Photos from NASA Hubble Space Telescope shows the beautiful Stingray nebula fading at an unprecedented rate.
The Stingray Nebula, formally known as Hen 3-1357, is the latest known planetary nebula in our air. However, Hubble images taken 20 years apart show a dramatic change in the shape and brightness of the nebula: Its once robust, clear blue clouds of interstellar dust and gas have almost disappeared, according to a statement from NASA.
“It’s very, very dramatic and very strange,” said Martín A. Guerrero, an astronomer at the Instituto de Astrofísica de Andalucía in Spain and team member on the ongoing analysis, said in the statement. “What we are seeing is the evolution of a nebula in real time. Over a period of years we are seeing variations in the nebula. We have not seen it before with the clarity we get with this view.”
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The recent study of the Stingray Nebula compares Hubble photographs taken in 1996 and 2016. The earlier photos capture bright, blue, fluorescent hydrogen gas clouds toward the center of the fog. But photos taken in 2016 show that the gas has almost disappeared, causing the nebula to appear smaller and duller. The shells of gas also lost their clear, wavy edges that brought the acquisitive namesake to the haze.
“Changes in nebulae seen before, but what we have here are changes in the fundamental structure of the nebula, ‘said Bruce Balick, lead researcher on the project and an astronomer at the University of Washington, Seattle, in the statement.
The Stingray nebula is composed of gas and dust that is expelled from its central star, known as SAO 244567. In general, the star will continue to heat the material as it expands to the outside, causing the gas and dust to ionize and glow.
Data from the Hubble images rapid changes revealed by the glowing nitrogen, hydrogen and oxygen shed by the dying star. Specifically, researchers found that the star’s oxygen emissions dropped by a factor of nearly 1,000 between 1996 and 2016, according to the statement.
“In most studies, the nebula usually gets bigger. Here it fundamentally changes shape and gets fainter, and on an unprecedented time scale,” Balick said. “On top of that, it doesn’t get any bigger to our surprise. Indeed, the once bright inner elliptical ring looks shrinking as it fades.”
When Hubble first photographed the Stingray nebula in 1996, researchers believed the image represented the final stage of life of SAO 244567, as the balloon cloud of clear gas through the dying star.
Now, however, it appears that SAO 245567 is declining in its stellar evolution, as recent observations show that the Stingray nebula has faded significantly, and that its brightest inner structure has shrunk instead of constantly expanding. The rapid changes observed in the nebula’s brightness and structure are thought to be caused by the cooling of the central star. As the star cools, it emits less ultraviolet ionizing radiation that would otherwise heat the emitted gas and make it glow.
A previous study, led by Nicole Reindl of the University of Potsdam, showed that the temperature of SAO 245567 rose between 1971 and 2002 from less than 40,000 to 108,000 degrees Fahrenheit. This temperature rise was probably caused by a short burst of helium fusion in the core of the star, which would help explain why the Stingray nebula appeared brighter in 1996, but has faded rapidly since then, according to the statement.
“We are very fortunate to be able to observe this at that very moment,” Reindl said in the new statement. “During such a helium shell flash, it evolves very fast, and that implies short evolutionary time scales, so we usually can’t see how these stars evolve. We happened to be there at the right time to capture it.”
A short period of helium fusion could have caused the outer layers of the star to swell and expel large amounts of gas and dust, causing the bright blue, fluorescent clouds of gas and dust observed in 1996. But in the 2016 photos, the Stingray nebula appears to be fading because the star is cooling now.
If the nebula continues to fade at the current rate, the researchers estimate that the structure will be barely observable within 20 or 30 years, according to the NASA statement.
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