World Science Scholars
2.4 The Hubble Constant
demonstration

Edwin Hubble showed that the receding speed and the distance of a cosmic body were related by $v=H_0 d$, where $H_0$ came to be known as the Hubble constant. To calculate the age of the universe, we can measure distances and velocities of nearby supernovae, plot them, and solve for $H_0$. In this demonstration, you are provided with real NASA data of distances and red-shifts for six supernovae: $\array{ \underline{\text{Supernova}} & \underline{\text{Distance (Mpc)}} & \underline{\text{Red-shift (z)}} \\ \text{1995D} & 36.14 & 0.008 \\ \text{1995E} & 55.72 & 0.012 \\ \text{1996C} & 145.88 & 0.028 \\ \text{1990af} & 215.77 & 0.050 \\ \text{1992bs} & 335.74 & 0.064 \\ \text{1992aq}& 463.45 & 0.101 }$

In astronomy, scientists use red-shifts to infer the velocity of a cosmic body. Red-shift is an apparent increase in the wavelength of light due to the Doppler effect. However, we wish to plot receding speed — not red-shift — as a function of distance. To calculate receding speed, we multiply each red-shift value by the speed of light, $c=3 \times 10^5$ km/s.

Drag the slider below to set the slope of the line to best represent the data points. The slope of this line, $\frac{v}{d}$, will be the Hubble constant $H_0$. Then, to convert from kilometers to parsecs, we multiply $\frac{1}{H_0}$ by $3.09 \times 10^{19}$ km (the number of km in a megaparsec) to find the age of the universe. Keep in mind we aren’t accounting for acceleration here.

The accepted value of the Hubble constant is roughly 70 (km/s)/Mpc and the accepted value of the age of the universe is approximately 13.8 billion ($$1.38\times 10^{10}$$) years. How do the numbers we calculate from these six supernovae compare?

×

## Share with others

Select this checkbox if you want to share this with all users

Select Users

Enter the usernames or email IDs of the users you want to share with