Do/Can Ringed Stars Exist?

The other night, while playing Elite: Dangerous, I came across a rather strange celestial body - one I never imagined possible.

It was a Brown Dwarf star with a very large ring.

Is something like this even remotely possible? Have such objects actually been seen?

It was also quite interesting that this star wasn't even the primary star in the system. It was orbiting a larger star (blue-white, I think), along with several planets.

• Now that I see the pictures, this looks somewhere in between a ring system and a circumstellar disk...which is appropriate given that the central body is a brown dwarf. Aug 11 '16 at 13:32
• @called2voyage This goes back to nailing down the definition of the two terms - how's it "in between"? Looks pretty solidly on the "ring" side to me.
– Iszi
Aug 11 '16 at 14:45
• It is difficult to tell from a picture, but this appears to extend well beyond the Roche limit. Aug 11 '16 at 14:46
• Compare to the size of Saturn's rings. Aug 11 '16 at 14:46
• If the Roche limit is really important to distinguishing the ring types, someone should address it in the definition question. As for measuring the exact difference, I'll see what I can do if/when I get back to the system. No guarantees though. (AFAIK the only way to really measure distance in-game is by checking the range of an object from the ship - and that is still a heat-radiating body in the middle there.)
– Iszi
Aug 11 '16 at 14:49

2 Answers

In a sense, that is what a circumstellar disk is.

Source: European Southern Observatory (ESO)

These are usually most noticeable around young stars as protoplanetary disks, disks that form planets. In the picture above, the gaps in the "rings" likely represent forming planets, similar to how the gaps in Saturn's rings indicate the presence of moons.

Our own star has a few "rings", though likely not as visually impressive: the asteroid belt, the Kupier belt, the scattered disk, and the Hills cloud.

That said, there are differences between these structures and the ring systems we are familiar with from planets. For example, rings are made of solid particles whereas protoplanetary disks contain a lot of gases. Rings may exist around "mature" planets, whereas protoplanetary disks represent an immature phase of planetary systems. Protoplanetary disks are not visible to the naked eye, whereas ring systems may be. In technical terms, a circumstellar disk is not a ring system.

• The "Hills Cloud" idea is sort of a tweak on the Oort Cloud, right? Aug 5 '16 at 13:25
• I'm going to cry a small foul on this one cause a traditional ring system is mostly inside the Roche limit and a Circumstellar disk is mostly outside, so this is something in formation not a semi-permanent ring system. Whether a star in it's main sequence can have a ring system is a tough question. I would think it would have to be a very cold star. A brown dwarf or just maybe a smaller luminosity or late in it's life red-dwarf. Aug 7 '16 at 23:00
• @userLTK That's a fair criticism, but a traditional ring system is not permanent either, precisely because it is inside the Roche limit. Also, not all circumstellar disks are considered "something in formation", though protoplanetary disks certainly are. Aug 8 '16 at 13:23
• @called2voyage: Permanency of the rings inside and outside the Roche radius is not an issue. What counts is that in a PP Disc the dust you see will coalesce into planets on very short (<10 Myr) timescale, due to interactions with the present gas, while a ring system outside its hosts Roche, has no gas, and hence wouldn't form larger bodies. Your comparison of PPDiscs with ring systems is physically wrong. Feb 4 '20 at 23:17
• @called2voyage: ??? How is 'what you see' relevant? The only thing that matters is physics. That is how we categorize objects. Btw you don't 'see' HL Tau like this. This is sub-mm emission, invisible to the eye. Feb 5 '20 at 0:15

There is a candidate ring system around the L-type brown dwarf G 196-3 B. According to Zakhozhay et al. (2017), the brown dwarf has a mass of ~15 Jupiters and a temperature of ~1870 K. They model it as being surrounded by a warm, narrow debris disc located close to the brown dwarf (~1280 K at a distance of ~0.12–0.20 solar radii).

Considering the derived global properties of the belt and the disc-to-brown dwarf mass ratio, the dusty ring around G 196-3 B may resemble the rings of Neptune and Jupiter, except for its high temperature and thick vertical height ($$\approx 6 \times 10^3\ \mathrm{km}$$).

G 196-3 B is located approximately 390 AU from the type M3 red dwarf star G 196-3.