Were red dwarfs once as luminous as the Sun?

[MathematicalPhysicist]

What is the empirical evidence that the red dwarves we observe nowadys were once like our sun in magnitude and luminosity?

Thanks in advance for any reference.

 

[NobodySpecial]

Observational evidence from a few billion years ago is rather scarce.
Stellar evolution is based on modelling and nuclear physics along with observations to fix the parameters. If you model the life of a star and the predicted numbers of stars of each type at a point in time match the number of each type we see now then the model is probably good.

 

[MathematicalPhysicist]

So it's kind of ad hoc isn't it?
Like every modelling in science, I guess.

 

[Vanadium 50]

What is the empirical evidence that the red dwarves we observe nowadys were once like our sun in magnitude and luminosity?

None, because red dwarfs are not evolved yellow dwarfs.

 

[Chronos]

Red dwarfs are between .08 and .4 Msun [solar mass] stars. They are main sequence hydrogen burning stars, but much cooler and less luminous. The are also much longer lived. A star of 0.1 Msun would have a lifetime of 300 times that of the Sun, or about 3 trillion years. Because of their low luminosities, red dwarfs are fully convective. Their core energy is carried to the surface by gas currents. This also fully mixes hydrogen and helium so they can burn all of their hydrogen. When a red dwarf has used up all its hydrogen, it will simply collapse to form a helium white dwarf. It bypasses the red giant phase typical of larger stars [which incidently is the fate of our sun].

 

[granpa]

http://casswww.ucsd.edu/public/tutorial/HR.html

http://www.astronomynotes.com/starprop/s13.htm

http://www.dur.ac.uk/ian.smail/gcCm/gcCm_intro.html

 

[Nabeshin]

What is the empirical evidence that the red dwarves we observe nowadys were once like our sun in magnitude and luminosity?

Thanks in advance for any reference.

Just for general knowledge.. the vast majority of temporal evolution in astronomy is deduced not from direct observation but from large representative samples. That is, we have nowhere near enough time to stare at a star as it evolves along the main sequence. Rather, we can look at millions of stars which presumably were all created out of similar environments, and (assuming they all evolve similarly) get a picture of the temporal evolution by seeing groups of stars which are young, medium, and old. See: HR diagram.

If you think this is not a valid strategy of deduction, I strongly suggest you look into it more.

 

[twofish-quant]

What is the empirical evidence that the red dwarves we observe nowadys were once like our sun in magnitude and luminosity?

They weren't. I think you mean red giants.

Anyhow, what you can do is to take a snapshot of all of the stars in a cluster. Since all of the stars in a cluster were born at roughly the same time, you get a snapshot of how stars at a certain fixes age look like, and what you see are stars on the main sequence up to a certain mass, and then they turn off into red giants.

 

[Chronos]

But, our deductions about stellar evolution appear to be sound. We deduce their properties based on particle physics and observation. We have detected no significant observational deviations from particle physics models to date.

 

[Vanadium 50]

There's relatively little particle physics involved. You have some nuclear physics, but it's really hydrostatics, thermal transport and convection that you need to explain stars. The only thing that really involves particles is the photon-electron scattering that results in opacity.

 

[SpiffyKavu]

We have also been able to look inside a good fraction of the sun using helioseismology. This is analogous to our use of seismology here on Earth to determine the interior structure of our planet. We have found that our models of the sun's interior are more or less correct.

 

[twofish-quant]

But, our deductions about stellar evolution appear to be sound. We deduce their properties based on particle physics and observation. We have detected no significant observational deviations from particle physics models to date.

That's because when we observe deviations we change the model (i.e. what happened with solar neutrinos). Not that there is anything wrong with that...

One question that comes up is how robust a result is. You can run a solar simulation and then ask the computer what you have to do so that a one solar mass star *doesn't* end up being a red giant. It turns out that you have to radically change things in ways that are likely to be excluded by experiment.

Also, based on globular clusters, we think we have a good handle on how single star one solar mass stars work. For massive stars, and what's more for massive stars with extremely low non-hydrogen/helium content, there is still a lot we don't know.