The colour out of space. Image credit: NASA, ESA and Jes†¡s Ma†íz Apell†ániz (Instituto de Astrof†ísica de Andaluc†ía, Spain)
This fluffy pink blob is the star-forming region LHA-120-N 11 in the Large Magellanic Cloud some 170 000 light years from the Sun. N 11 (occasionally called the Bean Nebula) is about 1000 light years across. Take a moment to think just big that is!
What is the source of the delicate pink hue we see here and in so many other nebulae? Hydrogen is the main element making up such clouds. A typical hydrogen atom consists of a nucleus orbited by a much smaller electron just like a tiny solar system (this should not be taken too literally, as an accurate model it is about a century out of date, but it is still a useful visualisation of the situation). There is a certain amount of energy associated with the electron’s orbit and there are a series of possible orbits the electron can be in around the nucleus. Each has its own energy level, and note the electron must be in one of these levels or orbits, no intermediate positions are allowed (this is about as deep as I wish to tread in quantum mechanics). Sometimes an electron will change energy level. It jumps straight from one orbit to another, without moving through the intervening distance. Imagine Venus suddenly disappearing from its solar orbit and instantly reappearing in Mercury’s orbit and you will get the picture. Now too, you will realise where the often misused phrase “quantum leap” came from.
To balance the books, when the electron changes from a high energy level to a low energy level, the difference in energy must be removed. The atom gets rid of it by ejecting a photon, a particle of light, of exactly the right energy. For the most common such leap, the light of this energy has is a characteristic red colour of light. Emitted by hydrogen atoms when their electrons shift energy levels it is known as Hydrogen Alpha and is well-known to astronomers.
This soft pink glow is the by product of squillions and bazillions of electrons jumping around their atoms like hyperactive toddlers. Imagine that!
