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On Earth, amethysts can form when gas bubbles in lava cool under the right conditions. In space, a dying star with a mass similar to the Sun is capable of producing a structure on par with the appeal of these beautiful gems.

As stars burn through their fuel, they cast off their outer layers and their cores begin to shrink. Astronomers using NASA’s Chandra X-ray Observatory and Hubble Space Telescope have found a bubble of ultra-hot gas at the center of one such expiring star in the Milky Way galaxy, a planetary nebula called IC 4593. Some 7,800 light-years from Earth, IC 4593 is the most distant planetary nebula detected with Chandra.

IC 4593’s superheated gas bubble – reaching temperatures of more than 1 million degrees Fahrenheit – invokes similarities to amethysts found in geodes around the globe. The nebula’s high temperatures likely were generated by material that blew away from the star’s shrunken core and crashed into gas previously ejected by the star.

Chandra also detected a point-like X-ray source, emitting even higher energies than the bubble of hot gas, at the center of IC 4593. Researchers suggest its source could be the remains of the star that discarded its outer layers to form the planetary nebula, or a possible companion star in the system.

A planetary nebula such as IC 4593 is deceptively named, given that the class of objects has nothing to do with planets. The phenomenon was inaccurately named about two centuries ago because of its resemblance to the disk of a planet when seen through small telescopes.

Planetary nebulae actually are formed after the interior of a star with approximately the mass of the Sun contracts and its outer layers expand and cool. When the Sun itself begins to cool several billion years from now, entering its red giant phase, its outer layers could extend as far as the orbit of Venus.

A paper describing these results was published in the April 2020 issue of the Monthly Notices of the Royal Astronomical Society. The multinational research team includes astronomers at Instituto de Radioastronomía y Astrofísica in Mexico; Instituto de Astrofísica de Andalucía in Spain; Johns Hopkins University in Baltimore; the Institute of Astronomy and Astrophysics in Taiwan; and Macquarie University in Australia.

Marshall Space Flight Center manages the Chandra program for the agency. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center in Cambridge and Burlington, Massachusetts, controls science and flight operations.

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