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Hubble Captures Eye-like Space Oddity
By Maia Weinstock
Staff Writer
posted: 12:55 pm ET
06 April 2000
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Hubble Captures Eye-like Galactic Weirdo Astronomers using the Hubble Space Telescope recently released a striking new image of a planetary nebula, or dying star, called NGC 6751 in the constellation Aquila. Resembling a glowing eye, the nebula was found to be 6,500 light-years away from Earth in a far region of the Milky Way galaxy. Its discovery is helping astronomers map stars in our home galaxy and understand the eventual fate of our own sun. Planetary nebulas are big, bright clouds of gas and dust that puff out from an exploding, dying sun. They are so named not because they have anything to do with planets, but because of their round shape. Astronomers are learning a great deal about planetary nebulas at the edge of our galaxy and beyond. But interestingly, they lack some important data about nebulas in our own Milky Way. "The sad fact is, we know distances to planetary nebulae in other galaxies better than we know distances to planetary nebulae in our own galaxy," said Arsen Hajian, an astronomer at the U.S. Naval Observatory. Hajian decided to remedy this problem by measuring the distances to 30 stellar objects viewed through the Hubble Space Telescope. To do this Hajian took pictures several years apart of the same objects, including NGC 6751 (pictured below). Comparing before and after images of the same object gives astronomers a good idea of the angle and velocity at which the nebula is expanding. Then knowing these two factors, astronomers can calculate a distance to the object from Earth. 
NGC 6751 is apparently an odd planetary nebula because it resembles another type of solar explosion called a supernova. "NGC 6751 is a real weirdo," said Hajian. "Most other [planetary nebulas] look like theyve got pretty, smooth-looking shells. 6751 looks like somebody ripped it apart into little pieces." Experts arent sure why exactly this particular planetary nebula looks so odd compared to other planetary nebulas. One possibility, said Hajian, is that NGC 6751 is interacting with gas shreds in the interstellar medium surrounding the nebula, thus causing it to "puff out." Astronomers expect that our own sun will someday end up as a similar planetary nebula after it dies. However, because our sun has large gaseous planets like Jupiter and Saturn surrounding it, it might look more like an elliptical egg than a circular eye when it does explode. "The current theory is that if youve got a planet in your solar system, and that star dies, itll turn into an elliptical planetary nebula," explained Hajian. "Its possible that [NGC 6751] is an explosion very much like our sun, but it might not have any planets around it."
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