Astronomers Say Star Passed Through Oort Cloud 70,000 Years Ago

Posted on February 17, 2015

Astronomers say a star passed through our solar system's Oort Cloud 70,000 years ago. The star, known as Scholz's star, has a brown dwarf companion. The pair is now 20 light years away. The star would have been 0.8 light-years (8 trillion kilometers or 5 trillion miles) from Earth during its flyby. This is five times closer than Proxima Centauri, the closest star to Earth.

The above image is an artist's conception of Scholz's star and its companion during its flyby of our solar system 70,000 years ago. Our Sun is the brilliant star on the left in the image. Scholz's star is named after astronomer Ralf-Dieter Scholz of the Leibniz-Institut für Astrophysik Potsdam (AIP) in Germany who discovered it in late 2013. It's formal name is WISE J072003.20-084651.2.

Eric Mamajek from the University of Rochester lead the team of astronomers that analyzed the velocity and trajectory of Scholz's star. The astronomers say they are 98% certain Scholz's star and its companion passed through the outer Oort Cloud, a region at the edge of the solar system that is filled with trillions of comets.

Mamajek says in a statement, "Most stars this nearby show much larger tangential motion. 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."

The astronomers determined the star's trajectory using its tangential velocity and the radial velocity. The spectrum and Doppler shift of the star were measured using spectographs from the Southern African Large Telescope (SALT) and the Magellan telescope at Las Campanas Observatory. The astronomers figured out how fast Scholz's star was moving away from our solar system and traced it back to its positions 70,000 years ago when it was the closest to our Sun.

A research paper on the star's flyby of our solar system can be found here in the journal, The Astrophysical Journal.



More from Science Space & Robots