how could we find out (or rule out) that the solar system is a former binary-star system ?
just found that interesting to ask, cause of a new NASA release about multiple star systems detected with the spitzer-telescope
http://www.nasa.gov/mission_pages/spitzer/news/spitzer-20070724.html
jimschem
Favorite Answer
Statistically, most stars form in groups or clusters.
Our sun's closest stellar neighbor is actually a group of 3 stars.
http://www.solstation.com/stars/alp-cent3.htm
Suppose our Sun formed with a second star like itself.
Let's say they orbited each other separated by 4 billion miles
with a period of 1,000 years.
You would be forced to answer the question - what caused the second star to leave?
The run away star should be receding from us by about 12 million miles a year or 1 light year every 500,000 years
Even if it left 5 billion years ago (the known age of the Sun)
it could only have only gotten 10 light years distance and be easily observed.
It would also have no apparent motion (i.e. no up or down or left or right motion) just motion away from us. Its spectral light would be red shifted.
At 10 LY or less it would still be in our stellar neighborhood.
I don't believe any star matching that description has been observed.
If it went nova or supernova there would be a ring or planetary nebula moving away from us in our neighborhood.
The most likely scenario is that our Sun formed as a lone star.
minuteblue
We've known about multi-star systems for a while and the speculation that our own solar system is/was binary has been around for a while.
How would we know our solar system used to consist of two or more close proximity stars when it was very young? I'm not sure. No doubt it would have been a very long time ago and we'd have to find some evidence that our current sun is either the result of a collision of smaller stars or that another star got flung out of the system never to be seen again, or was it?
There may be motions of our sun and solar that can be detected that implies that it is gravitationally locked with another star. This star would be dim and difficult to spot in the vastness of space. It may have a highly elliptical orbit which only brings it "near" our own sun every few million years and "near" still means very far.
Jupiter was never a candidate to become a star. It would need at least 80 times more mass to sustain nuclear fusion.
Anonymous
This NASA site gives a possibility of stellar systems with both planets and stars. But our Solar system is simple: only one star. Yes? Well, our system may be considered double as the mass center between Jupiter and the Sun falls outside the Sun. Although Jupiter don't radiate light, but radiate more energy (as IR) that the received by the Sun. Ganymede (Jupiter satellite) is larger than Mercury. So our system is not so far from a real double system.
If the question is about a long-time-ago real double system, Sun-Jupiter, I don't believe that. The smallest is a star, the longest is its life to be radiating light, so Jupiter is a big (quasi star) planet, but not a died star.
If the question is about a former system double or multiple, that was destroyed, how this system become simpler? Why the planets have almost circular orbits? The circular orbits look a result of a simple system.
Justin D
I am not sure. My first guess has to do with the most commonly accepted theory about the origins of our solar system. Basically, a solar system starts out as a collection of dust and gases. The gases and dust coallesce into progressively larger balls according to a feedback cycle: the larger the dust and gas ball, the more dust and gas it can collect. It is like a snowball effect. In order to become a star that has the capacity for fusion, a ball of dust and gas must reach a certain size. If our solar system had another star, It is difficult to see what could have happened to a body of that size. Perhaps it could have escaped the gravity of the solar system and gone its separate way. It does not seem likely though, but I guess it can not be ruled out.
dgreatunknown
I don't think there is any evidence that our solar system was ever binary. There are different types of star systems with two or even more stars, but others, like our own, has only one sun.
There is a very slight chance that another star can come close enough to our sun that it will start orbiting us (or we to it)