If this appeared here earlier I missed it.
The nearest star system to ours is Alpha Centauri (A, B and Proxima). Everybody know that.
The second nearest is Barnard’s star, the star with the fastest motion across the sky.
The third nearest … was discovered March 2013 !!
And is already known to be a double star system.
A news article about the discovery is
http://science.psu.edu/news-and-events/2013-news/Luhman3-2013
The discovery paper is
Luhman, K. L. (2013). “Discovery of a Binary Brown Dwarf at 2 Parsecs from the Sun”. http://arxiv.org/pdf/1303.2401.pdf
The wikipedia article is:
http://en.wikipedia.org/wiki/WISE_1049-5319
Interestingly, this new star system is closer to Alpha Centauri than the Earth is. Both stars in the system are brown dwarfs, the brightest is of type L7.5 and the other component is of type T0.5, or to put it another way, are not greatly hotter than a young planet.
“With a distance of 2.0±0.15 pc, WISE 1049−5319 is the closest neighbour of the Sun that has been found in nearly a century. It is only slightly more distant than Barnard’s star, which is the second nearest known system (1.834±0.001 pc) and is closer than Wolf 359. The low galactic latitude is likely the reason why it was not found in previous surveys
for nearby brown dwarfs, which have tended to avoid the galactic plane. Because of its proximity to the Sun, WISE 1049−5319 is a unique target for a variety of studies, such as direct imaging and radial velocity searches for planets.”
Being so near makes it very very interesting.
Data from the WISE satellite collected in 2010 has now been used to find the 3rd nearest, 10th nearest, 14th nearest, 36th nearest and 49th nearest star systems to us.