The mass of the sun at its beginning

[elegysix]

Hi guys, so I know the sun is losing mass because it is radiating energy away. This leads me to wonder about some things - I have been trying to figure out what the mass of the sun was ~4.5 billion years ago (current age of the sun).
Also I am interested in knowing what the mass will be ~6.5 billion years from now, when it is entering the white dwarf stage.

Does anyone know it? Or know how to figure it out? I am assuming it involves an exponential decay function, because of the familiar relationship between luminosity and mass.

Thanks!

 

[e.bar.goum]

Well, back of the envelope, the mass loss will be at most 0.7% over the entire age of the sun. So the curve probably won't be very interesting if you just take into account mass loss due to E=mc². :)

(This is assuming that the sun starts off at 100% H and turns into 100%He at the end of it's life via the pp chain. Not at all true, it's an upper-ish bound.)

Most mass loss by the sun is done by the solar winds, which amounts to ~0.01% over the life of the sun so far, or 7 billion tonnes an hour. When the sun enters the Red Giant phase, the mass loss will get a bit more ... explosive.

 

[Ken G]

The only time the Sun loses a significant amount of mass is most likely after it is finished burning H into He. Then, in late stages of evolution, it is believed it will lose roughly 50% of its mass and create what is called a "planetary nebula", and the other half will stay behind as a carbon/oxygen white dwarf. There is some chance the Sun had a much stronger stellar wind when it was very young, but it's hard to imagine that it could have sustained a strong wind long enough to affect its mass significantly. As you have heard, the mass lost to H fusion is pretty negligible.

 

[Fantasist]

Does anyone know it? Or know how to figure it out? I am assuming it involves an exponential decay function, because of the familiar relationship between luminosity and mass.

It looks like you misunderstood something here: the mass-luminosity relationship only holds for stars on the main-sequence (i.e.. the sun as it is today). It does not enable you to relate the mass to the luminosity throughout the star's life (even if you knew one of the two).