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NGC 1818 (Globular Cluster)


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NGC 1818
Globular Cluster (球状星団)
OC OCL

別名 (Other names)
ESO 85-SC40 in LMC

明るさ (Brightness)
9.7等級

星座 (Constellation)
かじき座 (Dor) (Dorado)

NGC 1818 is a globular cluster in the constellation Dorado.

NGC 1818 (Globular Cluster) : Picture

NGC 1818: A Young Globular Cluster
NGC 1818: A Young Globular Cluster
(C) NASA
Globular clusters once ruled the Milky Way. Back in the old days, back when our Galaxy first formed, perhaps thousands of globular clusters roamed our Galaxy. Today, there are perhaps 200 left. Many globular clusters were destroyed over the eons by repeated fateful encounters with each other or the Galactic center. Surviving relics are older than any Earth fossil, older than any other structures in our Galaxy, and limit the universe itself in raw age. There are few, if any, young globular clusters in our Milky Way Galaxy because conditions are not ripe for more to form. Things are different next door, however, in the neighboring LMC galaxy. Pictured above is a "young" globular cluster residing there: NGC 1818. Observations show it formed only about 40 million years ago - just yesterday compared to the 12 billion year ages of globular clusters in our own Milky Way.

NGC 1818: Pick A Star
NGC 1818: Pick A Star
(C) NASA
This is NGC 1818, a youthful, glittering cluster of 20,000 stars residing in the Large Magellanic Cloud, 180,000 light-years away. Pick a star. Any star. Astronomers might pick the unassuming bluish-white one (circled) which appears to be a hot newly formed white dwarf star. What makes it so interesting? The standard astronomical wisdom suggests that stars over 5 times as massive as the sun rapidly exhaust their nuclear fuel and end their lives in a spectacular supernova explosion. With less than this critical mass they evolve into red giants, pass through a relatively peaceful planetary nebula phase, and calmly fade away as white dwarf stars like this one. Except that as a member of the NGC 1818 cluster, this new white dwarf would have evolved from a red giant star over 7.6 times as massive as the sun -- which should have exploded! Its discovery will likely force astronomers to revise the limiting mass estimate for supernovae upward.
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