How on Earth This is possible? (distance to a far galaxy)

  • Context: Undergrad 
  • Thread starter Thread starter Prof Sabi
  • Start date Start date
  • Tags Tags
    Earth Galaxy
Click For Summary
SUMMARY

The forum discussion centers on the cosmic alignment of the galaxy ESO 325-G004, located 450 million light years away, which is positioned between us and a more distant galaxy that is currently 17 billion light years away. This alignment demonstrates a critical aspect of Einstein's theory of general relativity, particularly in the context of an expanding universe. Participants clarify that the light from the distant galaxy did not take 17 billion years to reach us; rather, due to the universe's expansion, the distance has increased during the light's journey. This phenomenon highlights the complexities of cosmic distances and the implications for our understanding of time and space.

PREREQUISITES
  • Understanding of Einstein's theory of general relativity
  • Familiarity with concepts of cosmic distance and light travel time
  • Knowledge of the expanding universe model
  • Basic grasp of astronomical measurements and alignment
NEXT STEPS
  • Research the implications of cosmic alignment on gravitational lensing
  • Study the expansion of the universe and its effects on light travel
  • Explore the concept of redshift in relation to distant galaxies
  • Investigate the methods used to measure astronomical distances, such as standard candles
USEFUL FOR

Astronomers, astrophysicists, students of cosmology, and anyone interested in the implications of general relativity and cosmic structures.

Prof Sabi
Messages
33
Reaction score
4
https://amp.scroll.in/article/88372...ivity-holds-true-even-beyond-the-solar-system

Read the Section in this link:
Cosmic alignment
The galaxy we investigated has the catchy name ESO 325-G004 – let’s call it E325. Located some 450m light years away, it is one of the closest examples of a rare cosmic alignment – sitting directly between us and a second, more distant, galaxy. The background galaxy in this case is some 17 billion light years further behind. The centres of these two galaxies are aligned to better than one ten-thousandth of a degree.

17 billion light years? Isn't the universe 13.7 billion years old?
 
Astronomy news on Phys.org
At 17 Gly is where it is now, not at the time when it emitted the light that is captured in the picture.
 
BvU said:
At 17 Gly is where it is now, not at the time when it emitted the light that is captured in the picture.
Need a lil elaboration :eek: ... as I am imagining in this way that the light from that Galaxy literally took 17 billion years to travel to us in with velocity 'c'.
 
Prof Sabi said:
Need a lil elaboration :eek: ... as I am imagining in this way that the light from that Galaxy literally took 17 billion years to travel to us in with velocity 'c'.
Let's say the light is emitted at a distance D from the observer. In a non-expanding universe, that initial distance would remain constant in time, and it'd take t=D/c to cover the distance.
In an expanding universe, as the light travels, the distance D grows - both in the part that the light still has to cover, and the part already covered.
This means that the time needed to reach the observer is higher than t=D/c, and the distance at which the source galaxy ends up being by the time of reception is higher than the initial distance D.

edit: typo
 
Last edited:
  • Like
Likes   Reactions: alantheastronomer, davenn and jim mcnamara

Similar threads

  • · Replies 12 ·
Replies
12
Views
2K
  • · Replies 9 ·
Replies
9
Views
1K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 0 ·
Replies
0
Views
538
  • · Replies 0 ·
Replies
0
Views
2K
  • · Replies 11 ·
Replies
11
Views
3K
  • · Replies 34 ·
2
Replies
34
Views
5K
  • · Replies 12 ·
Replies
12
Views
4K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 23 ·
Replies
23
Views
3K