Closest star flyby of the solar system occurred 70,000 years ago

A group of astronomers from the US, Europe, South Africa, and Chile have determined that, approximately 70,000 years ago, a recently discovered star is likely to have passed through the Oort Cloud, a region at the edge of the solar system from which comets arise (1). Its average distance at the time was five times closer than that of the current closest star, Proxima Centauri.

Star Flyby

Images of a red dwarf star, the type of star that was involved in the flyby.
Source: Wikimedia Commons

Eric Mamjek of the University of Rochester and his team analyzed the velocity and trajectory of what was nicknamed “Scholz’s star.” The low-mass star’s trajectory suggests that, 70,000 years ago, it passed as close as 0.8 light years (5 trillion miles), away. In astronomical terms, this is very close; our current closest star, Proxima Centauri, is 4.2 light years away. The researchers are 98% certain that Scholz’s star passed through the outer Oort Cloud (2).

Scholz’s star has an unusual mix of characteristics. Its current distance from the solar system is 20 light years, but it shows very slow tangential motion, or motion across the sky. Mamjek explains that “most stars this nearby shows much larger tangential motion” and notes that the star’s small tangential motion and proximity indicate that it is most likely moving towards a future encounter with the solar system, or moving away from one (1).

When the astronomers worked out the star’s radial velocity, the measurements were consistent with it moving away from the Sun’s vicinity. The team then traced the star’s position back in time 70,000 years, when their models indicated it came closest to the Sun.

Currently, Scholz’s star is a small, dim red dwarf about 20 light years away. At its closest flyby of the solar system, it would have been 50 times fainter than what the naked eye can normally see at night. However, its magnetic “flares” can cause it to become briefly thousands of times brighter, allowing it to be observed. It is possible that human ancestors may have seen the star on these brief occasions.

Sources:

1. University of Rochester (17 Feb 2015) Closest known flyby of star to our solar system: Dim star passed through Oort Cloud 70,000 years ago. ScienceDaily. Retrieved February 21, 2015 from www.sciencedaily.com/releases/2015/02/150217114121.htm

2. Mamajek EE, et al. (12 Feb 2015) The Closest Known Flyby of a Star to the Solar System. The Astrophysical Journal, 800. doi: 10.1088/2041-8205/800/1/L17

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