Ever heard of a Wolf-Rayet star? Neither had I. But I saw an image of this blue, circular, planetary nebula-like thing, and I knew I had to try to make one of my own.
What is a Wolf-Rayet Star?
A Wolf-Rayet star is among the hottest stars known. Relatively rare, these stars are so hot (20,000 to 210,000 K) that they have blown off their outer layers of hydrogen and are fusing helium or heavier elements in their cores. While extremely hot, these stars are not particularly bright visually due to the bulk of their radiation being in the ultraviolet wavelength.
The extreme heat causes prodigious stellar winds that result in an extreme rate of mass loss, with the outer layers of the star being expelled into space at a high rate. Consequently, many Wolf-Rayet stars are surrounded by halos of ionized gas. That blue circular formation in my image above is a shell of oxygen that was blown off the star in the past and is glowing due to radiation from the star.
WR-134, the star at the center of the blue halo, has a radius 5 times that of our sun, but is 400,000 times as luminous.
How Was This Image Created?
In my image, blue tones are from ionized oxygen, while red are from ionized hydrogen. So, how does one capture these colors? Through the use of filters, primarily.
The filter I used at the telescope during the process of creating this image was the Optolong L-eXtreme filter, which captures light from hydrogen and oxygen while excluding other colors, most of which come from artificial light sources such as city lights.
In total, I captured 22 hours and 30 minutes of exposure time in hydrogen/oxygen across 6 nights over 3 weeks in September 2025.
Interesting Details
Here, I’ve cropped in on the main feature of my image: the fascinating blue oxygen halo surrounding WR-134. As previously mentioned, this is a shell of oxygen that has been blown away from the star due to its intense radiation. That radiation is also ionizing the oxygen atoms, causing them to glow in the blue range of the visible light spectrum.
You can see streamers of gas within the outer ring, which I find really interesting. That patch of brighter blue at the 1 o’clock position on the ring is a bow shock where the gas flowing away from the star encounters interstellar material (the hydrogen gas that appears red in my image) and pushes up against it.
There are actually two other Wolf-Rayet stars in my image. In the crop to the left, the bright star on the right edge of the crop is WR-135, and the bright star at the left of the center of the crop is WR-137.
Note the curved feature near WR-137. That appears to be yet another bow shock that doesn’t show up as bright as the one near WR-134. In the future, I might work to more than double the overall exposure time on this image to see if I can bring out these subtle details even more.
Not a Planetary Nebula?
Why did I refer to the blue halo as a “planetary nebula-like thing” earlier? While it looks similar to a planetary nebula, the process by which this particular object was created is completely different than that which results in a planetary nebula.
A planetary nebula is created when a red giant star, near the end of its life, slowly expels its outer layers of gas, leaving behind a white dwarf star (the core of the red giant). The shell around a Wolf-Rayet star is created by a much more energetic process involving powerful stellar winds. The star is not a red giant near the end of its life, but a blue giant in the process of fusing heavier elements such as carbon, which will eventually end its life in a supernova explosion.
Needless to say, there’s a lot going on in this image. It’s a busy area of space, that’s for certain. When processing my image, I worked to make the hydrogen gas appear soft and cloud-like. I was going for a foggy appearance, as if the blue halo was floating in a fog bank. What do you think? Did I succeed? Use my contact page to let me know!
