Open a new window with:
Width: 600pixels
Height: 600pixels
Resolution: 72 pixels/inch Mode:
RGB color Contents: White

 

Choose Gradient Tool (G) > Radial Gradient

Put your mouse on the center of the image and holding Shift make a gradient pull as shown to the left.

Make a new layer Shift+Ctrl+N (). Click D to make your Foreground and Background colors to Black and White. Now go to Filter > Render > Clouds and click OK.

This time apply Filter > Render > Difference Clouds and click OK. Click Ctrl+F to apply one more time Difference Clouds to the layer.

Now you should have an image like shown to the left.