QuestionExploring the Hubble Constant: Calculating Distance and Limitations

In summary, the conversation is discussing the calculation of the distance to a galaxy that is receding at the speed of light using the Hubble constant of 65Km/s Mpc. The calculated distance is 4.6x10^4 Mpc, and it represents the distance the galaxy is away from Earth. The significance of this answer is that it is the distance to a galaxy that is receding at the speed of light, and it raises questions about whether there could be galaxies beyond this one and if the recession velocity could be higher.
  • #1
_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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  • #2
Sorry, is this poorly set out? Is there something I have not included?
 
  • #3
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?
 

Related to QuestionExploring the Hubble Constant: Calculating Distance and Limitations

What is the Hubble Constant?

The Hubble Constant is a measure of the rate at which the universe is expanding. It is denoted by the symbol "H" and is expressed in units of kilometers per second per megaparsec (km/s/Mpc).

How is the Hubble Constant calculated?

The Hubble Constant is calculated by measuring the distances to galaxies and their redshifts (a measure of how much the light from an object has been stretched due to the universe's expansion). By using the relationship between distance and redshift, the Hubble Constant can be determined.

What is the current value of the Hubble Constant?

The current accepted value of the Hubble Constant is approximately 70 km/s/Mpc. However, recent studies have suggested a slightly higher value of around 73 km/s/Mpc. The exact value is still a subject of ongoing research and debate.

Why is the Hubble Constant important?

The Hubble Constant is important because it helps us understand the age and size of the universe. By knowing the rate of expansion, we can estimate how long ago the universe began and how much it has expanded since then. It also plays a crucial role in our understanding of dark energy and the fate of the universe.

What are some challenges in determining the Hubble Constant?

One of the main challenges in determining the Hubble Constant is the difficulty in accurately measuring distances to faraway galaxies. This involves using various techniques and assumptions, which can introduce uncertainties in the final value. Additionally, different methods of measuring the Hubble Constant can yield slightly different results, leading to ongoing debates and research in this area.

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