Select again the Ellipse Tool (U) to draw a kind of illuminating small circle of white color.

Blending Options-Outer Glow

Blending Options-Inner Glow

Make fifty copies of the new layer and apply the Free Transform option to change the copies’ size if necessary. Don’t forget to place them the way it is shown below:

Take a brush now of small size and white color and try to draw a lot of small points the way it is indicated below:

Applying the Pen Tool (P) now, try to represent the rest of the volume’s elements:

(White color)