In 2001, observations at X-ray wavelengths by the Chandra X-ray Observatory revealed the presence of extremely hot gas within NGC 6543 with the temperature of 1.7×10⁶ K. It is thought that the very hot gas results from the violent interaction of a fast stellar wind with material previously ejected.
This interaction has hollowed out the inner bubble of the nebula.
Chandra observations have also revealed a point source at the position of the central star.
The spectrum of this source extends to the hard part of the X-ray spectrum, to 0.5–1.0 keV. A star with the photospheric temperature of about 100000 K would not be expected to emit strongly in hard X-rays, and so their presence is something of a mystery.
It may suggest the presence of a high temperature accretion disk within a binary star system.
The hard X-ray data remain intriguing more than ten years later: the Cat's Eye was included in a 2012 Chandra survey of 21 central stars of planetary nebulae (CSPNe) in the solar neighborhood, which found: "All but one of the X-ray point sources detected at CSPNe display X-ray spectra that are harder than expected from hot (~100000 K) central star photospheres, possibly indicating a high frequency of binary companions to CSPNe.
Other potential explanations include self-shocking winds or PN mass fallback."
In 2001, observations at X-ray wavelengths by the Chandra X-ray Observatory revealed the presence of extremely hot gas within NGC 6543 with the temperature of 1.7×10⁶ K. It is thought that the very hot gas results from the violent interaction of a fast stellar wind with material previously ejected. This interaction has hollowed out the inner bubble of the nebula. Chandra observations have also revealed a point source at the position of the central star. The spectrum of this source extends to the hard part of the X-ray spectrum, to 0.5–1.0 keV. A star with the photospheric temperature of about 100000 K would not be expected to emit strongly in hard X-rays, and so their presence is something of a mystery. It may suggest the presence of a high temperature accretion disk within a binary star system. The hard X-ray data remain intriguing more than ten years later: the Cat's Eye was included in a 2012 Chandra survey of 21 central stars of planetary nebulae (CSPNe) in the solar neighborhood, which found: "All but one of the X-ray point sources detected at CSPNe display X-ray spectra that are harder than expected from hot (~100000 K) central star photospheres, possibly indicating a high frequency of binary companions to CSPNe. Other potential explanations include self-shocking winds or PN mass fallback."
Cat's Eye Nebula