Inclinations of star orbits in the Milky Way

[VladZH]

Do all stars orbit around the black hole in the same plane? Or some stars can have the same orbital radius but slightly different orbital inclinations?

 

[jim mcnamara]

It is more complex than that: https://en.wikipedia.org/wiki/Spiral_galaxy#Galactic_spheroid
The galactic spheroid is a ball-shaped halo of stars that extends in all directions, not just the galactic plane. This is a LARGE number of stars out there.

In terms of the galactic core: https://en.wikipedia.org/wiki/Sagittarius_A*
The black hole is part of a small clusters of smaller stars with orbits thought to be in many different highly elliptical orbits due to the BH there.

Hypervelocity stars are 'rogue' stars with very high velocities relative to all their neighboring stars.
https://www.space.com/19748-hypervelocity-stars-milky-way.html

There was a paper published lately about the origin of some of these hypervelocity stars: the Lesser Magellanic Cloud - smallish galaxy that orbits the Milky Way. Preprint only so far:
https://arxiv.org/abs/1704.01373

Kind of cool!

 

[VladZH]

Thanks for reply. What I figured out about spiral galaxies:
1) The stars in a disc incline slightly
2) There is a center bulge where stars can have any inclinations
3) And a galaxy has a halo where stars are gathered in globular clusters orbiting a galactic center
Are there stars just following a galaxy, not orbiting a center?

 

[jim mcnamara]

Are there stars just following a galaxy, not orbiting a center?

I do not know. It appears to me: Hypervelocity stars can have trajectories or orbits unrelated to the center of mass of a galaxy. Per the last paper cited above.

 

[newjerseyrunner]

Even a star that is more or less in the plane, does not orbit in a flat circle. Stars bob up and down through the galactic plane, sort of like this: