Nikon Astrophotography?

Pentax has an 'astrotracer' for start tracking, does Nikon have a similar camera accessory?

The Nikon camera designed specifically for astrophotography is the Nikon D810a

Here is a link to that camera.

You are still going to have to mount it on a computer controlled telescope to take the necessary long exposures when photographing deep space.

The "astrotracer" is really a unique GPS/tracking tool used to keep the camera aimed at the correct portion of space where you are interested in photographing. At this time, there are no Pentax cameras that have a special sensor made specifically for shooting deep space.

Astrotrac has a generic product that can be used by an DSLR.
http://astrotrac.com/products/astrotrac-tt320x-ag.html

I'll bet they make the 'astrotracer' for Pentax.

No, Nikon does not. But there are 3rd-party hardware solutions that will track the movement of the stars for you to avoid star trails.