Astronomers identify the closest known flyby of a star

About 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, say astronomers from the U.S., Europe, Chile, and South Africa. 
The Sun seen to the left in the background, would have appeared as a brilliant star. The pair is now about 20 light-years away. No other star is known to have ever approached our solar system this close — five times closer than the current closest star, Proxima Centauri. Eric Mamajek from the University of Rochester in New York and his collaborators analyzed 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, which equals 5 trillion miles [8 trillion kilometers]). This is astronomically close; our closest neighbor star Proxima Centauri is 4.2 light-years distant. In fact, the astronomers explained 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-period comets orbiting the Sun after their orbits are perturbed.

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