Thursday, July 8, 2021

The beautiful NGC 2392

When a star of similar mass to the Sun enters the final stages of its life, it expels its surface layers into space, forming a planetary nebula, while its core cools to become a white dwarf.

Among the most beautiful planetary nebulae in the sky is certainly NGC 2392, first described by William Herschel in 1787. Visible in the constellation Gemini, the nebula can already be seen through a small telescope as a small white spot with a central a faint star. To distinguish the details, however, it is necessary to use larger telescopes.

The structure of NGC 2392 is so complicated that astronomers have not yet been able to fully understand it. It consists of two concentric envelopes that partly overlap, responsible for the wonderful appearance of the nebula.

The two-shell structure is believed to be due to the different speed at which the nebula's gase and the stellar wind particles produced by the central white dwarf move. According to the measurements of the Hubble Telescope, the former would move at 115,000 km/h, while the latter at as much as 1.5 million km/h.

However, it still remains a mystery why some regions of the outer envelope seem to be denser than others (this can be understood from the difference in color). It has been speculated that this may be due to the collision of gas moving at different speeds.

Credit: NASA, ESA, Hubble.

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