Hubble investigates mystery of a dying star
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K648, the first planetary nebula discovered in a
globular cluster, is the pinkish object to the upper left of
the cluster core
(CNN) -- The Hubble Space Telescope has been enlisted to do
some detective work on a case that has baffled scientists for
years: a star dying a puzzling death in a globular cluster.
The star in question generated the first known planetary
nebula in a globular cluster, one of more than 100 dense
collections of stars that surround the Milky Way galaxy, Hubble researchers said Thursday.
Planetary nebulae are huge clouds of glowing gas that certain
kinds of stars emit near death. They are so named because
their shapes reminded 18th century astronomers using
primitive telescopes of planetary disks.
"It's a stage of life for stars at the very end. They become
very large giants and eject their outer layers, which exposes
the hot core of the star," said Hubble astronomer Mario
Livio. "Because it's hot, it ionizes the nebula to make it
shine, like a neon light."
While common in some parts of the universe, they remain
almost unknown in globular clusters because the clusters
possess few stars with enough mass to generate them.
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Low-mass dying stars lack the firepower necessary to heat
their nebulas enough to glow during the brief time such gas
clouds exist, about 10,000 years or so.
"They never become hot enough quickly to shine," Livio said.
Only four such nebulas are known to exist in globular
clusters, the first of which astronomer F.G. Pease
discovered in 1929 -- K648. It is located in globular cluster
M 15, about 40,000 light-years away in the direction of the
In this Hubble image, taken in December 1998, K648 is the
pinkish object to the upper left of the cluster core.
The remaining mass of K648 is about 60 percent of the sun,
barely enough to create a nebula, but much greater than most
stars in the cluster.
To found out why it has more mass, Hubble scientists used the
orbiting observatory to look for a nearby star that could
have donated a significant amount of mass.
"Presently, there is no known companion to this star," said
Livio, who offered an alternative explanation. "But we
believe in the past this star formed by the merger of two
The Hubble has spotted plenty of candidates for stellar
mergers in globular clusters, notably those known as blue
stragglers, which possess much more mass than astronomers had
expected, Livio said.
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Hubble Heritage Project
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