Thursday, February 26, 2015

Small Star Passed By Edge of Solar System 70,000 Years Ago

By Ron Cowen and Nature magazine

A recently discovered stellar neighbour of the Sun penetrated the extreme fringes of the Solar System—the closest encounter ever documented—at around the time that modern humans began spreading from Africa into Eurasia.

The red dwarf star, which has a mass about 8% that of the Sun and is orbited by a 'brown dwarf' companion—a body with too little heft to sustain the thermonuclear reactions that enable stars to shine—was discovered in 2013 in images recorded by NASA’s Wide-field Infrared Survey Explorer (WISE) mission. It is relatively nearby, at about 6 parsecs (19.6 light years) away.

Astronomer Eric Mamajek at the University of Rochester in New York became intrigued by it when he learned that the faint object is moving slowly across the sky, but its radial velocity—the rate at which it is moving away from an observer—is high. That indicated that the low-mass star, nicknamed Scholz’s star after the German astronomer who discovered it, is racing almost directly away from the Solar System.

Tracing the trajectory of the star and its brown dwarf companion back in time, Mamajek’s team found with 98% confidence that Scholz’s star passed within the Solar System's Oort cloud, a reservoir of comets, about 70,000 years ago.

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Sources: Nature Magazine, Scientific American Magazine.

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