How does light act leaving, traveling between, and entering galaxies?

[tm3]

i have a three part question. how does light act leaving, traveling between, and entering a galaxy? we have come to the conclusion that the speed and direction of of traveling light is effected by its surroundings. I'm wondering what that looks like at a galactic scale.

first, leaving a galaxy, can the mass and speed of said galaxy propel the light out in all directions? how fast would that be?

next, is the space outside a galaxy really like a massive vacuum?

finally, could the spinning galaxy pull in the light? how fast? could some of it bounce back out (like if the space shuttle botched it's approach)? how would it act in reference to the stellar population at the time of entry?

 

[Bobbywhy]

tm3, Welcome to Physics Forums!

Light leaving our Sun experiences a gravitational redshift (increase in wavelength). You may think of the light as “climbing out of a gravitational potential well”.
http://www.mrelativity.net/Gravitat...ravitational Effects on Light Propagation.htm

The reverse is true: light experiences an attractive gravitational blueshift (decrease in wavelength) as it approaches a massive body.

Light is bent (curved) as it passes near a massive body. Astrophysicists say “light travels along the null geodesic of curved spacetime”. This is called “Gravitational Lensing”.

Cheers,
Bobbywhy

 

[Chronos]

Galaxies motion is slow relative to the speed of light, so it has virtually zero effect on light. The gravitational influence of anyone galaxy is also basically negligible save where light happens to pass near dense regions [like a black hole]. This would be a rare occurence within a galaxy and virtually non-existent in intergalactic space. Gravitational lensing occurs on large scales involving clusters of galaxies. Intergalactic space is of extraordinarly low density compared to interstellar densities. The overwhelming effect on light over intergalactic distances is due expansion [cosmic redshift].

 

[mfb]

Intergalactic space is of extraordinarly low density compared to interstellar densities.

... and even the interstellar medium is a very good vacuum, many orders of magnitude better than the vacuum in the LHC ring, for example.

Light can fly within, leave and enter a galaxy nearly without any obstruction.

 

[pmacias]

I can provide some insights into how light behaves when leaving, traveling between, and entering galaxies.

Firstly, when leaving a galaxy, the speed and direction of light can be affected by the mass and speed of the galaxy itself. This is because the gravitational pull of the galaxy can bend and distort the path of light, causing it to travel in a curved trajectory. The speed of light, however, remains constant at approximately 299,792,458 meters per second in a vacuum.

Secondly, the space between galaxies is not completely empty. While it is not as dense as the space within a galaxy, it still contains particles such as gas, dust, and dark matter. These particles can also affect the path of light, causing it to scatter or be absorbed.

Thirdly, when entering a galaxy, the spinning motion of the galaxy can also influence the path of light. The rotation of the galaxy can create a gravitational lensing effect, where the light is bent and magnified as it passes through the galaxy. This can also cause some of the light to be pulled towards the center of the galaxy, while some of it may be deflected outwards.

In terms of how fast the light would be affected, it would depend on the specific conditions of the galaxy and the distance between the light source and the galaxy. The speed of light remains constant, but its path may be altered by the gravitational forces within and around the galaxy.

In regards to the stellar population at the time of entry, the light would interact with any objects or particles within the galaxy, potentially being absorbed or scattered. The amount of interaction would depend on the density of the galaxy and the distance between the light source and the objects within the galaxy.

Overall, the behavior of light in relation to galaxies is complex and can vary depending on the specific conditions of each galaxy. However, we can observe and study these interactions to gain a better understanding of the properties and behavior of light in the vast expanse of our universe.