Sunday, January 9, 2022

A celestial owl suspended in the darkness of space

Visible in the direction of the constellation Ursa Major about 2000 light years away from Earth, the Owl Nebula is one of the largest planetary nebulae discovered so far. In fact, the nebula has a diameter of over three light years and, by combining this data with that of the expansion rate of its gases, it was possible to obtain an age of 8000 years. Being so large, the nebula is very difficult to observe: the gases that compose it are in fact very rarefied and therefore its surface brightness is very low.

Thanks to this false color image obtained by the Liverpool Telescope we can study with great precision the structure of the nebula, which is easy to understand at first approximation.

The nebula can in fact be seen as the set of two concentric shells, the innermost one in blue and the outermost and very thin one in red. In particular, inside the first shell there are two areas arranged symmetrically with respect to the center of a blue color darker than the surrounding areas. These two regions, which appear darker since the density of the gas inside them is lower than the rest of the nebula, are responsible for the name Owl. In fact, when we observe the nebula through a telescope, what we see is a uniformly bright sphere with two darker circular regions inside it, which in some way resembles the eyes of an owl.

Credit: Göran Nilsson, The Liverpool Telescope.

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