A Question About Stars

[Ra]

I have a question for all you science experts. Say a star had a gas giant in close orbit, like Epsilon Eridani does. It's hydrogen and helium, of course, like Jupiter.

The star gets old, and expands. The star's gravity eventually pulls the gas ball in, and it collides with the star.

A: Would the additional fusionable material prolong the stars life at all, and if so, would this be anything significant (ie, a million years or more)?

B: How would this affect other planets in the system? Would the sudden gravity shift of a Jupiter-class planet colliding with its sun cause planets to change/fall out of their orbits? Would it even alter the star's position and make it change course, given a massive enough planet?

Thanks in advance.
- Ra

[Robert Walper]

Well, we can take the following figures:

Sun: 1.989 X 1030 kg (332 830 Earths)

Jupiter: Mass: 1.90 X 1027 kg (317.9 Earths)

Having no expertise in this field, all I can point out is the addition of a Jupiter planet to the Sun's mass would be less than 1/1046 in added "fuel".

[SirNitram]

The collision is more likely to drag material away than add it. Furthermore, just having hydrogen and helium doesn't solve the problem: It must be in the core and accessable. Finally, by the time it's expanded, you're too late: It's now fusing heavier materials, and once it's core is full of iron, game over.

[Hotfoot]

IIRC, the expansion of the star does nothing to alter the mass of the star itself, it's just becoming less dense. In order for the orbit of a planet to decay as a result of stellar expansion, it would have to be pretty darn close. I'm not sure what the orbital radius of the gas giant around epsilon erandi is, but it would most likely have to be under 1 AU in order for the star to gobble it up in expansion.

That said, the effects on the orbits would be altered somewhat, but how much depends on the respective masses of the gas giant and the star itself. If it's a big star and a small gas giant, then not much will likely be changed. If it's a small star and a large gas giant, well, things can get very complicated.

[Surlethe]

IIRC, the expansion of the star does nothing to alter the mass of the star itself, it's just becoming less dense. In order for the orbit of a planet to decay as a result of stellar expansion, it would have to be pretty darn close. I'm not sure what the orbital radius of the gas giant around epsilon erandi is, but it would most likely have to be under 1 AU in order for the star to gobble it up in expansion.

That said, the effects on the orbits would be altered somewhat, but how much depends on the respective masses of the gas giant and the star itself. If it's a big star and a small gas giant, then not much will likely be changed. If it's a small star and a large gas giant, well, things can get very complicated.

I think he's talking about the star expanding so the orbit of the gas giant is inside the star.



AFAIK, the gas giant would tear the atmosphere off the star, not the other way 'round. However, if the gas giant is close enough to be absorbed in the star when it goes red giant, the difference in gravity would be negligible to distant planets in the system, I'd think.

[Caz]

I have a question for all you science experts. Say a star had a gas giant in close orbit, like Epsilon Eridani does. It's hydrogen and helium, of course, like Jupiter.

The star gets old, and expands. The star's gravity eventually pulls the gas ball in, and it collides with the star.

A: Would the additional fusionable material prolong the stars life at all, and if so, would this be anything significant (ie, a million years or more)?

If it prolonged the star's life at all, it would be by a level so insignificant that it could hardly be measured, and that's even assuming that the gas giant is close enough to collide, which it would have to be unless the star was entering red giant phase.

[Ra]

Ah, I see now. So it would have a negligible impact, if at all. Sorry for the n00bish question, guys. I kinda wondered, "Ooh, what would happen if a gas giant sunk into a star? Would it add more fuel?". So, no biggie.
- Ra

[frigidmagi]

Don't worry about it, I'm told questions like these are why we have this forum.

[Josh]

Don't worry about it, I'm told questions like these are why we have this forum.

Yup, exactly. Proliferation of knowledge is the goal.

[Surlethe]

Don't worry about it, I'm told questions like these are why we have this forum.

Yup, exactly. Proliferation of knowledge is the goal.

..assuming we're all correct.

[Shroom Man 777]

We could have a billion gas giants! That'd REALLY prolong life!