Researchers identified the closest encounter our solar system has ever had with an outside star.
A team of scientists determined that about 70,000 years ago a dim star passed through the Oort cloud, which is closer than any other star is known to have come to our planet, the University of Rochester reported.
The recently-discovered object, dubbed "Scholz's star," would have been only about 0.8 light years (five trillion miles) away. Our current closest neighboring star, Proxima Centauri, is about 4.2 light-years away. The researchers say they are 98 percent certain the star passed though the outer Oort cloud, a region in the outer reaches of our solar system that is believed to give rise to comets that orbit the Sun.
The researchers observed Scholz's star was only 20 light-years away and moved very slowly across the sky. Radial velocity measurements revealed the star was actually moving directly away from our solar system at a surprisingly high speed.
"Most stars this nearby show much larger tangential motion," said lead author Eric Mamajek from the University of Rochester. "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."
To determine the star's trajectory the researchers looked at both its tangential velocity and radial velocity using spectrographs on large telescopes in both South Africa and Chile. When traced backwards, the measurements revealed the star's position 70,000 years ago. The star is now about 20 light-years away in the constellation of Monoceros. It is part of a binary star system containing a brown dwarf companion.
The findings were reported in a recent edition of the Astrophysical Journal Letters.
