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Astronomers using NASA’s Chandra X-ray Observatory have spotted an ultrahot gas bubble at the center of a planetary nebula called IC 4593.
This composite image of the planetary nebula IC 4593 contains X-rays (Chandra) of the gas that has been heated to over one million degrees. These high temperatures were likely generated by material that flew off the star’s shrunken core and crashed into gas that had previously been ejected from the star. The Hubble visible light data in the image shows combinations of nitrogen, oxygen and hydrogen. Image credit: NASA / CXC / UNAM / J. Toala et al. / STScI.
IC 4593 is located approximately 7,800 light years away in the constellation of Hercules.
Also known as HD 145649 or IRAS 16093 + 1211, this object is the farthest planetary nebula detected by Chandra on X-rays.
Its hot bubble is one of the smallest of the planetary nebulae, in addition to BD + 30 3639, IC 418 and NGC 7027.
It contains gas that has been heated to over a million degrees.
These high temperatures were likely generated by material that flew off the original star’s shrunken core and crashed into gas that had previously been ejected from the star.
“IC 4593 is what we call a planetary nebula, a misleading sounding name because this class of objects has nothing to do with planets,” the astronomers said.
“The name was given about two centuries ago because they looked like the disk of a planet when viewed through a small telescope.”
“In fact, a planetary nebula forms after the interior of a star with about the mass of the Sun contracts and its outer layers expand and cool,” they said.
“In the case of the Sun, its outer layers could extend to the orbit of Venus during its red giant phase several billion years in the future.”
In addition to the hot gas, the researchers also found evidence of a point X-ray source at the center of IC 4593.
This X-ray emission has higher energies than the hot gas bubble.
The point source could come from the star that discarded its outer layers to form the planetary nebula or it could come from a possible companion star in this system.
“Deeper X-ray observations are needed to confirm the presence of a central X-ray emitting star in IC 4593 and to characterize its nature,” the scientists said.
“Such measurements could easily be provided by future X-ray missions such as Lynx and Athena.”
The study was published in Royal Astronomical Society Monthly Notices.
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JA Toalá et al. 2020. Chandra observations of the planetary nebula IC 4593. MNRAS 494 (3): 3784-3789; doi: 10.1093 / mnras / staa1024
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