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After reevaluating my sense of perspective on sublight interstellar travel, I'm thinking of moving my planet closer to Earth to cut down on travel time and fuel costs. However, the planet my colonists are traveling to and the solar system it presides in have some very specific conditions.

Firstly, the star system itself is sextenary, composed of three binary pairs. Secondly, all three pairs orbit a central mass black hole with a mass of about 315 suns. Thirdly, this large black hole had to at some point in the past go hypernova, bombarding my planet with high energy particulates that caused various forms of exotic matter to appear in the crust of this young, embryotic planet.

Could a system like this exist anywhere within 10-20 lightyears of Earth? What are the odds that we wouldn't have detected it by now?

EDIT: Taking the suggestion to change to a single binary pair, what's the closest two stars orbiting each other could be to our solar system without having been discovered up until now?

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  • $\begingroup$ You're just to early in 2017 NASA plans to launch project TESS to locate close planetary systems. $\endgroup$
    – user23614
    Jul 31, 2016 at 10:50
  • $\begingroup$ The original title really didn't summarize the question very well, in my opinion. I think it's better now, but if you disagree, by all means feel free to edit further. $\endgroup$
    – user
    Jul 31, 2016 at 11:02
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    $\begingroup$ Little side-note: a good upper-limit for stellar masses in the current era is ~150 suns. So your central black hole would need to originate from a population III star, that formed, lived, and went hypernova in the early-ages of the Universe. $\endgroup$
    – Arcturus B
    Jul 31, 2016 at 18:55
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    $\begingroup$ @ArcturusB Or formed from the collision of several smaller black holes, as I addressed in my answer. $\endgroup$
    – ApproachingDarknessFish
    Aug 1, 2016 at 0:54
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    $\begingroup$ six stars orbiting a black hole - are we talking about a giant and really unlikely star system, or about a tiny galaxy devoured by Milky Way? $\endgroup$
    – John Dvorak
    Aug 1, 2016 at 5:45

5 Answers 5

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  • Could a system like this exist anywhere within 10-20 lightyears of Earth?

Well, space is big, there's certainly room for it. But the system you're describing seems incredibly dense. I'd be very surprised to find that much matter packed into one system outside of the galactic core.

  • What are the odds that we wouldn't have detected it by now?

Six stars, all orbiting an intermediate-mass black hole, within 20 lightyears? Impossible that we haven't detected it. Even if the system were 100% invisible, the gravitational pull of 315+ solar masses would make it blatantly obvious that something absolutely huge was hiding there. It would be the defining feature of our stellar neighborhood.

Also, if a star went hypernova and left a 315 solar mass black hole behind... that planet of yours, all six stars, and the entirety of the earth-sun system are all space toast.

Also, considering that the most massive star we know of is itself 315 solar masses, such a black hole could probably only form from the mergers of several smaller black holes. Perhaps instead of a hypernova, the planet could have been exposed to a black-hole merger event?

Suggestions:

This is a really creative setting and I'd love to see it work, so here are a few suggestions to make the scenario more believable.

I see two ways you could make this work:

  1. Create an alternate history in which astronomers have known about this system for centuries. The hypernova occurred aeons ago and the system migrated thousands of lightyears to reach our stellar neighborhood since then. You lose a connection to real world events, but physics is mostly preserved. I say mostly because it's still very questionable that such a system would be found in this part of the galaxy.

  2. Have a wormhole suddenly deposit the system into our galaxy from elsewhere. The hypernova occurred on the other side of the universe, where conditions beyond our current understanding of astronomy allowed the system to form as you have described. This way you maintain a connection to the real world and, considering that we really don't know what happens when black holes collide, technically don't violate any laws of physics as far as I know--you just make a few up.

Happy worldbuilding!

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    $\begingroup$ Minimum safe distance from a supernova (50~100ly) not achieved, +1 $\endgroup$
    – Mazura
    Jul 31, 2016 at 6:23
  • $\begingroup$ So really if I wanna stick to hard/relatively plausible science for both my planet and my interstellar travel (sublight antimatter propulsion), then I'd have to just remove the black hole entirely and maybe even cut it down to a single binary system instead of three pairs? Because it's gotta be within relatively close walking distance to Earth (metaphorically speaking) $\endgroup$
    – Z.Schroeder
    Jul 31, 2016 at 7:37
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    $\begingroup$ @Z.Schroeder - If you turn the black hole into a star, the WISE survey would've found it : "Discovery of an ultra-cool brown dwarf, WISEPC J045853.90+643451.9, about 10 to 30 light years away from Earth, was announced in late 2010 based on early data." $\endgroup$
    – Mazura
    Jul 31, 2016 at 10:32
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    $\begingroup$ @Z.Schroeder: if you go down to a single binary, it gets a lot easier. $\endgroup$
    – John Dallman
    Jul 31, 2016 at 11:03
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    $\begingroup$ Also, if a star went hypernova and left a 315 solar mass black hole behind... that planet of yours, all six stars, and the entirety of the earth-sun system are all space toast. - This is a relatively low-mass intermediate mass black hole (likely not formed from just one star), so it's likely at the center of some star cluster or small group of stars. Yeah, we'd definitely notice something wonky was going on with their orbits! $\endgroup$
    – HDE 226868 ♦
    Jul 31, 2016 at 22:28
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Odds are basically nonexistent.

