Astronomy Picture of the Day |
APOD: 2000 September 10 - White Dwarf Stars Cool
Explanation:
Diminutive by
stellar standards,
white dwarf stars are also
intensely hot ...
but they are cooling.
No longer do their interior
nuclear fires burn, so they will
continue to cool until they fade away.
This Hubble Space Telescope image
covers a small region near the center of a
globular cluster known as
M4.
Here, researchers have
discovered a large concentration of
white dwarf stars (circled above).
This was expected - low mass stars, including the Sun,
are believed to evolve to the
white dwarf stage.
Studying how these
stars cool could lead
to a better understanding of their ages,
of the age of their parent
globular cluster, and
even the
age of our universe.
APOD: 2000 July 30 - NGC 2440: Cocoon of a New White Dwarf
Explanation:
Like a butterfly, a white dwarf star begins its life
by casting off a cocoon that enclosed its former self.
In this analogy, however, the Sun would be a caterpillar and the ejected shell of gas
would become the prettiest of all!
The above cocoon, the planetary nebula designated NGC 2440,
contains one of the hottest
white dwarf stars known.
The white dwarf can be seen as the bright dot near the
photo's center.
Our Sun will eventually become a "white dwarf butterfly",
but not for another 5 billion years.
The above false color image and was post-processed by Forrest Hamilton.
APOD: 2005 June 12 - M2-9: Wings of a Butterfly Nebula
Explanation:
Are stars better appreciated for their art after they die?
Actually, stars usually create their most artistic displays as they die.
In the case of low-mass stars like our
Sun and
M2-9 pictured above, the stars transform themselves from normal stars to
white dwarfs
by casting off their outer gaseous envelopes.
The expended gas frequently forms an impressive display called a
planetary nebula that fades gradually over thousand of years.
M2-9, a butterfly
planetary nebula 2100
light-years away shown in representative colors,
has wings that tell a strange but
incomplete tale.
In the center, two stars orbit inside a
gaseous disk 10 times the orbit of Pluto.
The expelled envelope of the dying star breaks out from the
disk creating the bipolar appearance.
Much remains unknown about the physical processes that cause
planetary nebulae.
Authors & editors:
Robert Nemiroff
(MTU) &
Jerry Bonnell
(USRA)
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NASA Official: Jay Norris.
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A service of:
EUD at
NASA /
GSFC
& Michigan Tech. U.