You mean like Mars is our sister planet so to speak? In that case, it's entirely possible. Especially if you expand it to include the entire universe.

There was a theory popular some years ago that the sun has a far-flung companion, nicknamed Nemesis, that periodically -- every few tens of millions of years -- approaches the inner solar system perturbing comets and asteroids, to account for impact events causing mass extinctions. There is little evidence, however, to support this.

I would say that it would be incredibly unlikely that the sun has a twin. For the sun to have a twin would require there to be another star gravitationally bound within our solar system. This would be easy to spot as you would have a bright star that would be incredibly bright. Also the gravitational pull of the star itself would great very noticeable pulls on the planets themselves as in our solar system roughly 99.8% of the total mass (of the solar system) is just in our sun alone. You can and do get stars much smaller than ours, but they would significantly outweigh any planet in our solar system as they have a minimum mass at which they can start fusion. The only other way it would hide is if its a brown dwarf (a cold dead star that emits no light), these are impossible to see, but again it would have to be far enough away that it has no obvious pull on the orbits of the planets (either in a highly eccentric orbit or a more spherical orbit far away). This would make it very weakly bound to our solar system if at all by gravity...so I would say very unlikely.

I would say the sun has a twin,and a very likeliness of a twin universe as well.This is studied by scientists and they believe it is not out of the realm of possibly.

Within our solar system, another sun, no. I think we would have noticed it by now.

It hides behind Jupiter every time we try to locate it. Sly devil of a twin, it is.

No there can't be a twin. Even if it were invisible. The centre of gravity of the Sun-Twin system would be half way between the two and both would move about this centre. The Sun would "wobble" about this centre the same way that distant planets are detected by the wobble of their sun. From our point of view, it would seem that the whole night sky was being moved in huge slow circles. Our instruments are good enough to accurately measure the veolcities of nearby stars - any periodic variation in all their motions would be detected.

By definition, a star must burn hydrogen through nuclear fusion. This reaction produces energy which causes said star to glow in the visible spectrum. If there wer another star gravitationally bound to the Sun, then it would be have to be close enough to us for us to be able to see it. It would also move fast enough that we would be able to detect its movement against the back ground of stars. There is no star close enough to us to be gravitationally bound to the Sun. This twin does not exist.

It isn't in our solar sytem. The solar system is what is orbiting around a common center of mass, with companion star(s), outside of our solar system. Forget millions of years. The so called 'precession' takes roughly 24,000 years. That is the orbital period. People will say it is impossible due to violating 'laws' about how far away this companion would have to be, however laws must conform to reality and observations, not the other way around. Do some investigating and thinking, and you will discover this FACT: If precession was caused by the Earth's wobble, there would be precession in relation to other objects INSIDE the solar system. Everything such as meteor showers, conjunction times, seasons, would all need to be adjusted for the rate of precession. They are not. The only thing we are precessing in relation to is outside of our solar system - the stars. In other words, the entire solar system is curving through local space, with a period of about 24,000 years. Any other arguments and propoganda are irrelevant. Also, the rate of precession is accelerating. And using data over the last 100 years for the rate of acceleration, along with Keplers theories, we probably reached apoapsis at about 500 AD.

In our solar system? Nah, we would definitely see it.

If there was another star anywhere near our solar system, we'd know about it. It's not like it can hide from us.