# Blue shift galaxies and the expanding universe

• nite owl
In summary, galaxies with blueshifts have smaller recession rates than galaxies without blueshifts. This does not contradict the idea of an expanding universe.

#### nite owl

We are told the universe is expanding because galaxies are red shifted and that it is a doppler effect. Do blue shifted galaxies contradict the idea of an expanding universe?

nite owl said:
We are told the universe is expanding because galaxies are red shifted and that it is a doppler effect. Do blue shifted galaxies contradict the idea of an expanding universe?

No the blueshifts of some galaxies only correspond to small (few 100 km/s) random velocities---don't contradict the overall average pattern of recession rate.

If you really want to get to understand redshift and the standard cosmological model then a good thing to do is practice with this calculator
http://www.uni.edu/morgans/ajjar/Cosmology/cosmos.html

to get some experience of what recession rates (and distances) are associated with which redshifts.

To use it you first enter the three principal parameters in the three boxes over on the left labeled "matter fraction", "cosmo constant", and "Hubble". Standard numbers to use are .27, .73, and 71.

Then put in a redshift, like 8.5 (the redshift of a galaxy measured last year, since then some more distant galaxy may have been discovered) and press calculate.

It will give you the distances and recession rates.

You will see that the recession rates are mostly much larger than a few 100 km/s.

(Considering that 300 km/s is only 1/1000 of the speed of light!)

The distance definition commonly used by redshift calculators (like this and like Ned Wright's) is the same distance used in stating the Hubble Law v = H d
where v is the recession rate and d is the distance. It is the "freezeframe" distance you would measure by any ordinary means if you could freeze the expansion process, so that the distance would not change while you were trying to measure it.

Have a look at Morgan's "cosmos calculator" and see if works for you. Please let me know if you have any trouble.
The link is in my signature, or just google "cosmos calculator" and you'll get it.

What blue shifted galaxies do you have in mind that are not members of the local group?

## 1. What is blue shift in galaxies?

Blue shift in galaxies refers to the phenomenon where light from an object in space appears to have a shorter wavelength, or is shifted towards the blue end of the color spectrum. This occurs when an object is moving towards the observer, causing the light waves to be compressed and appear bluer.

## 2. How does blue shift relate to the expanding universe?

The blue shift in galaxies is a result of the expansion of the universe. As the universe expands, galaxies that are further away from us appear to be moving away faster, causing their light to be shifted towards the blue end of the spectrum.

## 3. What causes the expansion of the universe?

The expansion of the universe is caused by a force called dark energy. This force is currently not fully understood, but it is believed to be responsible for the accelerating expansion of the universe.

## 4. Can blue shift be used to measure the rate of expansion of the universe?

Yes, blue shift can be used to measure the rate of expansion of the universe. By measuring the amount of blue shift in light from distant galaxies, scientists can calculate the velocity at which these galaxies are moving away from us and use this information to determine the rate of expansion of the universe.

## 5. Is the blue shift in galaxies constant?

No, the amount of blue shift in galaxies is not constant. This is because the rate of expansion of the universe is not constant and is actually increasing over time due to the presence of dark energy. This means that the blue shift in galaxies will also increase over time.