Free Astronomy Magazine January-February 2019

JANUARY-FEBRUARY 2019 SPACE CHRONICLES A lso known as the ghost of Cassiopeia, IC 63 is being shaped by radiation from a nearby unpre- dictably variable star, Gamma Cas- siopeiae, which is slowly eroding away the ghostly cloud of dust and gas. The constel- lation of Cassio- peia, named after a vain queen in Greek mythology, forms the easily recognisable “W” shape in the night sky. The central point of the W is marked by a dramatic star: here is Gamma Cassiopeiae. The remarkable Gamma Cassio- peiae is a blue-white subgiant vari- able star that is surrounded by a gaseous disc. This star is 19 times more massive and 65,000 times brighter than our Sun. It also ro- tates at the incredible speed of 1.6 million kilometres per hour — more than 200 times faster than our par- ent star. This frenzied rotation gives it a squashed appearance. The fast rotation causes eruptions of mass from the star into a surrounding disk. This mass loss is related to the observed brightness variations. The radiation of Gamma Cassio- peiae is so powerful that it even af- fects IC 63, sometimes nicknamed the Ghost Nebula, that lies several light years away from the star. IC 63 is visible in this image taken by the NASA/ESA Hubble Space Telescope. The colours in the eerie nebula showcase how it is affected by the powerful radiation from the distant star. The hydrogen within IC 63 is being bombarded with ultraviolet radiation from Gamma Cassiopeiae, causing its electrons to gain energy which they later release as hydro- ! T his image shows the sky around the nebula IC 63, nicknamed the Ghost Nebula. It was created from im- ages forming part of the Digitized Sky Survey 2. The field of view is dominated by the bright star Gamma Cassiopeiae, which is having a profound influence on IC 63. [ESA/Hubble, NASA, Digitized Sky Survey 2] gen-alpha radiation — visible in red in this image. This hydrogen-alpha radiation makes IC 63 an emission nebula, but we also see blue light in this image. This is light from Gamma Cassiopeiae that has been reflected by dust particles in the nebula, meaning that IC 63 is also a reflection nebula. This colourful and ghostly nebula is slowly dissipating under the influ- ence of ultraviolet radiation from Gamma Cassiopeiae. However, IC 63 is not the only ob- ject under the influence of the mighty star. It is part of a much larger nebulous region surrounding Gamma Cassiopeiae that measures approximately two degrees on the sky — roughly four times as wide as the full Moon. This region is best seen from the Northern Hemisphere during au- tumn and winter. Though it is high in the sky and visible all year round from Europe, it is very dim, so ob- serving it requires a fairly large tel- escope and dark skies. From above Earth’s atmosphere, Hubble gives us a view that we can- not hope to see with our eyes. This photo is possibly the most detailed image that has ever been taken of IC 63, and it beautifully showcases Hubble’s capabilities.