I've been working on it, and I think this may work, M = z(rc^2)/G , where "z" is the redshift, do you think this would work, it seems to be giving around the correct result, but I would much prefer someone wiser to review and correct...Orodruin said:The amount of red-shift is computed by looking at the position of spectral lines and comparing to the proper frequencies of these lines. You can then compute the gravitational mass using the predicted gravitational redshift and equaling it to the observed redshift. For details on how to compute the gravitational redshift, I recommend reading an introductory text on general relativity. There are several conceptual pitfalls and it really requires more careful writing than you will generally find in a forum. The same goes for cosmological redshift, while doppler shift is essentially a special relativistic effect. Neither the cosmological shift or doppler shift depend on the mass of the star. If you do not have access to an introductory textbook, I suggest starting at Wikipedia.
OK thank you for the help and advice :)Orodruin said:Yes, this is true under some assumptions. Mainly, the Schwarzschild metric must be a good description of the space-time around the star and the radius of the star must be much larger than the Schwarzschild radius of an object with the same mass. For normal stars, this is generally a pretty good approximation.
And note you are actually getting M/r, not M, by observing z. That wouldn't work so well for giant stars, because M/r is very small and hard to detect, and it's not that helpful for main-sequence stars, because they all tend to have a similar M/r so you'd need to detect z very precisely to distinguish them, but the z would only be about 1 part in 100,000. But it is very handy for white dwarfs, because white dwarfs have a mass-radius relationship, such that r is proportional to M-1/3, so M/r is proportional to M4/3, so M is proportional to z to the 3/4, and z is much larger and easier to detect. So it's used as a good way to get the mass of a white dwarf.LachyP said:I've been working on it, and I think this may work, M = z(rc^2)/G , where "z" is the redshift, do you think this would work, it seems to be giving around the correct result, but I would much prefer someone wiser to review and correct...
The redshift of a star is directly related to its mass through the Doppler effect. As the star's mass increases, its gravitational pull becomes stronger, causing the light it emits to be stretched to longer wavelengths (redshifted) as it travels through space.
Yes, the redshift of a star can be used to estimate its mass, but it is not the only factor that needs to be considered. Other factors, such as the star's luminosity and temperature, also play a role in determining its mass and must be taken into account in the calculation.
The mass of a star can be calculated using the equation M = cz/G, where M is the mass, c is the speed of light, z is the redshift, and G is the gravitational constant. This equation is derived from the relationship between redshift and mass in the Doppler effect.
The mass of a star calculated from redshift is typically expressed in terms of solar masses, which is the mass of our Sun. This unit is convenient because it allows for easy comparison between the masses of different stars.
Yes, there are limitations to using redshift to calculate the mass of a star. This method assumes that the star is in a stable, non-rotating state, and that there are no other factors affecting its redshift. In reality, stars are constantly evolving and can have complex motion and interactions, making it difficult to accurately determine their mass using redshift alone.