I always thought that p-orbitals had a dumbbell shape as pictured below.

[![enter image description here][1]][1]

([image source][2])

However, I was reading an [article][3] (see Table 1, item 2) that says, "...the spherical $\mathrm{p_{1/2}}$ subshell...". Why do they call the p orbital spherical?


  [1]: https://i.sstatic.net/8djtR.jpg
  [2]: https://socratic.org/questions/how-do-you-draw-spdf-orbitals
  [3]: http://www.sciencedirect.com/science/article/pii/S129325580500230X