# Closest stars to each other in different solar systems **URL:** \ **Category:** Factual Questions\ **Created:** [September 21, 2019, 11:59am UTC](https://boards.straightdope.com/t/closest-stars-to-each-other-in-different-solar-systems/840607 "2019-09-21T11:59:45Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![TaoPilot](https://avatars.discourse-cdn.com/v4/letter/t/77aa72/32.png) [@TaoPilot](https://boards.straightdope.com/u/TaoPilot)\ **Post date:** [September 21, 2019, 11:59am UTC](https://boards.straightdope.com/t/closest-stars-to-each-other-in-different-solar-systems/840607/1 "2019-09-21T11:59:45Z")
Proxima Centauri is the closest star to our own, being just over 4 light years away. Are there any two stars we know of that are closer to each other than that, that are not in the same solar system as each other? ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [September 21, 2019, 12:07pm UTC](https://boards.straightdope.com/t/closest-stars-to-each-other-in-different-solar-systems/840607/2 "2019-09-21T12:07:44Z")
I read somewhere - there’s some debate whether Proxima is actually in orbit with Alpha Centauri A and B or is just a randomly passing dwarf. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [September 21, 2019, 3:28pm UTC](https://boards.straightdope.com/t/closest-stars-to-each-other-in-different-solar-systems/840607/3 "2019-09-21T15:28:54Z")
In the same place? > **[Thorne–Żytkow object](https://en.wikipedia.org/wiki/Thorne%E2%80%93%C5%BBytkow_object)** > > A Thorne–Żytkow object (TŻO or TZO), also known as a hybrid star, is a conjectured type of star wherein a red giant or red supergiant contains a neutron star at its core, formed from the collision of the giant with the neutron star. Such objects were hypothesized by Kip Thorne and Anna Żytkow in 1977. In 2014, it was discovered that the star HV 2112, located in the Small Magellanic Cloud (SMC), was a strong candidate. Another possible candidate is the star HV 11417, also located in the S A Thorne... > [@](#): > > A Thorne–Żytkow object (TŻO or TZO) is a conjectured type of star wherein a red giant or supergiant contains a neutron star at its core, formed from the collision of the giant with the neutron star…A Thorne–Żytkow object is formed when a neutron star collides with a star, typically a red giant or supergiant. The colliding objects can simply be wandering stars. This is only likely to occur in extremely crowded globular clusters. I mean, obviously they are _now_ in the same system, but these objects are evidence of collisions, and some were chance encounters between wandering stars rather than binary systems. ---
**Author:** ![blue\_infinity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/blue_infinity/32/2817_2.png) [@blue\_infinity](https://boards.straightdope.com/u/blue_infinity)\ **Post date:** [September 21, 2019, 3:33pm UTC](https://boards.straightdope.com/t/closest-stars-to-each-other-in-different-solar-systems/840607/4 "2019-09-21T15:33:11Z")
The average distance between solar systems in the galaxy is about 5 ly. The average distance inside a globular cluster is 1 ly, and it gets more dense towards the centre. The core of a solar system is the heliosphere, which ends 100-200 AU from the sun, or 0.003 of a light year. So there’s a lot of extra room there. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [September 21, 2019, 7:05pm UTC](https://boards.straightdope.com/t/closest-stars-to-each-other-in-different-solar-systems/840607/5 "2019-09-21T19:05:34Z")
For a long time, the Sun was the closest known star to the Alpha Centauri system. But not too long ago, a brown dwarf (actually a double brown dwarf), [Luhman 16](https://en.wikipedia.org/wiki/Luhman_16), was discovered that was only 3.5 lightyears from AlphaC, making it closer to AlphaC than the Sun. > [@md2000](#): > > I read somewhere - there’s some debate whether Proxima is actually in orbit with Alpha Centauri A and B or is just a randomly passing dwarf. It’s not completely certain that Proxima is gravitationally bound, but the last report I saw (sorry, don’t have a link to the paper) says it probably is. As far as local stars that are fairly close, [Procyon](https://en.wikipedia.org/wiki/Procyon) is just over a lightyear from [Luyten’s Star](https://en.wikipedia.org/wiki/Luyten%27s_Star). In the not very distant past (astronomically speaking), there was the fairly close passage of [Scholz’s Star](https://en.wikipedia.org/wiki/Scholz%27s_Star) to the Sun. It approached to less than a lightyear about 70,000 years ago. In the future, [Gliese 710](https://en.wikipedia.org/wiki/Gliese_710) will approach to only about a fifth of a lightyear in about 1.3 million years. There are other stars that will get closer than AlphaC is right now in between now and Gliese 710’s approach, but I forget the name of the wikipage that summarizes them. Note: More exact numbers for the above figures can be found at those wikipages. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [September 21, 2019, 8:00pm UTC](https://boards.straightdope.com/t/closest-stars-to-each-other-in-different-solar-systems/840607/6 "2019-09-21T20:00:59Z")
> [@dtilque](#): > > There are other stars that will get closer than AlphaC is right now in between now and Gliese 710’s approach, but I forget the name of the wikipage that summarizes them. It was probably [this section](https://en.wikipedia.org/wiki/List_of_nearest_stars_and_brown_dwarfs#Distant_future_and_past_encounters) of the List of nearest stars. ---
**Author:** ![szabrocki](https://avatars.discourse-cdn.com/v4/letter/s/958977/32.png) [@szabrocki](https://boards.straightdope.com/u/szabrocki)\ **Post date:** [September 21, 2019, 8:10pm UTC](https://boards.straightdope.com/t/closest-stars-to-each-other-in-different-solar-systems/840607/7 "2019-09-21T20:10:27Z")
Are there any known 3 or more stars in the same gravitational solar system? ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [September 21, 2019, 8:20pm UTC](https://boards.straightdope.com/t/closest-stars-to-each-other-in-different-solar-systems/840607/8 "2019-09-21T20:20:57Z")
