PDA

View Full Version : Is there a reason we see so many globulars in Sagittarius (toward galaxy's centre)?



AndrewJ
2009-Jul-04, 11:33 PM
I envisage the direction of Sagittarius as being one of the points where our ecliptic intersects the galactic plane. Why are globulars so prevalent in that direction? I had thought globulars inhabited a spherical halo around the galaxy and so would be easier to see when you weren't looking accross the Milky Way and into our galaxy.

ngc3314
2009-Jul-04, 11:46 PM
I envisage the direction of Sagittarius as being one of the points where our ecliptic intersects the galactic plane. Why are globulars so prevalent in that direction? I had thought globulars inhabited a spherical halo around the galaxy and so would be easier to see when you weren't looking accross the Milky Way and into our galaxy.

It's more accurate to think of them as inhabiting a roughly spherical region in which they are concentrated toward the center. Broadly, they follow the radial distribution of the oldest stars, but are much easier to pick out than the individual stars. (This omits such details as the dissolution of looser globulars due to galactic tides, which depends on both their density and orbits).

AndrewJ
2009-Jul-05, 12:07 AM
It's more accurate to think of them as inhabiting a roughly spherical region in which they are concentrated toward the center.

Thanks. So they are more concentrated in the area (within the sphere) that is above and below our galaxy's hub than toward the edge of the sphere?

John Jaksich
2009-Jul-05, 10:44 AM
Thanks. So they are more concentrated in the area (within the sphere) that is above and below our galaxy's hub than toward the edge of the sphere?

The standard answer is yes--and I will attempt to expand upon it---

Globular clusters are termed Population II--and they are sometimes thought of as being formed when the Galaxy, itself was formed. Also, they are termed metal-poor--and are normally found to be spherically distributed about the galactic center--while open clusters (e.g. the Pleiades) are found normally within the disk, itself.

Open clusters are younger and are termed Population I...

Here is an interesting link from the NASA APOD on globulars:

http://apod.nasa.gov/apod/globular_clusters.html

AndrewJ
2009-Jul-06, 02:15 AM
Thanks, folks. Good to get a straightforward answer.