Mass of a galaxy without dark matter and with dark matter

  • Thread starter Quarlep
  • Start date
  • #1
257
4

Main Question or Discussion Point

I am curious about mass of a galaxy without dark matter and with dark matter.I searched but I couldnt found.I ll be happy If you help me.

Thanks
 

Answers and Replies

  • #2
phinds
Science Advisor
Insights Author
Gold Member
2019 Award
16,240
6,322
Well, without dark matter there most likely would not BE any galaxy. although DM does not "clump" the way normal matter does, it has somehow accumulated into cosmologically massive blobs that then attract regular matter through gravitational attraction and the regular matter clumps into stars and planets and dust and the whole mess is a galaxy.

So asking what a galaxy would be like without the dark matter is a bit like asking how well someone could sing if they had no vocal chords.
 
  • #3
257
4
Without dark matter I mean without dark matter mass my fault I forget mass
 
  • #4
phinds
Science Advisor
Insights Author
Gold Member
2019 Award
16,240
6,322
Without dark matter I mean without dark matter mass my fault I forget mass
Yes, that is exactly what I was talking about.
 
  • #5
34,489
10,617
Without dark matter I mean without dark matter mass my fault I forget mass
How does that change the question?

For an existing galaxy, you can ask how much visible and how much invisible mass there are. The answer depends on the galaxy and the radius you consider (galaxies do not have sharp edges, especially in the dark matter distribution), but there are many galaxies where numbers are available online.
 
  • #6
wabbit
Gold Member
1,284
207
I think the ratio of dark matter to matter is about the same in a typical galaxy (DM halo included) as the overall ratio of 85:15 but I could very well be wrong.
 
  • #7
phinds
Science Advisor
Insights Author
Gold Member
2019 Award
16,240
6,322
I think the ratio of dark matter to matter is about the same in a typical galaxy (DM halo included) as the overall ratio of 85:15 but I could very well be wrong.
The rabbit ? WRONG ? Not very likely :smile:
 
  • #8
wabbit
Gold Member
1,284
207
Don't joke about the poor rabbit :) he's still recovering from almost loosing his legs in a black hole:smile:
 
  • #9
257
4
Is that right isnt it 85/15
 
  • #10
Vanadium 50
Staff Emeritus
Science Advisor
Education Advisor
2019 Award
24,801
7,812
I think the ratio of dark matter to matter is about the same in a typical galaxy
There exist both DM-rich and DM-poor galaxies.
 
  • #11
phinds
Science Advisor
Insights Author
Gold Member
2019 Award
16,240
6,322
Is that right isnt it 85/15
do you not understand that 85:15 IS 85/15 or are you making a joke?
 
  • #12
phinds
Science Advisor
Insights Author
Gold Member
2019 Award
16,240
6,322
Don't joke about the poor rabbit :) he's still recovering from almost loosing his legs in a black hole:smile:
I TOLD you to stay away from those things !
 
  • #13
wabbit
Gold Member
1,284
207
Yes mom, I won't do it again, promise:)
 
  • #14
wabbit
Gold Member
1,284
207
There exist both DM-rich and DM-poor galaxies.
I was wondering about that, or something related rather - in galaxy collisions the matter tends to coalesce into a single galaxy after a while due I believe to some kind of friction - but with high enough collision velocity it seems that (some part of) the dark matter halos could just move through each other and continue on their way. If that does happen, not only would we be left with a DM poor merged galaxy, but also with stray haloes of dark matter zooming away without much matter left in them . Is that something that happens and if so do we see such stray halos (through lensing or other means)?
 
  • Like
Likes Kelson Adams
  • #15
34,489
10,617
Well, there are objects like the bullet cluster where the distribution of dark matter differs significantly from the distribution of gas.
Stars also don't have much friction, so a complete separation of visible and dark matter would be odd.
 
  • #16
wabbit
Gold Member
1,284
207
Thanks, I thought "some kind of friction" arising from matter-matter interaction (gas clouds maybe?) played a role in the merger process - but you re saying it's minor and essentially gravitational effects alone explain the process, did I get that right?

And yes I was thinking of the bullet cluster - though I don't recall seeing mention of stray halos escaping in that case, so I was freely extrapolating - perhaps a little too far : )
 
  • #17
phinds
Science Advisor
Insights Author
Gold Member
2019 Award
16,240
6,322
Thanks, I thought "some kind of friction" arising from matter-matter interaction (gas clouds maybe?) played a role in the merger process - but you re saying it's minor and essentially gravitational effects alone explain the process, did I get that right?
Actually, I think the dust interactions DO contribute an effect, it's just that stars/planets are so far apart that THEY don't hit each other.
 
  • #18
257
4
do you not understand that 85:15 IS 85/15 or are you making a joke?
Yeah I understand it like that
Its not 85/15 then what it is.
 
  • #19
257
4
I was watching House and there House said dark matter makes galaxies 6 times bigger mass.And I am curious about is that same for every galaxy ? Example a galaxy mass is m without dark matter.But with dark matter 6m.Is that true for all galaxies ? (85/15 near to 6 so I made a connection)
 
  • #20
phinds
Science Advisor
Insights Author
Gold Member
2019 Award
16,240
6,322
I was watching House and there House said dark matter makes galaxies 6 times bigger mass.And I am curious about is that same for every galaxy ? Example a galaxy mass is m without dark matter.But with dark matter 6m.Is that true for all galaxies ? (85/15 near to 6 so I made a connection)
Which part of post #10 did you not understand?
 
  • #21
257
4
There exist both DM-rich and DM-poor galaxies.
So DM does not depend mass of galaxy.But this sound like stupid I guess.In quote I guess he means mass depend DM which less mass galaxies have Poor DM and heavier galaxies have Rich Dm
 
  • #22
Chronos
Science Advisor
Gold Member
11,408
738
The whole DM issue is confusing. Some galaxies appear to be rich in it, and others largely lacking. That suggests we may be missing an important clue.
 
  • #23
257
4
I understand.Do you have any internet resources for that.This extra mass idea or DM rich DM poor stuff
 
  • #25
Vanadium 50
Staff Emeritus
Science Advisor
Education Advisor
2019 Award
24,801
7,812
But this sound like stupid I guess
If you don't like what I said, provide a counterexample or counterargument, or at least ask a question. Don't just call it stupid. It's not just unhelpful. It's rude.

If you bothered to type "dark matter rich galaxies" in Google, you would have gotten 70,600 hits. If I were you, I'd do a bit more research before telling other people that they are wrong.
 

Related Threads on Mass of a galaxy without dark matter and with dark matter

Replies
1
Views
2K
Replies
1
Views
3K
Replies
5
Views
13K
Replies
5
Views
2K
  • Last Post
Replies
14
Views
2K
Replies
3
Views
3K
Replies
8
Views
3K
Replies
14
Views
1K
Replies
4
Views
3K
  • Last Post
Replies
15
Views
2K
Top