How can the galaxies travel faster than sound and light?
The universe is a very dynamic place.Once thought to be static and unchanging, the cosmos Royals with activity.
Clusters of galaxies spin and twirl in a dance of unprecedented scale and all of it occurring and an ever-expanding ballroom.
But how do we know this?
How do we know these galaxies are interacting in such a way?
We know the stars and galaxies are moving because we can see their light compress and expand as they move through the heavens. A star or galaxy moving towards us has a spectrum, that is shifted to the blue as compared with a stationary spectrum and red shifted if the object is moving away.
There are three ways light from celestial objects can be shifted and the amount is usually denoted by a dimensionless number, Z:
The first way is known as Doppler shift and is due to the proper motions of the stars and galaxies relative to each other, for example the Andromeda galaxy has a spectrum that is blue shifted because it is heading straight towards our galaxy.
Doppler ships are usually small with avalue of Z less than one.
Second way light can be shifted is called a gravitational ship, and it is usually caused by light leaving a luminous body that is near an object with a large mass, such as a black hole or a neutron star.
The third way is the most interesting, cosmological red-shift, and it is caused by the expanding universe.
Photons leaving a distant galaxies are stretched by expanding space time always towards
the red and the amount of shift is directly related to his distance from us
Astronomers know which of these three is in effect by the object being observed.
A moving nearby star or galaxy will exhibit shift due to the Doppler effect.
A star or other luminous object near something with lots of mass will have its spectrum shift to do gravity, while very distant galaxies will always have a red-shift and it will be due to universal expansion.
So how can there be measured red-shifts greater than the speed of light?
It turns out that an object moving at the speed of light would have a measured red-shift of about 1.4 and would like 4200 million parsecs away.
Two galaxies, moving relative to each other, are bound by the laws of relativity, so 1.4 will be about the largest Doppler red ship that can be record and the photons left that star or galaxy 4.6 billion years after the Big Bang.
Any galaxy moving away from us with a Z greater than 1.4 is moving away from us at faster than the speed of light.
Paradoxically, the Hubble Space Telescope routinely measures galaxies with cosmological redshift of 8 or more.How is as possible?
While the laws of relativity do limit the speed of two or more galaxies moving in relation to one another, the expansion of space-time is not bound by this limit.
Relativity places no limits on the speed with which creation can expand.
The farther galaxy is from us, the faster is traveling.
No limits the most distant galaxies measured so far are around Z equal eight the light left those galaxies when the universe was only 600 million years old.
So how can we possibly see the light from these galaxies if they are traveling so fast?
The answer is that the motion of the galaxy now has no effect whatsoever on the light emitted billions of years ago.
The photon that is traveling towards us has no knowledge of what the galaxy does after it leaves, it is affected only by the increasing amount of space time as it travels.
At the moment photons are emitted from very distant galaxies, they are not traveling faster than light. But as the galaxy continues to recede, and that has picked up speed until its red-shift is greater than 1.4 many photons would not be able to outrun the galaxy.
We would observe the galaxy freeze, then slowly fade away.
Our current value of the Hubble constant says that for every megaparsec of distance between two galaxies, the apparent speed at which the two of them move apart increases by 71 km/h second the implications for this rather bleak.
Because of universal acceleration, any galaxies that are currently moving away from us at faster than light, will always be doing something.
Once a galaxy says its last goodbye, we will never hear from it again.
Someday, as I recall, the Milky Way galaxy will "eat" it's smaller neighbor Andromeda, after we collide with each other.
Your memory, as with most, is fallible. The Andromeda Galaxy is much larger (~220,000 light years across and the largest galaxy in the local group) than the Milky Way Galaxy (conservative estimates are 100,000 to 120,000 light years across with more liberal estimates of 150,000 to 180,000 light years across) and 'someday' is estimated to be 3.75 to 4 billion years away from the expected collision of the two. The galaxies are predicted to merge into a giant elliptical -or- large disc galaxy after the proverbial galactic dust settles. With that said, there is a small possibility the Solar System could be ejected into the darkness as a rogue or join Andromeda in a dance before resting in Milkomeda or Milkdomeda (proposed names for the new galaxy that no one will likely be around to entertain at the point of fruition).
Simply Great Information and Presentation
Thanks