# Could we recharge the sun's “batteries”?

The Sun is 4.6 billion years old and is estimated to live in this stable phase another 4.6 billion years.

Since the Sun is a star, once it reaches the end of its lifetime, it will become a supernova, at least from what I've learned. From this link:

They can only happen when an aging massive star can no longer generate energy from nuclear fusion and undergoes a rapid gravitational collapse. This collapse releases potential energy that heats up and throws off the outer layers of the star in the form of an enormous explosion.

Since the Sun clearly fits the criteria for a supernova to occur (aging, massive), does this mean we could recharge the sun's batteries by refueling it with items that create energy from nuclear fusion?

I'm pretty well aware this is probably a crazy idea, but what I'd really like to know is, how feasible could it be?

• And the premise that the sun will become a supernova is at least questionable. – Alexander Jul 7 '14 at 23:23
• The sun isn't massive enough to create a supernova. The cut-off is somewhere around 8 times the sun's mass (i.e., a star with mass less than that won't blow up). – Kyle Kanos Jul 8 '14 at 0:43

As you said, a star explodes as a supernova when it runs out of fuel for nuclear fusion. The Sun is unlikely to go supernova, instead it is most likely to end as a red giant, then shed its outer layers and result in a white dwarf.

Leaving that aside, if you want to extend the lifetime of a star, the key thing to do is increase the amount of time before it runs out of fuel. Your first intuition of "add more fuel!" (adding more fuel means adding more Hydrogen) is actually the worst thing that you could do. More massive stars (the ones with the most fuel) are actually the ones that burn out fastest. This is because, although they have more fuel, the rate at which they burn that fuel grows very rapidly with mass. A small star with a little bit of fuel will burn that fuel very slowly and last a long time, while a more massive star will have more fuel, but burn through it quickly and have a shorter lifetime. If you want the Sun to last longer you need to take away a lot of Hydrogen. Probable side effects include reduced light & heat output from the Sun, resulting in a global, permanent ice age.

The Sun is far too small to undergo such a supernova explosion. What it will do is swell up to a Red Giant, engulfing Mercury, Venus, and possibly the Earth (we'll be deep fried whether or not the Sun actually engulfs us).

No amount of energy we could add to a star would have more than a tiny effect on what it's doing. It's just too big.

• I was contemplating adding another answer to emphasize on that point - ''we'll be deep fried''. +1 for your answer. So, OP need not worry about recharging the sun. We won't be there to miss the sun! – 299792458 Jul 9 '14 at 5:57

First off, our sun isn't massive enough to go supernova. It would take a star equivalent to five of our own to reach the mas necessary for supernova to occur.

Secondly, no. Your idea would not work at all. Nuclear weapons are no where near the same level of energy as a start and could not extend its life.

Third, the sun undergoes nuclear fusion while nuclear weapons utilize nuclear fission which are completely opposite effects.

• I think the lower mass limit for a supernova is about 8 solar masses. Plus, modern Hydrogen bombs do utilize fusion. It is the older atomic bombs that are based on fission – Jim Jul 7 '14 at 23:18
• Granted, some nuclear weapons do use fusion. A lot of them still are based on fission technology. And I think the mass requirement actually depends on the type of star, for instance the Chandrasekhar limit is 1.44 solar masses. – jkeuhlen Jul 7 '14 at 23:22
• The Chandrasekhar limit is the limit on the stellar remnant, the white dwarf. If the WD accretes more mass, or would be formed more massive than this, a neutron star is produced instead. The progenitor star is more massive than the remnant. A $3 \rm M_\odot$ star can produce a $1\rm M_\odot$ remnant – Kyle Oman Jul 7 '14 at 23:23
• @Kyle thanks for the clarification. Obviously I'm not an astro guy :) – jkeuhlen Jul 7 '14 at 23:24