A few months back I got into a discussion about the possibility of finding our Sun’s long lost siblings. What a family reunion that would be! But let’s back up a bit first and look at the basics of the story. Our Sun and it’s planets formed in a vast cloud of gas and dust some 4.56 billion years ago. This cloud had been around for millions of years, the remains of huge supernova explosions from ancient, long dead stars. Something disturbed this cloud, a nearby supernova perhaps, and the shockwave or pressure wave, caused areas in the cloud to clump together. This in turn meant that the increased density of these clumps increased the strength of their gravity and they started to contract. This would have happened in hundreds or possibly thousands of areas throughout the nebula and eventually there would have been countless new stars and planetary systems forming.
So this is the beginning of our story. Our Sun is one of hundreds or thousands of new stars, born in the same stellar nursery so it should be easy to find the others, shouldn’t it? Well actually it’s not, because these new stars, although relatively close to each other, are all orbiting the centre of our galaxy, all with a slightly different velocity. This would only be a very small difference, but over 4.6 billion years and close(ish) encounters with other stars along the way, these stellar siblings have wandered off and got separated. So how do we find them? Can we find them?
Well we can start with some basic, logical, assumptions. Firstly, being formed in the same nebula, they will have a similar composition. Secondly, although they have wandered off in different directions, some may have retained a somewhat similar path around the galactic centre. And thirdly, we can trace the paths of stars and extrapolate back to the start. The first is fairly easy, spectography tells us what a star is made of so we just have to find those with a similar composition to the Sun.
Number 2 is a bit iffy. Just because we observe a star with a similar velocity to us, doesn’t mean it always has done so this is no more than an indicator that a star might be worth considering. Number 3 is where it gets a bit complicated but is still “doable”. We follow a star thorough the sky and plot it’s path relative, not to us, but to the centre of the Galaxy. We can then try to wind the clock back, tracing the star’s path over the 4.6 billion years the Solar System has existed. and see if they end up/start out in the same place. The Solar System orbits the Galactic centre once every 225- 250 million years so the Sun has been around the Galaxy about 20 times since it formed and a lot can happen on that long journey so this can never be 100% but not far off.
So, can it be done? Well yes it can and it has been. A team at the University of Texas has done just that, and by analyzing the orbits and chemical compositions of 23 candidate stars, they have narrowed it down to one star, (so far), HD 162826. It’s about 15% bigger than The Sun and lies in the constellation of Hercules at a distance of 110 light years from our Solar System.
Ok, we won’t be popping by to visit the family just yet, but this discovery opens up some intriguing possibilities, that HD 162826 probably has planets, possibly an Earth like planet and who knows, maybe life. So maybe one day we might meet our own long lost siblings, and HD 162826 is only the first of hundreds or possibly thousands of our Suns siblings waiting to be (re)discovered!
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