Undergrad Inquiry Regarding the Determination of the Galactic Disk's Outer Bound

[MountKobau]

I have recently read research papers that mention that disk stars have been found up to distances as far as 25 kpc from the milky way galactic center and possibly even up to distances as far as 31 kpc. I was wondering if there is a particular distance (or distance range) observed where the galactic disk ends/reaches its edge and no disk stars are being observed and measured at? Or is it possible that the exponential disk continues (albeit at very low densities) to very large distances (> 200 kpc)?

My next question is a follow up to the first, Is there a upper limit to the size the galactic disk of the milky way can theoretically attain (in terms of R in kpc)? Or is possible for the disk to go on indefinitely (but just very hard to detect at very large distances due to low density, lack of data and powerful enough telescopes)? If there is a limit, what would be the limiting factors?

 

[phinds]

Is there a upper limit to the size the galactic disk of the milky way can theoretically attain

The Milky way is approximately 100,000 light years across and I'm not aware of any reason that it will change size in the next many trillions of years, probably longer.

I have no idea how far out disk stars have been seen, or are likely to be, but I can't think of any reason why they could not exist pretty much out to the edge (which is 15kparsecs from the center so NOT consistent with the findings you "quote" which imply a much greater size for the galaxy than is correct).

Also, just FYI "I have recently read research papers" is NOT considered an acceptable citation here. Be specific.

 

[MountKobau]

The Milky way is approximately 100,000 light years across and I'm not aware of any reason that it will change size in the next many trillions of years, probably longer.

I have no idea how far out disk stars have been seen, or are likely to be, but I can't think of any reason why they could not exist pretty much out to the edge (which is 15kparsecs from the center so NOT consistent with the findings you "quote" which imply a much greater size for the galaxy than is correct).

Also, just FYI "I have recently read research papers" is NOT considered an acceptable citation here. Be specific.

Link to the paper mentioned: https://www.aanda.org/articles/aa/full_html/2018/04/aa32880-18/aa32880-18.html

If the diameter of the disk really is 100,000 light years across - which I don't think has been proven by direct observations (if it has please share these observations) - it will definitely change when the MW collides with M31 in 4.5 billions years.

 

[Vanadium 50]

it will definitely change when the MW collides with M31 in 4.5 billions years.

How is that relevant to measurements today?

 

[Vanadium 50]

Let's please stick with light years or parsecs and not mix them.

Ballpark, the MW radius is 15 kpc. This is not a sharp boundary - how could there be? That stars are seen at 2R does not surprise me. They could be just on the tails of the distribution, or stars whose orbits have been disrupted by gravitational interactions with nearby stars.

 

[MountKobau]

How is that relevant to measurements today?

Thanks for the response, it is not relevant to the measurement today, I was responding to the comment saying the measurement won't change for "next many trillions of years".

 

[snorkack]

How do we define the edge of Solar System disc for comparison?

When you are looking at objects present in the outskirts of either, you can classify them by type of orbit:

1. Low inclination, low eccentricity
2. Low inclination, high eccentricity
3. High inclination, high eccentricity
4. High inclination, low eccentricity
5. Unbound, first outbound leg
6. Unbound, inbound leg or second leg

So where does "disc" end? Is it where 1) drops off to the random expected amount compared to 4), or where 1+2) combined match the statistical expected fraction from 3+4)?