QuestionExploring the Hubble Constant: Calculating Distance and Limitations

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SUMMARY

The discussion focuses on calculating the distance to a galaxy receding at the speed of light using the Hubble constant, specifically a value of 65 km/s/Mpc. The calculation involves converting the Hubble constant to meters per second per megaparsec (m/s/Mpc) and applying the formula v = H * d. The initial calculation incorrectly states the result as 4.6 x 10^4 Mpc, which is corrected by a participant, emphasizing the importance of accuracy in such calculations. The conversation also touches on the implications of recession velocity and the potential visibility of galaxies beyond this distance.

PREREQUISITES
  • Understanding of the Hubble constant and its significance in cosmology
  • Familiarity with the formula v = H * d for calculating distance
  • Knowledge of unit conversions, particularly between kilometers and meters
  • Basic grasp of astronomical distances, specifically megaparsecs (Mpc)
NEXT STEPS
  • Research the implications of the Hubble constant on cosmic expansion
  • Learn about the methods for measuring the Hubble constant, including Cepheid variables
  • Explore the concept of recession velocity and its relationship to redshift
  • Investigate the observable universe and the limitations of visibility beyond certain distances
USEFUL FOR

Astronomers, astrophysicists, and students studying cosmology who are interested in understanding the calculations and implications of the Hubble constant and cosmic distances.

_Mayday_
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The Question

One possible value for the Hubble constant is 65Kms Mpc. Calculate in Mpc, the distance from Earth for agalaxy trallening at the speed of light, [itex]3.0\times10^{8}[/itex]

Attempt

[itex]v=Hd[/itex]

[itex]v=3\times10^8[/itex]

[itex]H= 65Km s Mpc[/itex]

First I will convert the constant to ms so that I have both in S.I. units.

[itex]v=3\times10^8 ms[/itex]

[itex]H= 6.5 \times10^4 ms Mpc[/itex]

Now I will just plug these values in!

[itex]\frac{3\times10^8}{6.5 \times10^4} = 4.6\times10^4 Mpc[/itex]

Question
State what this distance represents.

Answer

This is the distance the galaxy is away from earth?

_Mayday_
 
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Sorry, is this poorly set out? Is there something I have not included?
 
You've made a slip in the final calculation (3x10^8)/(6.4x10^4) is not 4.6x10^4, that aside your method is correct.

The significance of your answer is more than just the distance to a galaxy in this case because the recession velocity is the speed of light.

Could the recession velocity be higher than this?
Could we see any galaxies beyond this one?
 

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