NASA’s Chandra X-ray Observatory image (left panel) of
the supernova remnant DEM L71 reveals a hot inner cloud
(aqua) of glowing iron and silicon surrounded by an outer
blast wave. This outer blast wave is also visible at optical
wavelengths (right panel). Data from the Chandra
observation show that the central ten-million-degree
Celsius cloud is the remains of a supernova explosion that
destroyed a white dwarf star.
DEM L71 presents a textbook example of the double-shock
structure expected to develop when a star explodes and
ejects matter at high speeds into the surrounding interstellar
gas. The expanding ejecta drive an outward-moving shock
wave that races ahead of the ejecta into the interstellar gas
(bright outer rim). The pressure behind this shock wave
drives an inward-moving shock wave that heats the ejecta,
seen as the aqua cloud.
The clear separation of the shocked matter and the heated
ejecta in the Chandra image allowed astronomers to
determine the mass and composition of the ejecta. The
computed ejected mass was found to be comparable to the
mass of the Sun. This and the X-ray spectrum, which
exhibits a high concentration of iron atoms relative to
oxygen and silicon, convincingly show that the ejecta are
the remains of an exploded white dwarf star. The size and
temperature of the remnant indicate that it is several
thousand years old.
Astronomers have identified two major types of
supernovas: Type II, in which a massive star explodes; and
Type Ia, in which a white dwarf star explodes because it
has pulled too much material from a nearby companion star
onto itself. If the mass of the white dwarf becomes greater
than about 1.4 times the mass of the Sun, it becomes
unstable and is blown apart in a thermonuclear explosion.
This was the case in DEM L71.
One of the major goals of the study of supernova remnants
is to determine the type of supernova explosion. The
identification of DEM L71 as the remnant of an exploded
white dwarf, or Type Ia supernova, represents a major step
forward in understanding more about the ways in which
stars explode.
The image and additional information can be found at:
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