Merging Stars 
While our Sun travels through space alone, many stars have one or more companions. Alpha Centauri, our closest neighboring star system, consists of three stars. And Sirius, the brightest star in all the night sky, consists of two stars.
A recent study of young star clusters suggests that many single stars started as double stars that merged during the first million years of their lives.
This study modeled a newborn star cluster filled with leftover gas and dust from the birth of the stars. In this simulation, the double stars had orbital periods that matched what astronomers observe when they study real newborn double star systems.
But over time, the model found that many of the pairs that were born close together interacted with the cluster’s remaining gas and dust. That produced friction that caused the stars to spiral together and merge to form a single star. As a result, the star cluster ended up with fewer close-together binaries — which is exactly what astronomers observe when they look at older stars. Indeed, stars in the most common binaries are so far apart that they take about 200 years to orbit each other.
Could our Sun have been born as two separate stars that then merged into one? It’s possible, but the researchers say it’s unlikely. Small planets like Earth and Mars may not have been able to take shape around a close binary. So the fact that we’re here suggests that the Sun isn’t just alone today — it was born that way.
Script by Ken Croswell, Copyright 2013