A close call of 8 trillion kilometres
The star, nicknamed “Sholz’s star,” is believed to have passed roughly 0.8 light years away, which is equivalent 8 trillion kilometres or 5 trillion miles from our sun. This is the nearest any star other than our sun has been to our solar system, and is five times closer than the current closest star Proxima Centuari, which lies 4.2 light years away.
Currently, Scholz's star is a small, dim red dwarf in the constellation of Monoceros, about 20 light years away.
In the paper, published in The Astrophyiscal Journal Letters, Mamajek describes how the team made this discovery.
"Most stars this nearby show much larger tangential motion (that is, motion across the sky)" He explains, "The small tangential motion and proximity initially indicated that the star was most likely either moving towards a future close encounter with the solar system, or it had 'recently' come close to the solar system and was moving away.
Sure enough, the radial velocity measurements were consistent with it running away from the Sun's vicinity - and we realized it must have had a close flyby in the past."