The ghost of Cassiopeia

At about 550 light-years from the constellation Cassiopeia, lies the IC 63, an amazing and slightly disturbing nebula. Also known as the Phantom of Cassiopeia, the IC 63 is shaped by the radiation of an unpredictable star nearby variable, Gamma Cassiopeiae, which slowly erodes the ghostly cloud of dust and gas. This heavenly ghost is the perfect backdrop for All Saints' Day, better known as Halloween.

The constellation Cassiopeia, named after a vain queen in Greek mythology, forms the easily recognizable form of the "W" in the night sky. The center point of the W is marked by a dramatic star called Gamma Cassiopeiae.

The remarkable Gamma Cassiopeiae is a blue-white variable star surrounded by a gaseous disc. This star is 19 times more massive and 65,000 times brighter than our Sun. It also runs at an incredible speed of 1.6 million kilometers per hour, more than 200 times faster than our parent star. This frenzied rotation gives it a crushed look. The rapid rotation causes mass eruptions of the star in a surrounding disk. This loss of mass is related to the variations of luminosity observed.

The radiation of Gamma Cassiopeiae is so powerful that it even affects the CI 63, sometimes dubbed the Ghost Nebula, located several light-years from the star. The IC 63 is visible on this image taken by NASA / ESA's Hubble Space Telescope.

The colors of the mysterious nebula show how much the nebula is affected by the powerful radiation of the distant star. The hydrogen contained in the CI 63 is being bombarded with ultraviolet rays of Gamma Cassiopeiae, causing its electrons to gain energy which they then release in the form of alpha hydrogen radiation, visible in red on this image.

This hydrogen-alpha radiation makes the IC 63 a transmitting nebula, but we also see blue light in this image. It is the light of Gamma Cassiopeiae that has been reflected by the dust particles in the nebula, which means that the CI 63 is also a reflection nebula.

This colorful and ghostly nebula slowly dissipates under the influence of the ultraviolet rays of Gamma Cassiopeiae. However, IC 63 is not the only object under the influence of the powerful star. It is part of a much larger nebula region surrounding Gamma Cassiopeiae, which is about two degrees in the sky, about four times the width of the full moon.

This region is best seen from the northern hemisphere in autumn and winter. Although it is high in the sky and visible all year round from Europe, it is very dark. The observation therefore requires a telescope large enough and a dark sky.

From the atmosphere above the Earth, Hubble gives us a vision that we can not hope to see with our eyes. This photo is probably the most detailed image ever taken of the IC 63 and is a perfect illustration of Hubble's capabilities.

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