Imaginea Astronomica a Zilei

Descopera cosmosul! In fiecare zi este prezentata o noua imagine sau fotografie a universului nostru fascinant, insotita de o explicatie scurta din partea unui astronom profesionist.

2003 May 31
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NGC 1818: Pick A Star
Credit: R. Elson and R. Sword (IoA Cambridge), NASA

Explicatie: (Edit) 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.

Imaginea de maine: spinning black hole


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Autori & editori: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
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& Michigan Tech. U.