Light Speed & Expanding Galaxies: A Cosmological Mystery

AI Thread Summary
Galaxies can appear to move away from us faster than the speed of light due to the expansion of the universe, but this does not mean they are disappearing from view. Light from some galaxies may still reach us even if they are receding at superluminal speeds, as the expansion of space affects the distance between galaxies rather than their intrinsic speed. While certain galaxies may become unobservable as their light is redshifted beyond detection, they do not vanish suddenly; instead, they fade gradually. Within galactic clusters, galaxies are not affected by this expansion and can even collide with one another. Ultimately, the expansion of the universe creates vast distances that can render some galaxies permanently unobservable.
binbots
Messages
170
Reaction score
3
If galaxies aer expanding fast than the speed of light how are we able to see them. At the moment this expansion surpassed the speed of light shouldn't these galaxies dissappear or remain unchanged visually?
 
Astronomy news on Phys.org
Galaxies are not expanding.

Do you mean moving away from us due to the expansion of the universe? You can see galaxies that appear to be moving away from us faster than the speed of light for much the same reason you can hear an object moving away from you faster than the speed of sound. The speed of light is not dependent on the speed of the moving galaxy.

There is a limit, though, based on the universe expanding so fast the distance is increasing faster than the light moves.
 
binbots said:
If galaxies aer expanding fast than the speed of light how are we able to see them. At the moment this expansion surpassed the speed of light shouldn't these galaxies disappear or remain unchanged visually?

Certain galaxies might be presently unobservable because they are receding from us at faster than light speed due to cosmological expansion. But the light of others might still be streaming on its way toward us and so we see them as they were prior to reaching that superluminal velocity. Keep in mind that the galaxies themselves cannot exceed the 186,000 speed limit. It's the space between galactic clusters that is expanding at that velocity and beyond and thus creating insurmountable distances between us and them and making their present light forever undetectable for us.

Also, we are talking about areas of space where gravity doesn't cancel out cosmological expansion.
Galactic clusters containing from as few dozen to millions of galaxies are not internally affected by that expansion. In fact, within these clusters, galaxies collide and merge. Some. like our Magellanic clouds which orbit our Milky Way are satellites of other galaxies. Andromeda, the largest member of our own galactic cluster is presently approaching us and seems destined to collide with our our galaxy in the far future. The the distancing is between super clusters of galaxies where gravity cannot predominate.

BTW
By unobservable I mean that the light being emitted by them now will never reach us.
 
Last edited:
Receeding galaxies merely redshift into obscurity, they will never suddenly 'disapperar' from view.
 
so they will eventually fade away?
 
Yes, according to current models.
 

Thread 'Does it make sense to build new radio telescopes?'

TL;DR Summary: In 3 years, the Square Kilometre Array (SKA) telescope (or rather, a system of telescopes) should be put into operation. In case of failure to detect alien signals, it will further expand the radius of the so-called silence (or rather, radio silence) of the Universe. Is there any sense in this or is blissful ignorance better? In 3 years, the Square Kilometre Array (SKA) telescope (or rather, a system of telescopes) should be put into operation. In case of failure to detect...
View full post »
Thread 'Could gamma-ray bursts have an intragalactic origin?'

Thread 'Could gamma-ray bursts have an intragalactic origin?'

This is indirectly evidenced by a map of the distribution of gamma-ray bursts in the night sky, made in the form of an elongated globe. And also the weakening of gamma radiation by the disk and the center of the Milky Way, which leads to anisotropy in the possibilities of observing gamma-ray bursts. My line of reasoning is as follows: 1. Gamma radiation should be absorbed to some extent by dust and other components of the interstellar medium. As a result, with an extragalactic origin, fewer...
View full post »

Thread 'Can the signal WOW be explained by the maser effect?'

This hypothesis of scientists about the origin of the mysterious signal WOW seems plausible only on a superficial examination. In fact, such a strong coherent radiation requires a powerful initiating factor, and the hydrogen atoms in the cloud themselves must be in an overexcited state in order to respond instantly. If the density of the initiating radiation is insufficient, then the atoms of the cloud will not receive it at once, some will receive it earlier, and some later. But then there...
View full post »

Similar threads

I How fast were distant galaxies moving?
Replies
7
Views
2K
Stargazing Inquiry Regarding Hypothetical Faster-Than-Light Travel Scenario
Replies
2
Views
2K
I Why on Earth do we not see older stars close to us?
Replies
3
Views
2K
I Cosmological Positioning - How does one determine?
Replies
6
Views
1K
I Moving through space vs sitting in an expanding space
Replies
6
Views
2K
B Can the "creation" of space in the Universe affect the speed of light?
Replies
7
Views
3K
I Upper limit of relativistic spin?
Replies
7
Views
2K
I How do you get to the conclusion that there is accelerating expansion?
Replies
23
Views
2K
B Can we identify the centre of the Universe?
2
Replies
97
Views
12K
I What is the recession speed of a galaxy based on the wavelengths of two stars?
Replies
7
Views
3K

Hot Threads

Recent Insights

Back
Top