Sure. Castor, one of the two man stars in Gemini, is a bound system of six stars.(Sextuple). > **[Castor (star)](https://en.wikipedia.org/wiki/Castor_(star))** > > Castor is the second-brightest object in the zodiac constellation of Gemini. It has the Bayer designation α Geminorum, which is Latinised to Alpha Geminorum and abbreviated Alpha Gem or α Gem. With an apparent visual magnitude of 1.93, it is one of the brightest stars in the night sky. Castor appears singular to the naked eye, but it is actually a sextuple star system organized into three binary pairs. Although it is the 'α' (alpha) member of the constellation, it is fainter than 'β' (beta) Gemin... ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [September 21, 2019, 8:29pm UTC](https://boards.straightdope.com/t/closest-stars-to-each-other-in-different-solar-systems/840607/9 "2019-09-21T20:29:04Z")
How about the cluster of stars orbiting the black hole at the centre of the Milky Way galaxy? There are at least twenty of them, some of which pass very close to the black hole.Is that a single system? ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [September 21, 2019, 8:40pm UTC](https://boards.straightdope.com/t/closest-stars-to-each-other-in-different-solar-systems/840607/10 "2019-09-21T20:40:38Z")
S2 orbits Sagittarius A\* with a period of 16 years, only 30% longer than Jupiter around the Sun. So the center of our galaxy has some very close stellar orbits. Two white dwarfs with an orbital period of 6.91 minutes are so close to each other that the orbiting pair could fit inside Saturn. That is, inside the planet, not just inside the planet’s orbit. The pair is named ZTF J1539+5027 and was discovered just this summer. But I think Riemann has won the small distance contest here, with their entry of “0”. ---
**Author:** ![szabrocki](https://avatars.discourse-cdn.com/v4/letter/s/958977/32.png) [@szabrocki](https://boards.straightdope.com/u/szabrocki)\ **Post date:** [September 21, 2019, 9:04pm UTC](https://boards.straightdope.com/t/closest-stars-to-each-other-in-different-solar-systems/840607/11 "2019-09-21T21:04:17Z")
I can’t imagine the gravitational forces and radiation of all sorts in those multi star systems. Add a black hole it would be eventual doom to all the stars. Thank you all for the quick concise replies. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 21, 2019, 9:36pm UTC](https://boards.straightdope.com/t/closest-stars-to-each-other-in-different-solar-systems/840607/12 "2019-09-21T21:36:59Z")
“Contact binaries”, where the two stars are close enough to be touching each other, are fairly well-known, with several well-studied examples (the one I know best is [W UMa](https://en.wikipedia.org/wiki/W_Ursae_Majoris)). Of course, usually the stars in question are each much larger than Saturn, so that’s still something new. **szabrocki** , there’s no reason a black hole in such a system would mean doom. Stars are much more likely to collide with other stars than they are to fall into a stellar-mass black hole. A black hole’s orbit can be just as stable as any star’s, and a black hole in a stable orbit wouldn’t eat much of anything. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [September 21, 2019, 10:32pm UTC](https://boards.straightdope.com/t/closest-stars-to-each-other-in-different-solar-systems/840607/13 "2019-09-21T22:32:25Z")
> [@eburacum45](#): > > How about the cluster of stars orbiting the black hole at the centre of the Milky Way galaxy? There are at least twenty of them, some of which pass very close to the black hole.Is that a single system? That’s probably more of a mater of opinion. Personally, I’d say they’re part of the galaxy as a whole. After all, the entire galaxy is a gravitaionally bound system of several hundred billion stars and they all orbit the super massive black hole in the center. Of course, within the galaxy are smaller systems of gravitationally bound stars. [Globular clusters](https://en.wikipedia.org/wiki/Globular_cluster) are tightly bound systems of thousands of stars. [Open clusters](https://en.wikipedia.org/wiki/Open_cluster) are more loosely bound stars that will eventually evaporate and become [stellar associations](https://en.wikipedia.org/wiki/Stellar_association). The Sun was probably in an open cluster when it first formed and for some time thereafter. But I don’t think any of these are what the asker of the question had in mind. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 21, 2019, 10:37pm UTC](https://boards.straightdope.com/t/closest-stars-to-each-other-in-different-solar-systems/840607/14 "2019-09-21T22:37:41Z")
The supermassive black hole in the core is only a small fraction of the mass of the Galaxy as a whole. Most stars are orbiting the Galaxy as a whole, not specifically the black hole. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [September 21, 2019, 11:03pm UTC](https://boards.straightdope.com/t/closest-stars-to-each-other-in-different-solar-systems/840607/15 "2019-09-21T23:03:34Z")
The SMBH is at the center of mass of the entire galaxy, so it’s not unreasonable to say everything orbits that body. Yes, the gravitational details are much more complex than that, but they’re also more complex than saying “stars orbit the galaxy as a whole”. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [September 22, 2019, 7:26pm UTC](https://boards.straightdope.com/t/closest-stars-to-each-other-in-different-solar-systems/840607/16 "2019-09-22T19:26:38Z")
> [@szabrocki](#): > > […] Add a black hole it would be eventual doom to all the stars. […] Black holes aren’t special in their ability to attract things. Any mass does that. What’s special about a black hole is the landing – in a sense, there isn’t any, you keep falling forever, out the bottom of the universe. Or something like that. We need a poet to express it. However, falling into a star or planet is just as fatal as falling into a black hole, and orbiting a black hole is just as stable as orbiting a star or planet.