During

white dwarfs once a Sun-like star has shed its outer layers as a planetary nebula, only the core region remains. Typically this is a ball of dense, hot matter, about the size of Earth and glowing intensely white dwarfs

White dwarfs are so faint that very few are within reach of amateur astronomers. In addition, two of the brightest (Sirius B and Procyon B) are companions of extremely bright stars. The easiest example to spot is Omicron2 Eridani.

name magnitude constellation

Sirius B 8.4 Canis Major procyon b 10.7 Canis Minor omicron2 Eridani 9.5 Eridanus van Maanen's Star 12.4 Pisces

NGC 2440 11.0 Puppis ip pegasi 14.0 Pegasus

Such white dwarf stars have surface temperatures of 180,000°F (100,000°C), but their small size makes them very hard to spot. Some have atmospheres of carbon, oxygen, and other elements created in their helium-burning phase.

Most are doomed to fade slowly over many millions of years, eventually becoming black dwarfs. However, white dwarfs in close binary systems sometimes have sufficient gravity to pull material from their companion stars. This may result in the white dwarf becoming a cataclysmic variable (see p.73).

dog star

The first white dwarf to be detected was Sirius B (circled here), companion of the brightest star in the sky. It could be detected from the wobble it causes in the orbit of Sirius A.

supernova remnants

When a star goes supernova, most of its material is torn to shreds and blasted across surrounding space to form a glowing ghost of the former star. The most famous supernova remnant is the Crab Nebula, created by a stellar explosion recorded by Chinese and native American astronomers in

Supernova Glowing Ghost

the cygnus loop

The Hubble Space Telescope captured this stunning image of the Cygnus Loop, remnant of a 5,000-year-old supernova.

ad 1054. Because they are composed of intensely hot gases, supernova remnants often emit most of their radiation as X-rays. As the hot gas speeds out across nearby space, it carries with it heavy elements from the supernova. These may collide with other interstellar gas clouds, perhaps even triggering another generation of starbirth.

the crab nebula

This spectacular photograph (left) shows the Crab Nebula, remnant of a 1,000-year-old supernova, seen through the European Southern

Observatory's Very Large Telescope in Chile.

the cygnus loop

The Hubble Space Telescope captured this stunning image of the Cygnus Loop, remnant of a 5,000-year-old supernova.

stellar life cycles

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