Hello,
I can't speak for that picture, but almost all stars are too far away to see a disk of. The only exceptions I can think of are the Sun and Betelgeuse (I'm pretty sure there's another, but I can't remember it). The reason you get that "blob of light" is because of a property of the film (or the CCD chip if it's a digital image). Light "spills over" onto the surrounding area, making it look like that. One way to see this is to take successive pictures of a star (this will work if you can track the star) at different time intervals (30 seconds, 1 minute, 1.5 min, etc...). You'll notice that the shorter exposures will show smaller dots.
I hope this information helps.

Phil
The Edge of Nowhere...
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