The Closest Star to Flyby the Solar System
Title: The Closest Known Flyby of a Star to the Solar System
Authors: E. E. Mamajek, S. A. Barenfeld, V. D. Ivanov, A. Y. Kniazev, P. Vaisanen, Y. Beletsky, H. M. J. Boffin
Long-period comets originate from the Oort cloud, but how do they come to travel into the planetary system? One hypothesis favors the existence of a companion to the Sun, but analysis shows that such a companion would be inconsistent with the observed periodic variations in long-period comets. It has also been proposed that stars pass near enough to the Oort cloud to alter the orbits of the comets towards the Sun.
A recently discovered star, WISE J072003.20-084651.2, also know as Scholz’s star or W0720, is about 23 light years away, near the Galactic Plane in the constellation Monoceros. The motion of the star makes it likely that it may have interacted with the Sun, or could in the future.
Scholz’s star is a binary system with a mass about 0.15 times the mass of the Sun and a stellar classification of M9.5+T5. The primary star (W0720A) is a red dwarf (M9.5) with a mass about 86 times the mass of Jupiter. The secondary (W0720B) is a brown dwarf (T5) with a mass about 65 times the mass of Jupiter. The velocity of Scholz’s star is similar to the large group of stars that make up the Hercules stream. The stream contains stars of different ages and compositions and by looking at stars with similar characteristics, it was determined that Scholz’s star is 3 to 10 billion years old.
The authors simulated 10,000 orbits of Scholz’s star and the Sun and saw that the closest pass to the Sun was 70,000 years ago at a distance of 0.8 light years, within the inner Oort cloud. For reference, the neighboring star Proxima Centauri is 4.24 light years away. In addition, 98% of the simulations resulted in a trajectory where Scholz’s star passed within the outer Oort cloud at a distance of 1.9 light years.
By comparing their results with other stars recently studied, the authors determined that Scholz’s star is the closest known star to flyby our system. At its closest approach of 0.8 light years, Scholz’s star would appear brighter than Proxima Centauri, but dimmer than naked eye stars. Scholz’s star is active, meaning that it experiences stellar flares. During a flare event, it is possible for Scholz’s star to be visible to the naked eye for a short period of time.
Further astrometry observations of Scholz’s star will provide more precise measurements about the star and the flyby.
Image: View containing Scholz’s star, circled in red. (Credit: WISE)