A Predator and Its Prey
Sh2-129 is a large, faint emission nebula that resembles a bat in mid-flight. However, it became world-famous in 2011 when amateur astronomer Nicolas Outters discovered a faint, bipolar outflow of Oxygen gas shaped exactly like a giant squid (Ou4) nested right in the center. The Squid is actually a massive bipolar outflow from the triple star system HR 8119. It is one of the largest such structures in the sky, but it is so faint that it remained hidden from professional telescopes for decades.
Imaging Challenges
- • Extreme Faintness (Ou4): The Squid (OIII) is significantly fainter than the Bat (Ha). You need a massive amount of integration time to even see its outline.
- • Processing Separation: The Bat is deep red, while the Squid is pale teal. If you over-process the red channel, you will 'drown' the Squid.
- • Signal-to-Noise: Because the OIII signal is at the very edge of detection, you will need to use heavy noise reduction while being careful not to erase the faint 'skin' of the squid.
For a long time, astronomers weren't sure if the Squid was inside the Bat or just behind it; recent data suggests they are physically located at the same distance.