In an answer to another question, a claim has been made that orbit/spin orientations are random (at least within our own Galaxy), except perhaps towards the Galactic centre.

I have dabbled in this area before ( http://adsabs.harvard.edu/abs/2010MNRAS.402.1380J ) and there is a recent paper by Rees & Zijlstra (2013) that suggests planetary nebulae in the Galactic bulge with bipolar morphologies have an alignment with the Galactic plane at 3.7 sigma significance. The hypothesis is that this is due to an alignment of the orbital axes of their parent binary systems, such that the orbital planes of the binary systems are perpendicular to the Galactic plane.

My question: Is there any other evidence for such alignments in other classes of source in the bulge or elsewhere in the Galaxy? Or are there any studies that comprehensively show that angular momentum vectors (spin or orbital) are randomly aligned?

  • $\begingroup$ I've read articles about orientations of stars in globular clusters. It's random. The orientations of recently discovered planetary systems is also apparently random. I'll try to dig up references later. On the other hand, there are signs that rotations near the galactic core are correlated (as you have read). $\endgroup$ – David Hammen Nov 23 '14 at 2:21
  • $\begingroup$ See also This Answer $\endgroup$ – JDługosz Sep 8 '15 at 9:09

In general the planes of solar systems are not aligned with the plane of the Galaxy, but are oriented in all different directions. The size of a solar system is so much smaller than the size of the Galaxy, that the Galaxy's structure has no impact on the orientation of a solar system. What determines their orientations is the direction of the angular momentum that the system had when it formed, and that's pretty much random. For instance, our own solar system is tipped by about 63 degrees with respect to the plane of the galaxy.

Recent numerical simulations of the star formation process (Bate, Bonnell & Bromm , (2002) MNRAS, 332, 705 & (2003) MNRAS, 339, 577; Bate M. R., (2009), MNRAS, 392, 590 & (2009) MNRAS, 392, 1383) have considered the formation of stars within clusters, starting with initial turbulent conditions for the gas which are designed to mimic those seen within star-forming molecular clouds. The picture which results involves turbulent and chaotic motions of both gas and stars, with disc fragmentation, competitive accretion and close dynamical interactions all playing a role.

In addition, Bate, Lodato and Pringle, Mon. Not. R. Astron. Soc. 401, 1505–1513 (2010), found that the final stellar rotation axis and disc spin axis can be strongly misaligned, which may lead to planetary systems with orbits that are misaligned with the stellar rotation axis

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    $\begingroup$ Thanks, I appreciate the contribution, and you may end up with some bounty, but you can't answer this question by making assertions. How is it known that solar systems (other than our own) are not aligned with the Galactic plane? Has someone done a proper statistical study of projected orbital planes - the transit systems may be oddballs. The numerical simulations (not observations) of Bate et al. do not take place in a Galactic potential and don't include magnetic fields, both of which could conceivably align angular momentum vectors of giant molecular clouds. $\endgroup$ – ProfRob Dec 1 '14 at 20:37
  • $\begingroup$ "Star rotation axis can be misaligned with disk rotation axis". Wow, it is going to take a while for this to sink in. $\endgroup$ – John Alexiou Dec 1 '14 at 21:07
  • $\begingroup$ @ja72 Don't get too excited. This is also a theoretical simulation. Observations of disks and rotation might suggest otherwise - adsabs.harvard.edu/abs/2011MNRAS.413L..71W $\endgroup$ – ProfRob Dec 1 '14 at 21:42
  • $\begingroup$ @RobJeffries I am gonna try to find some experimental stuff, but my guess is that it is not much out there, otherwise at least these theoretical papers would have to mention it, either in the introduction or in the discussion. $\endgroup$ – Wolphram jonny Dec 2 '14 at 4:27

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