Proxima Centauri!!! And the Planet X puzzle is SOLVED. (oooo...watch em come out of the woodwork now...! )
Oh, here is a link if you want to figure it out for yourself. (I did the math: 1 LY=5,865,696,000,000 miles x 4.2 =24,635,923,200,000 miles away; 16,000 miles per second = 504,576,000,000 miles per year that our sun and Proxima Centauri are traveling towards each other, which means that from the point that the calculation was made they should reach each other in 48.25 years.