The Iris Nebula, also called NGC 7023, was discovered by Sir William Herschel in 1794; the nebula is in the constellation of Cepheus, the King, in the northern sky. NGC 7023 is approximately 1400 light–years from Earth and about six light-years across. It is actually a cluster within the nebula LBN 487, and the nebula is lit by a magnitude +6.8 star, HD 200775, ten times the mass of our Sun. It is located near the Mira-type variable star T Cephei, and near the bright magnitude +3.23 variable star Beta Cephei (Alphirk – part of the Cepheus constellation).
It is not the only nebula in the sky to evoke the imagery of flowers, but within the iris, dusty nebular material surrounds a hot, young star. The dominant colour of the brighter reflection nebula is blue, characteristic of dust grains reflecting starlight. Central filaments of the dusty clouds glow with a faint reddish photoluminesence as some dust grains effectively convert the star’s invisible ultraviolet radiation to visible red light. Infrared observations indicate that this nebula may contain complex carbon molecules known as PAHs. The pretty blue petals of the Iris Nebula span about six light-years.
NGC 7023 is a reflection nebula, which are clouds of gas that are hot enough to emit light themselves. Reflection nebulae tend to appear blue because of the way light scatters, but parts of the Iris Nebula appear unusually red. Researchers studying the object are particularly interested in the region to the left and slightly above centre in the image, where they find dusty filaments to be redder than expected. An unknown chemical compound, most likely based on hydrocarbons, is responsible for the red tinge. The high resolution and sensitivity of Hubble’s instruments allow astronomers to study the area in detail.
This close-up of an area in the northwest region of the large Iris Nebula seems to be clogged with cosmic dust. With bright light from the nearby star HD 200775 illuminating it from above, the dust resembles thick mounds of billowing cotton. It is actually made up of tiny particles of solid matter, with sizes from ten to a hundred times smaller than those of the dust grains we find at home. Both background and foreground stars are dotted throughout the image.
Credits: Hubble, NASA, Wikipedia.