I know that kind of green is Halpha but why is it in a ring like that? camera artifact?


Hmm, thats an interesting one. Could be a PN with strange morphology or maybe a collisional ring.


It’s a planetary nebula (click on the map, follow the “Look up in Simbad” link) – named “PN SuWt 3” (after the people who discovered it, Schuster & West). I don’t know much about PNe, but you could get an elliptical shape like that if it’s really a ring viewed at an inclined angle. According to the wikipedia page on planetary nebulae, the details of how they get their shapes isn’t really well known, but a ring could be the result of a binary star system (somehow), because that at least give it one special axis!


PS, that is SO COOL!


Should be a singular WD. When you have 2 white dwarfs in a binary system in the centre of a PN, you can get interesting shapes like hourglasses.

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Is this the diamond necklace nebula that has been imaged by Hubble? If it is, it is a shock wave slamming into a ring of ejecta from the star at the centre of the image… or it could be another similar object?

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Nice planetary nebula. :slight_smile:

Green color of objects with z~0 (objects in our galaxy) is from the r-band, which covers the H-alpha line. So this is the glow of hydrogen atoms.

Here is the H-alpha image from VPHAS+
Dataset: ESO Dataset

Btw. H-alpha filter only lets light through with a specific wavelenght (at around 656 nanometers), while the r-Sloan filter lets a range of wavelengths trough (between 559 nm and 675 nm).


I remember a similar nebula, which was found in the Milky Way Project and dubbed “Eye of Sauron” PN WRAY 17-56

MWP link:


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I think you are referring to SN 1987A, which is a supernova remnant and not a planetary nebula. No idea where the second image comes from. It would be helpful if you link to the source website from which you got those images.

Only some massive stars do eject a ring before they go supernovae. I never heared that AGB-stars or a red giant ever did something similar before they formed a planetary nebula.

SN 1987A is located in the Large Magellanic Cloud, while DECaPS only looked at the galactic plane.


Btw. PN SuWt 2 is also a ring.

It is a bit more well studied and has an eclipsing binary in the center (Exter et al. 2010).

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Addition: SuWt 2 with CTIO/NOAO 1.5m telescope:

Train of links gets you to the Hubblesite release (without any Hubble image)

I collected the images some years ago, from Hubblesite.org. There are videos of the shock wave from the supernova hitting the ring of ejecta sent out by the dying star thousands of years earlier.

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Ah, ok.

Yes, I know these animations of SN 1987A.

Planetary Nebulae are much more gentle. It is much more like a strong stellar wind that expels the outer layers over thousands of years.

From what I could read from Exter et al: There are probably some similarities here, but the mechanism how the ring formed seems to be different? Did SN 1987A involve a binary or was it a single star that exploded? For SuWt2 the evolution involves a triple system and probably the termination of the AGB stage during the common envelope (CE) phase. So SuWt 2 is a rare ePCEB.

Also read the wikipedia article Post common envelope binary (PCEB), which I basically wrote. I think these systems usually form bipolar nebulae (shaped like tubes), that are connected at the base by a flat annular disk-like feature, which is oriented perpendicular to the bipolar features (see the graphic from the hubblesite that I posted). Sometimes the bipolar features are more prominent and sometimes the disk-like feature is more prominent.


Thanks for the links. As a physicist I have often pondered over the origins of the forces that cause the formation of the huge structures seen in Hubble images and especially radio telescopes. Space is obviously a much more dynamic environment than it appears to be to the human eye!