Monday, May 10, 2021

NGC 3918

NGC 3918 (also known as Hen 2-74, PN G294+04.7, and PK 294 + 04 1) is a planetary nebula, located at a distance of around 4,900 light years in the constellation of Centaurus. It was discovered on the 3rd of April 1834 by John Herschel.

The nebula is nicknamed the “Blue Planetary”, and it is the brightest planetary nebula that someone can observe in the southern sky. Thus, NGC 3918 can be observed even with a small amateur telescope easily, where you may see an oval shaped version of Neptune, due to color resemblance. 

The nebula is powered by its central star, which is on its transition phase from a red giant to a white dwarf. It has a central temperature of 117,000 Kelvin and over the next thousands of years, it will cool down significantly and become a white dwarf.

The nebula is composed of an inner shell that is inclined with respect to the observer (i.e., sky). On its polar regions there is a twin jet structure that most likely coevals with the inner shell. This indicates a common formation process of both the inner shell and the jet structure.

The outer component is fainter and it has a nearly elliptical shape and it displays faint protrusions.

Image: Composite optical image of NGC 3918 taken with the Hubble Space Telescope. The image was created using broadband optical filters, that are centred at 502 nm (B-band, blue), 555 nm (V-band,,green), 658 nm (R-band, red), and 814 nm (I-band, orange).

Image Credit: ESA/Hubble and NASA

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