Expert: James Gort - 4/27/2010

Question
i am not sure if this has any significance or not but i imagine it might. as we look in on the sun the earth and all the planets from our perspective rotate left to right and i,m wondering if the many exo planets that have been discovered are rotating their stars in the same way and likewise galactic rotation if the universe was rotationally polarized i imagine that would tell us something very interesting .
                        is this too simplistic a question if so no reply needed and no offence taken.
                      thank you.
                        kieran.

Answer
Hi Kieran,

This is definitely not a simplistic question.  In fact, it's probably one of the most thought-provoking questions I've received, and one which is the subject of considerable research.

Within our solar system, the answer is easy.  Because the original dust and gas cloud which condensed to form the sun and the planets had some angular momentum, the conservation of angular momentum dictates that the condensing bodies will retain that momentum.  The question is:  why did the dust cloud have a preferred direction?  Was it because the Milky Way galaxy is rotating, and imparts that angular momentum to all its dust and gas?  Does that mean exo-planets will be rotating in the same general direction?  What about other galaxies (and its assumed exo-planets)?  

Because this is a topic of some research and debate, I'm going to do a little research myself and find the best answer for you (and for myself).  I will get back shortly, and hopefully, can give you the latest findings.

Thanks for a truly great question.

UPDATE:

As I suspected, there's little consensus.  The stars near our sun seem to preferentially rotate in the same direction (as determined primarily from multiple stars - data on exo-planets is a little sketchy, but seems to support this also).  As our galaxy rotates, there is a differential velocity of galactic matter as it orbits the galactic center.  That differential velocity causes most large gas/dust clouds to have some inherent rotation.  As the cloud condenses to form a star and planets, it retains that rotation (through the conservation of angular momentum).

Why does the Galaxy rotate?  Do nearby galaxies seem to preferentially rotate in the same direction?  The answer to the latter is "no".  And with that answer, we can answer the first question with "we don't know".   Was it due to random motions which were not quite random?  Perhaps.  Cosmologists are still studying that!

Your observations were very astute.  Unfortunately, we don't have all the answers!
   

Prof. James Gort