Viewing size of Galaxies 7 Billion light years away?

Click For Summary

Discussion Overview

The discussion revolves around the perceived angular size of galaxies located 7 billion light-years away, particularly in the context of the expansion of the universe. Participants explore how this expansion might influence the angular size observed from Earth, incorporating mathematical reasoning and concepts related to redshift.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant initially proposes that a galaxy 7 billion light-years away would appear twice the expected angular size due to the universe's expansion, based on their mathematical calculations.
  • Another participant challenges this view, stating that while the distance between galaxies is expanding, the galaxies themselves are not, suggesting that the perceived size is determined by their actual size and distance.
  • A subsequent post corrects the initial claim, acknowledging a miscalculation and clarifying that the question pertains to how the universe's expansion affects the perceived angular size of the galaxy.
  • Another participant suggests that the expansion of space within galaxies may not result in a noticeable difference in angular size for distant galaxies.
  • One participant introduces the concept of the 'turn over' in the angular size versus redshift relation, providing specific examples of how apparent angular size changes with redshift, including calculations for different distances.
  • A later reply comments on the nature of scientific discourse, contrasting the clarity of scientific facts with political manipulation.

Areas of Agreement / Disagreement

Participants express differing views on how the expansion of the universe affects the perceived angular size of galaxies. There is no consensus on the implications of this expansion, and multiple competing perspectives remain throughout the discussion.

Contextual Notes

Participants reference mathematical calculations and concepts such as redshift without fully resolving the implications of these calculations or the assumptions involved in their reasoning.

Remo Aviron
Messages
3
Reaction score
0
Would a galaxy 7 billion LY away appear to be twice the expected size (angular size) as a consequence of the expansion of the universe? (Assuming the universe is 14 Billion years old). My math says yes. But of course, I am just using trig and geometry. Just curious.
 
Astronomy news on Phys.org
I'm not sure how you are using that math, but the galaxy isn't expanding, just the distance between it and here. It would appear a size dictated by the actual size and distance to it.
 
Update and correction

Sorry, I messed up the math. It wouldn't be double. I know the Galaxies are not expanding. But the Universe is. Space is.

The question is how does the expansion of universe affect the preceived angular size of the galaxy? For example, if the galaxy were 100,000 ly across, you would expect it to occupy an angle of 0.0008 degrees. Does it occupy this angle, a smaller angle or a larger angle.
 
The space between galaxies expands so does the space within a galaxy, so probably you will not see the difference in angular size of that distance galaxy.
 
I think Remo Aviron is talking about the 'turn over' in the angular size vs redshift relation which occurs at about a redshift of ~1.65. If he/she is, then if we consider a standard ruler which has physical size 1kpc at a comoving distance of 1Mpc (0.003 billion LY), it will have an apparent angular size = 200 arcsecond. Moving this object to 7 billion LY (redshift =0.6), it will have apparent angular size = 0.15 arcsec, but moving it to reshift 6 (27.468 billion LY) it will actually have a larger apparent angular size when compared to the object at 7 billion LY, ie. apparent angular size = 0.17.

See http://www.atlasoftheuniverse.com/redshift.html" link for more information.
 
Last edited by a moderator:
Well done, matt, I had a less delicate reply in mind. Scientists excel at discerning facts, politicians excel at manipulating them.
 

Similar threads

  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 12 ·
Replies
12
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 18 ·
Replies
18
Views
12K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 0 ·
Replies
0
Views
1K
  • · Replies 4 ·
Replies
4
Views
2K