A group of astronomers from the US, Europe, Chile and South Africa has identified the closest known flyby of a star that passed our solar system at a distance of mere 0.8 light years 70,000 years ago.
The dim star is likely to have passed through the solar system’s distant cloud of comets – the Oort Cloud.
No other star is known to have ever approached our solar system this close – five times closer than the current closest star known as Proxima Centauri.
Lead author Eric Mamajek from the University of Rochester in New York and his collaborators analysed the velocity and trajectory of a low-mass star system nicknamed "Scholz’s star."
The star’s trajectory suggests that 70,000 years ago, it passed roughly 52,000 astronomical units away (or about 0.8 light years).
This is astronomically close; our closest neighbour star Proxima Centauri is 4.2 light years distant.
"We are 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," the authors wrote.
While the close flyby of Scholz’s star likely had little impact on the Oort Cloud, Mamajek points out that "other dynamically important Oort Cloud perturbers may be lurking among nearby stars."
The recently-launched European Space Agency Gaia satellite is expected to map out the distances and measure the velocities of a billion stars.
With the Gaia data, astronomers will be able to tell which other stars may have had a close encounter with us in the past or will in the distant future.
Currently, Scholz’s star is a small, dim red dwarf in the constellation of Monoceros, about 20 light years away.
The paper was published in Astrophysical Journal Letters.