Shown here is the nova shell of GK Persei (in the constellation of Perseus
around 1,500 light years away).
Only recently have astronomers unraveled the mysterious processes of novae and
their repeat performances. A classical nova outburst is created by a hot white
dwarf and a cooler companion that transfers mass (gas). The gas that falls
towards the white dwarf creates a circumstellar accretion disk.
When enough gas builds in the disk, conditions lead to hydrogen burning
and a thermonuclear runaway reaction (explosion). The shockwave and expanding
shell of hot gas create the firework-like structure of GK Persei. Typically
the explosions of classical novae are more frequent and thereby less energetic
since there isn't enough fuel in the accretion disk to cause a large explosion
like this. However, for whatever reason, GK Persei built up enough gas in
its disk to detonate back in 1901. Later in 1902 the expanding shell became
visible. At its maximum GK Persei ranked among the brightest stars in the
sky and the expanding gas reached velocities of 1200 km/s. Astronomers are
still not exactly certain why this shell is asymmetric and convoluted in
nature. This shell contains around 0.0001 solar masses.
Should a white dwarf like this manage to accrete the mass directly on to its surface it may blow up in dramatic fashion- such as Cassiopeia A .
|L R G B color production was used to create this image.||
Minimum credit line: Adam Block/NOAO/AURA/NSF
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