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View Full Version : Velocity of SgrA* Relative to Our Solar System



Dave Zelenka
2007-Jan-09, 07:10 PM
I'm looking for the velocity of SgrA* (the center of our galaxy) relative to our solar system.

antoniseb
2007-Jan-09, 07:22 PM
How are you looking?
Are you looking at the redshift from ??? Arcs that seem to have started at Sgr A*? You can't really get a redshift from the object itself.

Dave Zelenka
2007-Jan-09, 08:06 PM
I didn't think that stars in our local galaxy could be determine by redshift. So there might not be a way to get the relative motion of Sgr A*. It may be too distant. I'm just trying to find out if there is observational data that will determine our solar system's relative motion in the galaxy. I'm not looking for its theoretical motion.

Amber Robot
2007-Jan-09, 08:23 PM
I'm just trying to find out if there is observational data that will determine our solar system's relative motion in the galaxy.

Look up "local standard of rest".

Nereid
2007-Jan-09, 09:26 PM
Here are some resources: SEDS (http://www.seds.org/messier/more/mw.html), dovada (http://www.dovada.com/orbital_data.htm) (perhaps a bit too simplified?), NRAO (http://www.nrao.edu/pr/1999/sagastar/), estimated motion over last 500 million years (http://www.journals.uchicago.edu/cgi-bin/resolve?id=doi:10.1086/430250&erFrom=7137904341753796488Guest).

You might want to Google on LSR (local standard of rest (http://scienceworld.wolfram.com/astronomy/LocalStandardofRest.html)), to get a handle on the difference between the solar system barycentre's motion and that of a hypothetical star in a perfectly circular orbit.

LEDA's vgsr (http://leda.univ-lyon1.fr/leda/param/vgsr.html) may help too.

While the data in these are not completely consistent, I think they give you a pretty accurate set of estimates.

Dave Zelenka
2007-Jan-09, 10:15 PM
Thanks for the links. It sounds like the relative motion to the center of the galaxy is unknown. The angular motion has been estimated, but not whether or not it is moving in our out...or at least from what I could find. Could this be because this velocity is so slight?

Dave Zelenka
2007-Jan-09, 10:21 PM
I did find an estimate of the Sun's U velocity, which was stated to be moving toward the center of the galaxy, but I have been unable to find how that was determined, observationally or through theoretically.

Nereid
2007-Jan-10, 03:36 PM
The simplest answer is: the solar system barycentre is moving wrt a hypothetical object in a circular orbit around SgrA*, with radius the same as the distance of that barycentre to SgrA*, with a velocity described in the LSR links.

The velocity of "object in a circular orbit around SgrA*, with radius the same as the distance of that barycentre to SgrA*" is completely determined by knowing the period (and the distance).

The distance has been reliably determined by a variety of means; the period perhaps not so strongly constrained (but for an estimate of the velocity, uncertainty in the period contributes but a small error) - details are in at least some of the links above (or references contained in those links).

The motion of the barycentre wrt the LSR has been most tightly constrained by the HIPPARCOS mission (http://www.rssd.esa.int/Hipparcos/).