Chandra X-ray observations of a remarkable planetary nebula called NGC 2392 have revealed superheated gas around the dense, hot core of the nebula.
This image combines data from two different observatories: Chandra X-ray data – purple; Hubble data – red, green, and blue. X-ray data from Chandra reveal the location of million-degree gas near the center of the planetary nebula. Hubble data show the intricate pattern of the outer layers of the star that have been ejected (X-ray: NASA / CXC / IAA-CSIC / N. Ruiz et al; optical: NASA / STScI)
NGC 2392, also known as the Eskimo Nebula or the Clownface Nebula, is located in the constellation Gemini some 4,200 light years from us.
Planetary nebulas form when a star uses up all of the hydrogen in its core – an event our Sun will go through in about 5 billion years. When this happens, the star begins to cool and expand, increasing its radius by tens to hundreds of times its original size. Eventually, the outer layers of the star are carried away by a 50,000 km per hour wind, leaving behind a hot core. This hot core has a surface temperature of about 50,000 degrees Celsius, and is ejecting its outer layers in a much faster wind traveling 6 million km per hour. The radiation from the hot star and the interaction of its fast wind with the slower wind creates the complex and filamentary shell of a planetary nebula. Eventually the remnant star will collapse to form a white dwarf star.
The new X-ray data from NASA’s Chandra X-ray Observatory, published in the Astrophysical Journal, reveal the location of million-degree gas near the center of NGC 2392.
The observations were part of a study of three planetary nebulas with hot gas in their center. The results show that NGC 2392 has unusually high levels of X-ray emission compared to the other two. This leads researchers to deduce that there is an unseen companion to the hot central star in NGC 2392.
Astronomers believe the interaction between a pair of binary stars could explain the elevated X-ray emission found there. “Meanwhile, the fainter X-ray emission observed in the two other planetary nebulas in the sample – IC 418 and NGC 6826 – is likely produced by shock fronts in the wind from the central star.”
______
Bibliographic information: N. Ruiz et al. 2013. Detection of Diffuse X-Ray Emission from Planetary Nebulae with Nebular O VI. ApJ 767, 35; doi: 10.1088/0004-637X/767/1/35
