It is believed that most of the star formation in the Seagull Nebula region were induced by the explosion of a supernova. Several clues support this hypothesis:

The semicircle shape on the right (south) side of the image forms two sides of an open cavity with a diameter of about 3 degrees;

the absence of bright stars within this bubble;

and finally, the evidence of the expansion of the bubble itself, composed of neutral hydrogen and observable in the maps drawn at this wavelength, very clear in the color image below.