From this list of nearby stars, there are perhaps 50 stars within the 10-20 lightyear range. The nearest discovered black hole is 2600 light years away, and its far smaller than the mass you mention.

The odds of finding a single system with a very particular 6 sun system and a black hole, completely undetected? Well, let me just say that Han Solo really didn't like me telling him the odds.

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Other posters of answers and comments have discussed the impossibility of a nearby massive back hole. Also, the hypernova has too many problems to be worth considering. This does not prevent there being three pairs of binary star system with the 10 to 20 light year range. This is reasonably plausible.

So how to do it? You can follow the example of previous science fiction authors. For example, Fred Hoyle and Geoffrey Hoyle's Fifth Planet (1963) has a planetary system called Helios, with a system of five planets, passing close to our solar system. Now this is something that hasn't, isn't or will not happen. The close passage of Helios happens in 2087.

If this had happened in the real world Helios would have been visible in our skies for millennia. It would have a major aspect of astronomy which it would have dominated culture, been part of our stories, and integral to history. Fred Hoyle was a major scientist and would have known he was rearranging the universe to make interstellar travel easier to do, for the story.

Basically you can do the same thing rearrange space within ten to twenty light years and add the three binary stars you want to have in your fictional future. Too many writers allow themselves to be dominated the tyranny of the real world, forgetting writers have the privilege of rejigging the world to better help their story to happen. Just take a list of the nearest stars within 20 light years and add your three fictional systems. Bingo!

If you want to devise a plausible means of slipping your three binary stars into being within 20 light years, just assume there is a compact, dense cloud of gas and dust that blocks seeing the three binary stars. The three binary stars can be relatively close to each other, or arranged in an approximate line of sight from our position in space to be blocked from observation, so effectively all three binaries are invisible. The dust cloud could be relatively close to the solar system as long as the three binaries lie along that line of sight.

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    $\begingroup$ I'm having a difficult time visualizing how three binary pairs, each by definition orbiting its center of mass, highly likely all three orbiting their common center of mass, could be positioned in such as way as to make detecting their true nature difficult enough that we wouldn't, yet somehow uninteresting enough that we don't spend any significant time trying. At the very least, the entire system would seem to appear as a variable star when seen from Earth. The period then would seem to be short enough to be noticable in human timeframes. $\endgroup$
    – user
    Jul 31, 2016 at 11:01
  • $\begingroup$ @MichaelKjörling Got it! I dropped the common centre of mass & assumed the three binaries lie along a line with respect to us. the model could be like this: Place each other separately along the line at 10, 15 and 20 light years apart. if there was a dense dust cloud on that line of sight, say closer to the Sun, at 1 or 2 light years, it could obscure the three binaries. This model preserves our knowledge of nearby stars & allows for the 3 binaries to be added in future. Just a big fudge factor. $\endgroup$
    – a4android
    Aug 1, 2016 at 5:16
  • $\begingroup$ The alternative to a great big fudge factor would be too simply assume the 3 binary systems have always been there. This is set in an alternative history. The other alternative is to make the existing red dwarf systems into being more interesting. Say, with habitable planets or resources worth colonising.. $\endgroup$
    – a4android
    Aug 1, 2016 at 5:19
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The only physical place such an assembly of stars could take place isn't in the stellar arms (where we are) but in a globular cluster, where tens of thousands of stars are packed in a tight grouping.

enter image description here

While the configuration you suggest is still unlikely (multiple binary stars orbiting a black hole), the odds of many stars and solar systems orbiting a central black hole seem pretty high. The view would be spectacular, with the sky so densely packed with stars that it would not be dark at night, and the central black hole (assuming you are close enough to orbit it but you are not living in an era where it is consuming large masses of gas or consuming stars, so the accretion disc would be minimal or quiescent) would provide a dazzling "Einstein ring" effect, magnifying the light of stars that pass through the ring to your location.

enter image description here

Of course there are several issues with living in this location. Firstly, the black hole itself is very dangerous. If there is enough infalling matter, an accretion disc will form, and the frictional energy of materials accelerating at high fractions of c will be emitting radiation in all wavelengths, subjecting planets to high levels of everything from infra red to x-ray radiation. Life will have a hard time establishing itself or evolving under a powerful barrage of radiation. The powerful gravitational field of the black hole will also have stars orbiting at tremendous speeds, so the odds of close stellar encounters disrupting planetary orbits is actually quite high.

enter image description here

Another, and more subtle issue is globular clusters are very old structures, and formed when there were far fewer "metallic" elements in the universe. Metal poor star systems will be lacking in most of the elements needed to support life, much less technology.

Finally, although the view is spectacular, globular clusters orbit the Milky Way at an average radius of 40 kiloparsecs (130,000 light-years) or more, which is sort of the opposite to the desired effect.

enter image description here

OTOH, if there is a means of accelerating a starship to very high fractions of c, the crew could have very little time pass while hundreds of thousands of years pass on Earth. John C Wright's "Count to a Trillion" series of books has a character waiting out a 70,000 year period while his love travels to and from a nearby cluster. Other hand waves, like hyperspatial wormholes or using the Alcubierre Warp Drive cold make the globular cluster accessible to the characters in the story.

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Definitely not.

A hypernova explosion only 10 to 20 lightyears from Earth would affect the Earth significantly and the impact of the radiation would give a clear signal here (even it it happened 100 Million years ago). The signal will consist of a combination of a mass extinction event with the deposition of sediments altered in their isotopical composition due to the creation of radionuclides.

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