Astronomers using NASA’s Chandra X-ray Observatory have spotted a bubble of ultrahot gas at the center of a planetary nebula called IC 4593.
This composite image of the planetary nebula IC 4593 contains X-rays (Chandra) from gas that has been heated to over a million degrees. These high temperatures were likely generated by material that blew away from the shrunken core of the star and crashed into gas that had previously been ejected by the star. Visible light data from Hubble in the image show 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 in X-rays by Chandra.
Its hot bubble is one of the smallest among planetary nebulae, besides 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 blew away from the shrunken core of the original star and crashed into gas that had previously been ejected by the star.
“IC 4593 is what we call a planetary nebula, a deceptive-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 is formed 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 as far as 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 for point-like X-ray source at the center of IC 4593.
This X-ray emission has higher energies than the bubble of hot gas.
The point source could be from the star that discarded its outer layers to form the planetary nebula or it could be from a possible companion star in this system.
“Deeper X-ray observations are needed to confirm the presence of an X-ray-emitting central star in IC 4593 and to characterize its nature,” the scientists said.
“Such measurements could easily be provided by future X-ray missions as Lynx and Athena.”
The study was published in the Monthly Notices of the Royal Astronomical Society.
_____
J.A. Toalá et al. 2020. Chandra observations of the planetary nebula IC 4593. MNRAS 494 (3): 3784-3789; doi: 10.1093/mnras/staa1024
