A Star Came Within 0.8 Light-Years Of Our Sun 70,000 Years Ago

http://io9.com/a-star-came-within-0-8-light-years-of-our-sun-70-000-ye-1686500486




http://i.kinja-img.com/gawker-media/image/upload/s--TNUHn0TD--/c_fit,fl_progressive,q_80,w_636/bzrvjprog6ejaelcgrar.jpg
Artist's impression of the red dwarf Scholz's star and its brown dwarf companion. (Credit: Michael Osadciw/University of Rochester)

An international team of astronomers has identified a star that passed through the outer reaches of the Oort Cloud some 70,000 years ago. It came within a distance of 0.8 light-years, making it the closest known flyby of a star to the Solar System. The star, dubbed Scholz's star, is actually part of a binary system. Its companion is a brown dwarf, a kind of "failed star" reminiscent of a gas giant. After analyzing its current trajectory, a group of astronomers from the United States, Chile, Europe, and South Africa have calculated that at its closest approach, it came within approximately 52,000 AU to the Sun, or 0.8 light-years. That's 5 trillion miles (8 trillion km), which, by cosmological standards, is excruciatingly close for an interstellar flyby of this nature.

Not Quite Visible From Earth — But Just Maybe...

When it visited our Solar System, it flew through the outer reaches of the Oort Cloud — a massive spherical region comprised of trillions of bits of ice, rock, and planetesimals. The cloud's maximal distance is 0.8 light-years, which places it at one-fifth the distance to the nearest star, Proxima Centauri. The outer limit of the Oort cloud is considered the cosmographical boundary of the Solar System and the outermost limit of the Sun's dominant gravitational influence.

When Scholz's star was in the neighborhood, it would have been a 10th magnitude star (red dwarfs are very dim). That's about 50 times fainter than what can be seen with the naked eye at night. Under normal circumstances, it would be invisible. But because red dwarfs are magnetically active, it could have briefly "flared-up" (i.e., V-band flares) to become thousands of times brighter. The astronomers say it's possible that the star was visible to our paleolithic ancestors for a few minutes or hours if this rare flaring event transpired at the time.

Slow Tangential Motion

Scholz's star is now 20 light-years away, but it displays very little motion across the sky, or what astronomers refer to as slow tangential motion. To the scientists, this indicated one of two possibilities: either the star is moving directly towards us or it's moving away...