These are [diffraction spikes][1]. They are an interference pattern caused by the the arms of the telescope. [![Webb][2]][2]

The six spikes are these three arms and the inverted image of those 3 arms. 

You can think of them as a type of "shadow" the telescope is casting. They occur around whatever is bright enough in the image which in this case is all the stars that are within the milky way.  These stars show up super bright because the webb is trying to look for super dim objects in the deep field. 


  [1]: https://www.wikipedia.org/wiki/Diffraction_spike
  [2]: https://i.sstatic.net/dvqy5.jpg