Fig11_6 Hot white dwarf revealed

Fig11_6 Hot white dwarf revealed

Fig. 11.6 . The expanding material in planetary nebula NGC 2440 has been cast off by a dying Sun-like star in episodic outflows and in different directions, revealing a central white-dwarf star. It is one of the hottest stars known, with a disk temperature of about 200,000 K that is more than 30 times hotter than our own Sunís photosphere. Ultraviolet radiation from the hot star has excited oxygen and nitrogen ions in the nebular gas, making them glow and fluoresce. Clouds of dust form long dark streaks pointing away from the central star. A much larger, cooler cloud of gas and dust remains dark and unseen in this visible-light image; it can be detected by its infrared radiation. (Courtesy of NASA/Hubble Heritage Team/AURA/STScI.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University