I often hear about planetary ring systems, and even some moons might have them, but how about stars? Can a star also have rings?

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    Would you be willing to call the asteroid belt the Sun's ring system? – pela Dec 21 '15 at 10:14
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    @pela I upvoted your comment, but I wonder if the asteroid belt's distance from the Sun is too large compared with Saturn's distance from its rings. For example, Saturn's rings are closer to Saturn than all of Saturn's major moons, and the asteroid belt is further than 4 planets. – barrycarter Dec 21 '15 at 18:07
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    Most or all of the planetary ring systems we know about are within the planet's Roche limit. A star could have a ring of debris within its Roche limit, but it would probably be destroyed fairly quickly by light pressure and stellar wind. (The asteroid belt and the Kuiper belt as far outside the Sun's Roche limit.) – Keith Thompson Dec 21 '15 at 21:53
up vote 8 down vote accepted

They certainly can. A ring is often formed around a celestial body when its gravity rips apart another smaller celestial body. The Sun is really massive, so it could destroy any object that is not dense enough. Just Google about the Roche Limit for more informations (and better explanations).

Now, take a look at our solar system : You have the asteroid belt between Mars and Jupiter, and you also have the Kuiper belt beyond Neptune. Would you consider these being rings ? They sure are not as smooth as Saturn's, but to my mind, they still are rings.

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    Im pretty sure they are classed as rings - considering they are shaped around the sun like a ring. – Daniel Cann Dec 21 '15 at 13:42
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    Well but at the same time these were surely not created by ripping of some planet because otherwise Mercury would be ripped to pieces – Vojta Klimes Dec 21 '15 at 16:12
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    @VojtaKlimes : Mercury would not be destroyed because it has the right density to be above the Sun's Roche Limit. However, I agree with you on the fact that the asteroid belt is not made of broken planets. It is rather rocks that CANNOT agregate together because of Jupiter's gravity pull. – Nico Dec 21 '15 at 16:14
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    These are quantitatively different to Saturn's rings. The asteroid belt has a spread of inclinations of 20 degrees or so; many are in eccentric orbits. The Kuiper belt is flatter, but still nowhere near as flat as Saturn's rings. – Rob Jeffries Dec 21 '15 at 22:25
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    @Nico Yeah, you are probably right, did not thought of that – Vojta Klimes Dec 22 '15 at 11:51

The first star having rings seems to have been discovered in the late '90 by You-Hua Chu (University of Illinois). In Cosmic Catastrophes: Exploding Stars, Black Holes, and Mapping the Universe, Craig Wheeler wrote (in 2007):

[You-Hua Chu] scored another coup a decade later, at a meeting in Chile to celebrate the tenth anniversary of the discovery of the supernova, when she reported that she had discovered the first star to have rings around it, like the progenitor of SN 1987A.

SN 1987A was a supernovae that exploded in 1987. The progenitor (the star that actually exploded), Sk-69 20, was a blue supergiant. Pictures taken from Hubble showed three rings.

This video shows the lightning effect of the explosion on the inner ring from 1994 to 2016, that is, 7 to 29 years after the explosion (the ring is a few light years across while the most rapidly moving outer portions of the exploded star are moving at least at 10 percent of the speed of light - source: same book, p. 136).

This time-lapse video sequence of Hubble Space Telescope images reveals dramatic changes in a ring of material around the exploded star Supernova 1987A.

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