Today, the closest star to our solar system is Proxima Centauri – about 4.2 light years away from our sun. But, this wasn’t always the case. 70,000 years ago, another star was closer.
Nicknamed ‘Scholz’s star,’ this star’s trajectory points to it being within 1 light year (0.8 light years to be exact) around 70,000 years ago. In a paper, the team of astronomers are nearly certain the star passed through the “outer Oort cloud.” The Oort cloud is a region at the edge of our solar system filled with countless comets.
The star caught the attention lead author Eric Mamajek (University of Rochester) and his fellow astronomers because of its unusual characteristics. One of these was its very slow tangential motion, or motion across the sky. Radial velocity measurements showed the star moving directly away from our solar system at a decent speed.
“Most stars this nearby show much larger tangential motion,” Mamajek said. “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 team of astronomers used the South African Large Telescope and the Magellan telescope at Las Campanas Observatory to figure out its tangential motion and radial velocity. With these two measurements they were able to figure out Scholz’s star was indeed moving away from the Sun and used models to trace back its closest position to the Sun.
To get the 98% figure, Mamajek worked with Scott Barenfeld, a former University of Rochester undergraduate, to simulate 10,000 orbits of Scholz’s star. 98% of these simulations brought the star into the outer Oort cloud. One of them even brought the star into the inner Oort cloud.
Did our ancient ancestors see the star? Maybe. Scholz’s star is a small, dim red dwarf. When it was less than a light year away Earth it would have appeared as a 10th magnitude star. Way too dim to see with the naked eye. But, the star is magnetically active. Flare-ups could have caused the star to brighten enough to see it at night. These rare flare-ups would have lasted for minutes, maybe an hour.
How about other stars? The European Space Agency recently launched the Gaia satellite. Gaia is expected to map distances and velocities of a billion stars. Armed with this data, astronomers will be able to pinpoint stars that may come near us in the future.