![]() When this happens, the star begins to blow a strong "wind" that clears away the residual material. Some astronomers believe that, left to its own devices, a star will continue to grow until it nears the point where nuclear fusion begins in its interior. This process is markedly different from the process that governs the sizes of stars forming in isolation. "We believe that the stars in M16 were continuing to grow as more and more gas fell onto them, right up until the moment that they were cut off from that surrounding material by photoevaporation," said Hester. Ultimately, photoevaporation inhibits the further growth of the embyronic stars by dispersing the cloud of gas they were "feeding" from. "As soon as the star in an EGG is exposed, the object looks something like an ice cream cone, with a newly uncovered star playing the role of the cherry on top." "In a few cases we can see the stars in the EGGs directly in the WFPC2 images," says Hester. The ultraviolet light from nearby stars does the digging for us, and we study what is unearthed." "In some ways it seems more like archaeology than astronomy. "This is the first time that we have actually seen the process of forming stars being uncovered by photoevaporation," Hester emphasized. Some EGGs have pinched off completely from the larger column from which they emerged, and now look like teardrops in space.īy stringing together these pictures of EGGs caught at different stages of being uncovered, Hester and his colleagues from the Wide Field and Planetary Camera Investigation Definition Team are getting an unprecedented look at what stars and their surroundings look like before they are truly stars. (The fingers are gas that has been protected from photoevaporation by the shadows of the EGGs). Others have been uncovered more completely, and now resemble "fingers" of gas protruding from the larger cloud. Some EGGs appear as nothing but tiny bumps on the surface of the columns. But in M16, instead of rocks, the ultraviolet light is uncovering the denser egg-like globules of gas that surround stars that were forming inside the gigantic gas columns." "As the wind blows away the lighter sand, heavier rocks buried in the sand are uncovered. "It's a bit like a wind storm in the desert," said Hester. The EGGs, which are denser than their surroundings, are left behind after the gas around them is gone. But not all of the gas boils off at the same rate. "The Hubble pictures show photoevaporating gas as ghostly streamers flowing away from the columns. Hubble gives a clear look at what happens as a torrent of ultraviolet light from nearby young, hot stars heats the gas along the surface of the pillars, "boiling it away" into interstellar space – a process called "photoevaporation. Inside the gaseous towers, which are light-years long, the interstellar gas is dense enough to collapse under its own weight, forming young stars that continue to grow as they accumulate more and more mass from their surroundings. The columns – dubbed "elephant trunks" – protrude from the wall of a vast cloud of molecular hydrogen, like stalagmites rising above the floor of a cavern. Striking pictures taken by Hester and co-investigators with Hubble's Wide Field and Planetary Camera 2 (WFPC2) resolve the EGGs at the tip of finger-like features protruding from monstrous columns of cold gas and dust in the Eagle nebula (also called M16 – 16th object in the Messier catalog). "Now in M16 we seem to be watching at least one such process at work right in front of our eyes." "For a long time astronomers have speculated about what processes control the sizes of stars – about why stars are the sizes that they are," said Jeff Hester of Arizona State University, Tempe, AZ. Hubble found the "EGGs," appropriately enough, in the Eagle nebula, a nearby star-forming region 6,500 light- years away in the constellation Serpens. Four Successful Women Behind the Hubble Space Telescope's AchievementsĮerie, dramatic new pictures from NASA's Hubble Space Telescope show newborn stars emerging from "eggs" – not the barnyard variety – but rather dense, compact pockets of interstellar gas called evaporating gaseous globules (EGGs).Characterizing Planets Around Other Stars.Measuring the Universe's Expansion Rate. ![]()
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