Recent content by Lilian Sa

What I've done is using the TOV equations and I what I found at the end is: ##e^{[\frac{-8}{3}\pi G\rho]r^2+[\frac{16}{9}(G\pi\rho)^{2}]r^4}-\rho=P(r)## so I am sure that this is not right, if someone can help me knowing it I really apricate it :)

But it was given in the question that ##a## depends on ## t ## , I don't know if its legal to suppose that it does not depend on ## t ##. :(

I don't think so, because we have to get a diagonalized metric with the four coordinates, which include Y or the transformed Y.

I'll try rhis today, hope it will work. thanks very much!

but this additional cross term we have to equate it to zero and then we get the expression equal to zero, but that doesn't help :( or I am wrong?

This is what I got at the end: ## ds^2=-dt^2(1-\partial_tF)+d\tilde{x}^2+(\partial_yF+2a^2\partial_yF)dy^2+dz^2+d\tilde{x}dy(sa^2+2\partial_yF)+dtdy(2a^2\partial_tF+2\partial_tF\partial_yF)+d\tilde{x}dt(2\partial_tF) ## that means that I got ##F ## does not depend on any coordinate! but this is...

I posted a thread yesterday and I think that I did not formulated it properly. So I have a metric ##{ds}^{2}=-{dt}^{2}+{dx}^{2}+2{a}^2(t)dxdy+{dz}^{2}## I was asked to find the the coordinate transformation so that I can get a diagonalized metric. so what I've done is I assumed a coordinate...

Thank you all, I saved all of them :)

hey there :) So I had a homework, and I was asked to diagonalize the metric ##{ds}^2=-{dt}^2+{dx}^2+2a^2(t)dxdy+{dz}^2## and to find the coordinate transformation for the coordinates of the new metric. so I found the coordinate transformation but the lecturer said that what I found is a...

thank you :)

yes rho depends on time

Ok I am on it now, but why we have in the answer (t_*-t)^(2\3)

replace r in R.

Mentor note: Fixed the LaTeX It is a collapse of a non relativistic star under its own gravity. ##M(R)=4\pi \int\rho(t)r^2dr##

let me be honest, both. I just did not understand it. In the numerator there is M as a function of R, and in the denominator there is the function R.