatial distribution of satellites is significantly different from that of the most massive subhalos but is similar to that of the subset of subhalos that had the most massive progenitors at earlier times. The elongated disk-like structure delineated by the satellites has its long axis aligned with the major axis of the dark matter halo. We interpret our results as reflecting the preferential infall of satellites along the spines of a few filaments of the cosmic web.
CC.
TaijiQuan (Huang, 5 loosenings)
Well, maybe *you've* never heard of the University of Durham, but it's one of the foremost universities in the UK, and the Physics group there is extremely well-respected.
This isn't "some kids doing a group project", this is proper academic research; you may have heard of that...
It's official. Most of you are morons.
Even if you have a bunch of uniformly randomly-oriented orbits, there is always at least a little angular momentum in some direction; you never get perfect statistical cancellation to zero. This angular momentum is conserved, and as the cloud of matter collapses gravitationally, the rotational effect is amplified (like a spinning figure skater pulling in his/her arms).
So each galaxy should have non-zero angular momentum. This doesn't mean that there shouldn't be ANY spherical-like orbits, just that the majority of objects orbit in the "pancake" that is perpendicular to the axis of rotation. Here's the punchline: over billions of years, the objects that are NOT orbiting in the galaxy's pancake have close encounters with the more numerous objects in the pancake, and are either flung out of the galaxy or put into more normal orbits. The same process accounts for the fact that all planets in the Solar System orbit in a common plane (called the ecliptic plane).
As for elliptic galaxies, my impression was that they are the result of low-speed collisions between two spiral galaxies of roughly the same size. The two pancakes then combine to form a diffuse cloud of strars. For instance, when the Milky Way impacts Andromeda in 2 billion years (or is it 3? I can't remember), the result should be an elliptic galaxy if I understand the dynamics correctly.
Isn't it supposed to be about challenging current theories?
No, it's supposed to be about parsimony. If you find an explanation of a phenomena that fits with current theories, that's favorable to throwing out a bunch of current theories just to explain your phenomena.
It's called "simpler." We like simpler.