Monday, October 25, 2021

In the sky ghosts exist, but they are not scary!

Mirach's Ghost is in fact very little scary and due its name solely to its hazy appearance when viewed through a telescope.

Mirach's Ghost is in fact a galaxy (NGC 404) that is almost exactly on the same line of sight of Mirach, the second brightest star in the constellation Andromeda (in the photo NGC 404 is that blue-white spot in the upper left). Observing NGC 404 is made incredibly difficult by the star's presence, as its glow almost entirely obscures the light emitted by the galaxy.

However, the main telescopes, in particular Hubble, managed to study Mirach's Ghost, thus shedding light on its characteristics. This turned out to be a lenticular dwarf galaxy slightly smaller than the Small Magellanic Cloud, located 10 million light-years away from Earth. Unlike other galaxies of similar size, NGC 404 has some regions where star formation phenomena are active. This is interpreted by assuming that in the recent past NGC 404 has incorporated some smaller galaxies.

Credit: Kent Wood.

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