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These images portray
examples of the most commonly detected sources of EUV radiation - Cool
Stars with Hot (Active) Coronae, White Dwarf Stars, and Cataclysmic Variable
Stars. Active stellar coronae are typical of many stars with late spectral
types (F, G, K and M). Despite these stars' cool surface temperatures,
they have hot outer atmospheres which emit EUV radiation.
In the image of
our own Sun (spectral type G) during a total solar eclipse (top-left),
we can see the Sun's corona, or outer atmosphere, which may be strongly
affected by magnetic fields. The EUVE spectrometer telescope has allowed
astronomers to observe the active and hot coronae of many other stars like
our Sun, helping them understand the underlying physical mechanisms responsible
for the active coronal regions.
Among the unusual
objects that the EUVE satellite has studied are the dense, Earth-sized
remnants of red giant stars - hot white dwarfs. A white dwarf star has
nearly the mass of the Sun compressed into a volume the size of the Earth.
A teaspoon of this very dense white dwarf material would weigh tons on
Earth. An artist conception of a white dwarf star, compared to the Earth
for scale, is shown on the top-right. Our own Sun is expected to turn into
a white dwarf in about 5 billion years. During the white dwarf stage of
a star's life, the surface temperature can reach 100,000 degrees Kelvin,
making it a bright emitter of EUV radiation.
A model of a cataclysmic
variable star is portrayed at the bottom of this image as envisioned by
an artist's conception. In such a binary star system, the infall of matter
from a star onto a white dwarf companion produces extreme ultraviolet radiation
that is detected by the EUVE satellite.
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