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Elephant trunks
Elephant trunks are formations of interstellar matter found in space. More formally, scientists sometimes refer to them as 'cold molecular pillars',〔(【引用サイトリンク】first=G.F. )〕 referring to their existence in molecular clouds. They are located in the neighborhood of massive O type and B type stars, which, through their intense radiation, can create expanding regions of ionized gas known as H II regions. Elephant trunks look like massive pillars or columns of gas and dust, but they come in various shapes, lengths, and colors. Astronomers study elephant trunks because of their unique formation process and use 2D and 3D simulations to try to understand how this phenomenon occurs.
== Formation ==
O type and B type stars are a classification of stars that strongly emit ultraviolet (UV) radiation. The UV radiation causes the surrounding cloud of hydrogen gas to ionize, forming H II regions.〔(【引用サイトリンク】first=Carl )〕 The gas does not ionize evenly throughout the cloud, therefore there are randomly generated clumps of denser gas scattered throughout the cloud. These dense clumps are called evaporating gaseous globules (EGGs), and they are the starting point for the formation of an elephant trunk. The pillar shape is formed when the EGGs act as a shield for the gases that lay behind them from the stellar winds.〔(【引用サイトリンク】first=W. )〕 Stellar winds are a continuous flow of gas that is ejected from the stars and causes the lighter and less dense gas to erode away.〔(【引用サイトリンク】first=Chris )〕 The EGGs and the column of gas "downwind" from them is the basic formation of an elephant trunk.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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