NGC 7635 – The Bubbles Nebula

Before you start correcting me, the -s- in the title is meant to be there ;-)

This well loved object eluded me for two seasons. Not because it is dim (on the contrary), but because first my STC-Duo filter and later my L-Enhance filter gave me unrecoverable halos around the central star. With my IDAS-NBZ filter, the situation is a lot better. I processed the Ha and OIII signals on their own and combined them in a color scheme to my liking to bring a bit of a 3D feeling to the picture. 

As for the title: There is a nice write-up in Annals of the Deep Sky Vol 4, which I will not repeat here. (In short, the bubbles are formed by strong winds from a massive young O star  BD+60 2522 - the one in the bubble, next tot he finger like object. Strong radiation from this star creates a larger ionised cavity.)
What I do like to add is some new insights that were gained after the publications of this Annals volume in 2016. In Annals, the proper motion of the central star at the time still had a factor 2 uncertainty, leading to multiple explanations of the position of the star in relation to the bubble. Since then, the Gaia mission has delivered better astrometric data on this subject.

Here I present some results from a more recent study (see link below). Part of this study was high resolution spectroscopy at various positions in the bubble. The velocities derived from these measurements show not one bubble, but a multiple set of bubble structures.  As from the Gaia measurements, BD+60 2522 has a very high velocity (“runaway O star”) and the authors of the linked paper suggest the following interpretation: The fast moving star has had several outbursts of mass-loss while moving and/or its stellar winds have collided with non-uniform interstellar medium while the star travels through it. More like a whale blowing bubbles while swimming than a blown piece of bubblegum!  

Link to the research paper: https://arxiv.org/pdf/2003.06371.pdf