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novacyg.txt
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1996-01-12
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GAS SHELL AROUND NOVA CYGNI 1992
A NASA Hubble Space Telescope (HST) image of a rapidly ballooning
bubble of gas blasted off a star. The shell surrounds Nova Cygni 1992,
which erupted on February 19, 1992. The shell is so young it still
contains a record of the initial conditions of the explosion.
The HST image was taken in ultraviolet light with the European Space
Agency's Faint Object Camera (FOC) on May 31, 1993, 467 days after the
explosion. The FOC reveals a remarkably circular yet slightly lumpy
ring-like structure. The ring is the edge of the bubble's shell of hot
gas. The shell is only 37 billion miles across, or 400 times the
diameter of the solar system. A beam of light could cross the shell in
less than 2-1/2 days.
A striking relic of the explosion is an unusual bar-like structure
across the middle of the ring. It might mark the edge-on plane of the
orbits of the two members of the binary star system that triggered the
nova. An alternative possibility is that the bar is produced by twin
jets of gas ejected from the star and spanning the distance between the
shell and the star.
A nova is a thermonuclear explosion that occurs on the surface of a
white dwarf star in a double star system.
By knowing the shell's diameter, as calculated from a comparison
between its angular size and it expansion velocity (as measured from
ground-based observations) astronomers can precisely measure the
distance to Nova Cygni, which turns out to be 10,430 light- years.
Nova Cygni is located in the summer constellation Cygnus.
Credit: Francesco Paresce, ESA/STScI and NASA
PHOTO CAPTION STScI-PR93-21