astrophotography - Are hot pixels just one pixel?

I have been taking a few astro photos on a very high ISO, and have found what I think to be a few hot pixel. I though at first that I had managed to get a few very sharp pic of some red and blue stars. But now I have tried doing some stacking It seems that they are static to the rest of the moving sideways.

The thing that may have thrown me is that I thought that a 'hot pixel' was just that. A pixel, but it also seems to bleed outwards to make a small circle of a few faded pixels either side. Here is what I mean:

http://s3.amazonaws.com/twitpic/photos/full/263787358.jpg?AWSAccessKeyId=AKIAJF3XCCKACR3QDMOA&Expires=1301049641&Signature=xgTHJpe7s%2F36h5vGrDKKBmNeIZU%3D

The image was saved as 'fine' quality on a D90 on a 2500mm telescope (1250mm with 2x teleconverter).

So are these hot pixels?

Answer

A hot pixel is actually one or more hot photo sensors. Most camera sensor chips are made up of red, green and blue photo sensors, usually placed in a pattern similar to this:

RGRGRGRGRG
GBGBGBGBGB
RGRGRGRGRG

GBGBGBGBGB

Each of these photo sensors ends up as a pixel in the final image, but as each photo sensor only has information about one color component, information is used from the surrounding sensors. That is why a single hot photo sensor bleeds into several pixels.