Confusion with conversion for the Hubble Constant

In summary, the conversation discusses the conversion between estimates in terms of h50 or h70 and H0 = 100 h Mpc-1 kms-1. The equation for this conversion is h = H0 / 100 kms-1 Mpc-1, and the value of h is a dimensionless version of the Hubble constant, representing the ratio of H0 to a reference value of 100 km s-1 Mpc-1.
  • #1
Radiohannah
49
0
Hello!

I want to get my data in terms of h70 -1

Sometimes the estimates are in terms of h50 or h70, and I know how to convert those just fine.

However, sometimes they give H0 = 100 h Mpc-1 kms-1 instead...

My question is, what is this in terms of h?

I know that the relation is

h = H0 / 100 kms-1 Mpc-1

So, would I be right in thinking that it is as straight forward as h=H0 for this specific case or am I being silly

Thankyou! :)
 
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  • #2
Radiohannah said:
So, would I be right in thinking that it is as straight forward as h=H0 for this specific case

:confused: Absolutely not, because as you yourself have noted, h is actually equal to:

Radiohannah said:
h = H0 / 100 kms-1 Mpc-1
 
  • #3
Hah. I totally figured it out.

I was confused originally because I did use that equation, but got h=h

I thought h=70, rather than H0 = 70

:(

So is 'h' basically just a fraction then? I understand now.

Gah. Thanks
 
  • #4
Radiohannah said:
Hah. I totally figured it out.

I was confused originally because I did use that equation, but got h=h

Which is true! But not that informative I guess.

Radiohannah said:
I thought h=70, rather than H0 = 70

Right, so that's where your misconception was. That value of H0 corresponds to h = 0.7

Radiohannah said:
So is 'h' basically just a fraction then? I understand now.

Exactly, you got it now! The parameter h is a dimensionless version of the Hubble constant. It is H0 normalized to a reference value of 100 km s-1 Mpc-1. So h is a fraction...it tells you the ratio of H0 to that reference value.
 
  • #5


Hello!

I understand your confusion with converting the Hubble Constant into different units. It is important to be precise and accurate when dealing with scientific data.

To answer your question, yes, you are correct in your thinking that h=H0 for this specific case. The Hubble Constant, H0, is defined as the current expansion rate of the universe and is typically measured in units of kilometers per second per megaparsec (km/s/Mpc). This can also be written as h=H0/100, where h is a dimensionless number representing the Hubble Constant in units of 100 km/s/Mpc.

So, when given H0=100h Mpc-1 kms-1, you can simply divide by 100 to get h=H0/100, which would give you the value of h in units of km/s/Mpc. This can then be converted to h70 by multiplying by 70, or h50 by multiplying by 50, depending on which units you need.

I hope this helps clarify your confusion. Remember, it's always important to double check your conversions and units to ensure accuracy in your data. Keep up the good work!
 

1. What is the Hubble Constant and why is there confusion with its conversion?

The Hubble Constant is a measure of the rate at which the universe is expanding. It is calculated by measuring the speeds and distances of galaxies. There is confusion with its conversion because different methods and data sets can produce slightly different values for the constant.

2. How is the Hubble Constant typically expressed and what units is it measured in?

The Hubble Constant is typically expressed in units of kilometers per second per megaparsec (km/s/Mpc). This means that for every megaparsec (3.26 million light years) of distance, a galaxy is moving away from us at a certain speed in kilometers per second.

3. Why is it important to accurately determine the Hubble Constant?

Accurately determining the Hubble Constant is crucial in understanding the age, size, and future of the universe. It helps us determine the expansion rate of the universe and the amount of dark energy present, which can shed light on the ultimate fate of the universe.

4. How is the Hubble Constant calculated and what factors can affect its value?

The Hubble Constant is calculated using a variety of methods, such as measuring the redshift of distant galaxies or observing the cosmic microwave background radiation. Factors that can affect its value include the distance measurements of galaxies, the type of data used, and the cosmological model assumed.

5. What is the current estimated value for the Hubble Constant and how does it compare to previous estimates?

The most recent estimate for the Hubble Constant is around 73 km/s/Mpc, with a margin of error of about 2.5 km/s/Mpc. This is slightly higher than previous estimates, which ranged from 67-72 km/s/Mpc. However, the discrepancy between different methods and data sets has led to ongoing debates and research to further refine our understanding of the Hubble Constant.

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