The Elephant’s Trunk nebula, formally known as IC1396A, is a cloud of gas and dust located 2400 light years from Earth in the constellation Cepheus. The Elephant Trunk is part of a larger region of ionized gas illuminated by a nearby massive O-type star (located outside the image to the left). Radiation and winds from this hot star compress and ionize the edges of cloud, resulting in the bright “ionization fronts” seen in this image.
Young stars at very different stages of formation have been found both within and just outside the Elephant’s Trunk. Very young protostars, still accreting material from the surrounding nebula, are located inside the cloud, while fully formed stars have been found just in front of the ionization edges. This suggests that star formation has been proceeding sequentially through the cloud as a result of the ‘triggering’ effects of the hot star (Barentsen, 2011). On the order of 5% of the mass of gas and dust in the cloud has already been turned into protostars (Reach, 2004), and the process is continuing today.
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Image credit: Nick Wright (University of Hertfordshire, SAO), Geert Barentsen (University of Hertfordshire, Armagh Observatory