Recently identified dim star passed very close to our solar system 70,000 years ago

Washington: A team of astronomers has identified the closest known flyby of a star to our solar system.

Astronomers from the US, Europe, Chile and South Africa have determined that 70,000 years ago a recently discovered dim star is likely to have passed through the solar system's distant cloud of comets, the Oort Cloud.

The star's trajectory suggests that 70,000 years ago it passed roughly 52,000 astronomical units away (or about 0.8 light years, which equals 8 trillion kilometers, or 5 trillion miles). This is astronomically close and our closest neighbor star Proxima Centauri is 4.2 light years distant.

In fact, the astronomers explain in the paper that they are 98 percent certain that it went through what is known as the "outer Oort Cloud," a region at the edge of the solar system filled with trillions of comets a mile or more across that are thought to give rise to long-term comets orbiting the Sun after their orbits are perturbed.

Lead author Eric Mamajek from the University of Rochester said that most stars this nearby show much larger tangential motion and 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.

Mamajek added that sure enough, the radial velocity measurements were consistent with it running away from the Sun's vicinity and they 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 study is published in Astrophysical Journal Letters.