Astronomy Picture of the Day

Explanation: The Hubble Double Bubble Planetary Nebula is bubbling over with excitement. More mundanely known as Hubble 5, this bipolar planetary nebula is being created by a hot wind of particles streaming away from the central star system. The hot gas expands into the surrounding interstellar medium in a fashion similar to the inflation of hot air balloons. A supersonic shock-wave can form at the boundary, causing newly excited gas there to shine as electrons recombine with resident elements. In the above picture, colours are assigned according to the energy of the recombinant radiation. This star system lies about 2200 light-years from Earth, and likely includes a Sun-like star slowly transforming itself into a white dwarf.