Are You Using the Correct Formula to Convert Redshift to Megaparsecs?

In summary, the formula being used to convert redshift to megaparsecs is z x c = H x d, where H is taken to be 71km/s/Mpc and c is 299,792.46 km/s. A redshift value of 0.1 yields a distance of 1.377 Billion Light years (422.2429 Mpc), which is expected. However, a redshift value of 10 yields a much larger distance of 137.717 Billion Light years, which is likely due to the non-linear nature of the expansion of the universe. A more accurate formula is recommended, such as the one mentioned in the provided review article.
  • #1
Sagan369963
4
0
z x c = H x d is the formula I am using to try to convert redshift to megaparsecs, where H I'm taking to be 71km/s/Mpc and c as 299,792.46 km/s. When I plug in .1 for z I get 1.377 Billion Light years (422.2429 Mpc), which sounds right. But when I plug in 10 for z I get the huge distance of 137.717 Billion Light years. Is that because of the comoving universe? I'm really just after the light travel time distance, not really where the galaxy is now. Am I using the wrong formula?
 
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  • #2
You are using linear relation v=cz, which is not good at larger distances. Try here, just plug redshift value and you will have light travel time distance.
 
  • #3
To expand a little on Calimero's response:
The equation you are using is the linear approximation of the full expression for the expansion of the universe (given a particular cosmology). Here is an excellent review article which should answer your question in detail http://arxiv.org/abs/astro-ph/9905116
 

FAQ: Are You Using the Correct Formula to Convert Redshift to Megaparsecs?

What is the Redshift to Megaparsec Formula?

The Redshift to Megaparsec Formula is a mathematical equation used by astronomers to calculate the distance to faraway objects in the universe based on their observed redshift. It takes into account the Hubble constant, the speed of light, and the redshift value of the object.

How is the Redshift to Megaparsec Formula derived?

The formula is derived from the Hubble's law, which states that the further away a galaxy is from us, the faster it appears to be moving away from us. It is also based on the Doppler effect, which explains the shift in the wavelength of light emitted by an object that is moving away from us.

Can the Redshift to Megaparsec Formula be used for all objects in the universe?

No, the formula is only applicable to objects that are moving away from us, as they exhibit a redshift. Objects that are moving towards us will have a blueshift, and a different formula must be used to calculate their distance.

Are there any limitations to the Redshift to Megaparsec Formula?

Yes, the formula is based on the assumption that the expansion of the universe is linear and that the Hubble constant is constant over time. However, recent studies have shown that the expansion of the universe is accelerating, which can affect the accuracy of the formula.

How is the Redshift to Megaparsec Formula useful in astronomy?

The formula is a vital tool for astronomers to measure the distance to objects that are too far away to be measured by other means. It allows us to study the evolution of the universe, the distribution of galaxies, and the rate of expansion of the universe.

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