In: Physics
A galaxy’s calcium-H line – normally located at 3968.4673 Å – is observed to have a wavelength of 4074.995 Å. How far away would you calculate this galaxy to be, in Mpc, using a Hubble’s parameter of 72.5?
|
106 |
||
|
8,047 |
||
|
73 |
||
|
111 |
||
|
240 |
||
|
None of the above is close |
Solution:-
Rest wavelength is (
)
= 3968.4673
Observed wavelength is (
)
= 4074.995
Hubble Constant given = 72.5 km/sec/Mpc
Now in order to get recession velocity galaxy we use doppler shift

where v is recession velocity, ? is the rest wavelength, ?? is how much the line has shifted due to the Doppler effect, c = 3×105 km/s is the speed of light.


So recession velocity is:-





By Hubble's Law-

Now substituting values of
and
-



So the answer is option D.