Re: Is our sun binary?

This is a very interesting question, Sara. While it seems to be a simple question, it isn't (as none I have recieved so far are).To draw an answer from this, we need no telescopes, but logic. The better we understand a concept, the more we can learn.

First lets talk about the three types of binary star systems. The first is where two stars of equal mass cirle around a central point. The second is where one star is much more massive thant the other, both circling a center point, but the larger's orbit being far closer. The third is actually a double-binary system, imagine the first system described but there are four stars; two pairs cirling a point, and each of those points cirling another point. Stay with me, this is a little odd.

Ok, now let's talk about our own sun. There is nothing unusual about it, it is average size and average age. It burns hydrogen, has sunspots, and makes things warm here on Earth. Now, is this sun a candidate for a binary star system?

If we look at the first system we can say definitely yes. But is it? No. If it was, we'd have some unpleasant effects from its sister star. Now, this sun would have to be relatively close. That means heat, and lots of it. At least close to the amount we already get from our own sun. It also means solar wind, which would throw our whole global electromagnetism out of whack, and instead of our own field being blown away from the sun, it would instead go all over the place from our changing position relative to these two suns. Also, we would absolutely see it- no question about that one. So, we cant see it, we arent fried, it isnt part of one of those systems.

Is it part of the second? Well, with my credible but not vast knowledge of astronomy I can say almost definitely no. We would not be the larger one, but the smaller one. If the situation was right and we were circling a very, very massive star that was very, very far away, we would have trouble detecting that. But that variation of the binary system we are discussing is rare, so it is unlikely we are part of one of those.

It should be obvious we are not part of one of the last, because that would mean we are part also of one of the first systems we discussed, which I stated we are not.

Thanks for the question, I hope this clears everything up for you.

[Moderator's Note:

Max is right, there is very little evidence that our Sun is part of a binary system, although something like 50% of the stars in our galaxy are in binary or triple systems.

You might find this discussion of the Nemesis theory interesting. It also has references to other discussions of this question.

Jim O'Donnell, MadSci Admin]