1
$\begingroup$

How much does the gravitational redshift change a neutron star emission spectra, thus altering an estimate of its surface temperature? I remember some tv-shows talking about Italian pasta when talking about neutron stars....does this imply neutron stars are not all of the same density, so gravitational redshift differs depending on differences in densities between neutron stars?

$\endgroup$

1 Answer 1

1
$\begingroup$

The standard gravitational redshift formula applies to neutron stars.

This means that if a distant observer observes a spectral feature that was emitted at a rest wavelength of $\lambda_0$ from the NS surface, then it will be observed at a wavelength $$\lambda = \lambda_0\left(1 -\frac{2GM}{Rc^2}\right)^{-1/2}\ ,$$ where $M$ and $R$ are the neutron star mass and radius (actually the Schwarzschild $r$ coordinate of its surface).

Since establishing a temperature from a blackbody spectrum involves finding the peak wavelength, then the observed temperature is reduced by $$T = T_0\left(1-\frac{2GM}{Rc^2}\right)^{1/2}\ .$$

The ratio $M/R$ probably does vary a little bit (up to a factor of 2) between the most and least massive neutron stars. Roughly speaking, $M/R \propto M$, since the equilibrium radii of neutron stars are quite insensitive to their mass (in most models).

"Nuclear pasta" occurs in neutron star interiors and doesn't affect radiation from their surfaces. It also has little effect on their structural properties.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.