Welcome to Photoshop Gurus forum. Register a free account today to become a member! It's completely free. Once signed in, you'll enjoy an ad-free experience and be able to participate on this site by adding your own topics and posts, as well as connect with other members through your own private inbox!
It's just brush work. Play around with a very soft edged brush, and I'm sure you will get very close.
If you are particularly interested in reproducing the banding that is especially visible around the brightest blob, just apply PS's "Posterize" tool to your brush work.
Tom M
PS - you posted your second message while I was typing. I now see that you probably are not interested in the banding effect, so you can just ignore my second sentence.
oh sorry i think i missread i thoth that the second image on your post was your goal XD.
My inglish is not so good, but in the second image you use the first image to ilustrate the effect no?