CrazyNeutrino said:
A better model for star aging
Working out the age of any given star in the night sky can be a very difficult task, and estimates are easier to make based on readings from groups rather than individual objects. A new model might significantly improve the situation, providing a conceptual framework to explain the rotation of stars, the intensity of their stellar winds and their X-ray emissions, arriving at a much more accurate estimate of age.
more…
My knee-jerk reactions are:
1) We certainly need one
2) I’ll believe it when I see it
I’ve done a bit of stellar modelling myself, just using a free web application. They do an excellent job in some respects, such as relating the neutrino flux from the core to the overall luminosity. There’s some variability in actual stars around the predictions that nobody has yet got a handle on. For example given the mass, age and metallicity of a main sequence star, the luminosity can be out by a factor of two. The biggest uncertainty is in what the opacity is, the opacity is independent of the amount of hydrogen and helium in a star and depends on the elements heavier than helium, which is a minor component in most stars. so the opacity depends on minor components but has a dominant effect on star diameter and speed of evolution. A second uncertainty comes from the use of the mixing length model of turbulence, in terrestrial fluid dynamics that method was abandoned as being unreliable back in the late 1970s, but remains in use for stellar modelling. A third uncertainty comes from the 1-dimensionality of most simulations, star behaviour becomes 2-D when rotation is taken into account and 3-D when sunspots are taken into account. Also, thermal convection within the star is inherently a 3-D process, it’s largely the need to fudge this that leads to the retention of the fudge factor possible using outdated the mixing length model.
A fourth uncertainty comes in as the modelling of stellar atmospheres, classical stellar models are incapable of handling realistic conditions on the surface of the star unless coupled to s separate mathematical model of the star’s atmosphere. A fifth uncertainty comes from rapid variations with time, in pre-main sequence stars and post red-giant stars the evolution is rapid, and that is not well modelled by stellar models. For example, no model that I’ve heard of is capable of correctly modelling the pulses of mass loss that occur as the star progresses along the asymptotic giant branch.
The margin error of “billions of years” mentioned in the article refers to the lack of a one-to-one relationship between mass, age, metallicity and luminosity that I mentioned above.
> working out how rotation, magnetic fields, X-ray activity and loss of mass are linked and affect one another.
I agree. I think this is new.