(ORDO NEWS) — An international team of astronomers has discovered a rare planetary nebula inside the open star cluster M37, which is the oldest known planetary nebula.
The discovery is reported in an article published in the Astrophysical Journal Letters.
The planetary nebula is a cloud of ionized gas that surrounds a white dwarf.
About four thousand planetary nebulae are known in the Milky Way, but the object IPHASX J055226.2+323724 is only the third nebula associated with an open cluster.
IPHASX J055226.2, like the other two planetary nebulae in open clusters, is bipolar, that is, it has the shape of a butterfly.
It also has a type I chemical composition, meaning it is enriched in elements heavier than helium. All this indicates that the progenitor star had a mass of about 2.8 solar masses.
The kinematic age of the nebula is estimated at 70,000 years, based on the rate of expansion of the nebula, assuming that the rate has changed little since the start, when the parent star first shed its outer shell of gas.
It is believed that the typical lifespan of a gaseous nebula reaches 5-25 thousand years. The extended lifespan may be due to the location of the nebula in a star cluster.
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