Its 4.5 billion years since our solar system formed in a gaseous nebula. These nebula formed from the explosive collapse of stars, larger than Sol, when they have exhausted much of their hydrogen. These Supernova cast much of their mass into space forming a gaseous nebula. These nebula are however large – much larger than our solar system and are incubators of star formation, sometimes hundreds of stars, much like the glowing nebula in the image below.
Overtime, the varied gravitational environment in the galaxy results in stars formed from the same nebula drifting apart, however they will retain the same composition and have similar spectral characteristics and maybe even be of comparable in size. Finding these siblings would require a massive star survey. We would have to know the distance from Earth, the relative speed and direction and the composition. Given that there are a vast number of stars in our immediate neighborhood – this is a daunting task.
The Gaia spacecraft is performing just such a survey of the Milky Way. Gaia is measuring the distance, velocity and spectral characteristics for a billion stars in our galaxy has now spotted what appears to be a twin (HD186302) of Sol and it has near identical spectral characteristics. Of the 200,000 stars in the spectral Gaia catalog only one star, HD186302, has near-identical chemistry to Sol.
HD186302 is a G3-Type main sequence star with about same surface temperature as Sol and is about the same age, 4.5 BY. HD186302 is located 184 light years from Earth, which sounds like it’s very distant. However, to achieve this separation if Sol and HB186302 were original 1-2 light-years apart within the nebula it would only require a relative velocity between Sol and HD186302 of 65,000 km/hr since formation to have achieved the current separation. In galactic terms this is a very realistic relative speed.