(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

After a star like the Sun has exhausted most of the hydrogen in its core it expands and cools to form a red giant. Eventually, when it has exhausted all its nuclear fuel, it sheds its outer layers and contracts and becomes a white dwarf of similar size to the Earth as shown below. Note that the mass of the sun is 2 × 10^{30}kg, the radius of the Earth is 6,380 km and Newton's gravitational constant G is 6.67 × 10^{–11}Nm^{2}kg^{–2}.

Light leaving the surface of a star of mass M and radius R is stretched in wavelength (i.e. "gravitationally red-shifted") by an amount Δλ/λ = GM/(Rc^{2}) where c is the speed of light.

Calculate the gravitational red shift for light leaving the surface of the white dwarf

3. The attempt at a solution

I tried substituting the values into the formula Δλ/λ = GM/(Rc^{2}) but that didn't produce the right answer...

Then I tried using the "scape speed" equation is given by

[tex]v_{esc}=\sqrt{\frac{2GM}{R}}[/tex]

Where G is the gravitational constant. M is the mass of the white dwarf and R is its radius converted to meters.

But this didn't work either. The right answer has to be 0.000279. Can anyone explain to me how the got this answer? I have an exam tomorrow...

Thanks in advance

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Gravitational red shift

**Physics Forums | Science Articles, Homework Help, Discussion**