Not to be confused with Canadian Gum Hubba-Bubba, Hubble has released a great birthday image for it’s 26th birthday. I’m a few days late to celebrate, but it’s still a beautiful image.
Known as NGC 7653, the Bubble nebula is 8,000 light years distant in the constellation of Cassiopeia. The reason for this natural bubble shape is that the star just left of center in the image is ionizing a surrounding cloud of Hydrogen with it’s powerful stellar wind. As electrons and protons recombine at the edges of the bubble, they release an infrared photon that can be clearly seen by Hubble. Contrary to a supernova remnant, this bubble is not expanding. Since the star’s radiation spreads out, an equilibrium is reached between the ionizing starlight and the recombining protons and electrons, creating a boundary that doesn’t shift.
It’s a lovely image and a beautiful example of science explaining why we see it.