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September 20, 1995
GL 105C: The Coolest Star?
HST, WFPC 2, D. Golimowski
Is the dim star to the upper right of this false-colour picture the coolest
possible normal star? From this recent picture by the
Hubble Space Telescope, astronomers have
estimated its mass is just high enough for it to fuse
helium in its core.
In general, the higher an object's mass, the higher it's core density and
temperature. Above a certain point, the intense core conditions cause
hydrogen atoms to move so fast that many stick or
"fuse" after collision,
releasing enormous amounts of energy. Were this object less massive, the
object would shine by gravitational contraction and so be termed a "brown
dwarf" rather than a normal main-sequence "star."
The star on the left is so much brighter than the
"coolest star" that it creates the white streak and dramatic pattern
visible in the image.
More information is
given by the Space Telescope Scientific Institute's
Tomorrow's picture: One Small Step
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