Object name: NGC7635

Designation(s): NGC7635, BUBBLE_NEBULA,

The Bubble Nebula, NGC 7635 is a famous nebula in Cassiopeia. I find a range of distances for it from 7 to 11 thousand light-years. That results in a size ranging from 3 to 5 light-years. The bubble is being blown by the bright blue star to the upper left, far off center. The usual explanation is that the density of the material being blown by the stellar winds of the star are densest in this direction preventing its expansion being as rapid this direction. I\'m bothered by it still being rather round. I\'d expect it to be quite flattened this way. The star creating this bubble, SAO 20575 is an O star. These are extremely hot, supermassive but short-lived stars. Most of their light is emitted in the ultraviolet part of the spectrum so to our eyes it appears dimmer than it really is since we can\'t see ultraviolet light. The star is thought to be about 4 million years old and will only live some 10 million years, one thousandth as long as our much smaller star. It will end its life as a black hole. Until recently it was thought this meant it had to go supernova. Now we think some stars of this size go directly to the black hole stage without ever going supernova. Stick around another 6 million years and see what happens.

The bubble was found by William Herschel on November 3, 1787. It is in the second H400 program.

A three-dimensional simulation of the smaller bubble can be seen at https://www.nasa.gov/feature/goddard/2016/hubble-sees-a-star-inflating-a-giant-bubble

14\" LX200R @ f/10, L=6x10\' RGB=3x10\', STL-1100XM, Paramount ME