Creating or reviving our Star?

No one will ever know unless someone can actually do this or have seen this.

First off: my answers here are from my amateur understanding of astronomy/astrophysics. If I do go into physics, it’s not likely to be as an astronomer.
That said, I believe that Jupiter and Saturn together would actually form a brown dwarf, based on the fact that I remember hearing or reading that Jupiter is actually fairly close to being a brown dwarf all on it’s own. (EDIT: It’s my understanding that brown dwarfs don’t really undergo fusion the way a normal star does, they just have a little bit of that going on in the middle, causing a faint glow at most, I might not remember that at all properly though.)
As far as “reigniting” a star with a gas giant: I’m fairly sure it’s impossible. Gas giants are far too small to be fusionable on their own, so compared to a stellar object which once was a fully fledged star in it’s own right, a simple gas giant wouldn’t provide anywhere near enough hydrogen to cause fusion to begin again. I think it might be possible to extend a star’s life span (to a small extent) by throwing a gas giant into it.
(Edit) Again, a professional astronomer, or even a more dedicated amateur astronomer would provide you with a much better (and hopefully more definitive) answer.

No one can know for sure. I do doubt that pushing a gas planet into a dying sun would help in any way, as the energy required to reboot the sun (if that’s even possible) would be way beyond that contained by even Jupiter.

It would not work. Those gas giants don’t have enough density to start a fusion reaction.

Yes, they are just way too small aren’t they. That was my guess.

“If Jupiter and Saturn would be pushed together, would they become a Brown Dwarf or a ignite a Star?”

No. Even Jupiter and Saturn combined are not heavy enough to qualify as a brown dwarf, let alone the smallest possible red dwarf star capable of hydrogen fusion. However, there is some debate about the distinction of a giant gas planet and a very low mass brown dwarf. What criteria to use? Larger brown dwarf could be capable of fusing small amounts of deuterium (like protostars do before they become real stars).

“Could a dying sun be reignited by pushing one of the gas planets into the sun?”

Actually the opposite is true. A dying sun, or rather before it becomes a dying sun extracting gas from it would prolong its life. Pushing gas planets into the sun would force it to do die an early death. It would be even more dramatic when the sun is already dead, i.e. when it has transformed into a white dwarf. Pulling planets into it would finish it off completely, meaning you sort of vaporize the corpse. As soon as the white dwarf reaches the critical mass of 1.44 solar masses (the so-called Chandrasekhar limit) it explodes spectacularly as a type Ia supernova. Nothing remains. No neutron star, no black hole.

Well, from a purely hypothetical viewpoint, if we use a gas giant that is two hundred thousand times larger than Jupitter and push it into a sun that is smaller than our own sun, that might be possible. Who knows? Let’s find a solar system we aren’t using and give it a shot.

@mattbrowne Huh, I wonder what I thought about Jupiter then…
Also, for people who are actually paying attention to this topic and what I’m saying, it’s obvious to me that mattbrowne has been paying more attention to astronomy than I have, so I’m going to tell you all to listen to him.

Thanks guys. Several solid answers. Yes, there seems to be some arguments about the definition of the gas planets, as it was with poor old Pluto.

Technically, an object is considered a planet until it reaches a mass of 13 times Jupiter’s mass, at which point it can sustain thermonuclear fusion and would be considered a brown dwarf. (source)

@evelyns_pet_zebra – The smaller the better. If we divide our Sun into, say 4 pieces we could call it a life extension measure. Pulling more stuff into stars does the opposite. It kills stars. Now if merge dozens of Jupiters until we reach about 10% of our Sun’s mass we got ourselves a new nice little furnance. One that even lasts for dozens of billions of years.

@Harp – The thermonuclear fusion of a brown dwarf is more like a small campfire compared to the blast furnace of a star.

Hey, what I do know well enough to talk about is pluto! First off: pluto never should have been considered a planet, it was never as massive as we expected the 9th planet to be, and even so, it’s still technically a planet, just of a new class of planets/planetoids called Dwarf Planets.
@mattbrowne: right, right, more hydrogen=more mass=>faster fusion. Duh, how’d I forget that.

@astrocom Yes, and I remember reading about a hypothesis that Pluto actually could be a former moon of Neptune.

@oratio – Well, if Pluto is a former moon of Neptune, what are Eris, Varuna and Quaoar? Don’t they all share the fact of being dwellers of the Kuiper Belt dwarf planet family? Sure, Pluto gets closer to the Sun than Neptune at times.

@MrGeneVan

Don’t take this the wrong way, but will you please shut up?

This statement of yours completely contradicts and undermines the entire fundamental principle of science and everything else that pulled us out of the dark ages.

I don’t see any conceivable way to extend the life of a star by adding more mass. An increased mass would increase the rate of fusion of a pre-red giant star. Adding hydrogen to a red giant would most likely do nothing but add mass (the hydrogen wouldn’t burn it would probably never reach the core due to buoyancy and convection—plus it increases the fusion rate). As Matt said once a star has stopped fusing adding mass could be catastrophic.

I always liked the idea of Jupiter becoming a star…..Arthur Clarke made it so believable (of course he magic’ed up enormous amounts of mass to start the fusion process).