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Space

Comets Can't Explain Weird 'Alien Megastructure' Star After All (newscientist.com) 412

schwit1 sends the latest news about KIC 8462852, the star that that led many to learn what a Dyson Sphere is. New Scientist reports: "The weirdest star in the cosmos just got a lot weirder. And yes, it might be aliens. Known as KIC 8462852, or Tabby's star, it has been baffling astronomers for the past few months after a team of researchers noticed its light seemed to be dipping in brightness in bizarre ways. Proposed explanations ranged from a cloud of comets to orbiting 'alien megastructures'. Now an analysis of historical observations reveals the star has been gradually dimming for over a century, leaving everyone scratching their heads as to the cause. Bradley Schaefer of Louisiana State University saw the same century-long dimming in his manual readings, and calculated that it would require 648,000 comets, each 200 kilometres wide, to have passed by the star — completely implausible, he says. 'The comet-family idea was reasonably put forth as the best of the proposals, even while acknowledging that they all were a poor lot,' he says. 'But now we have a refutation of the idea, and indeed, of all published ideas.' 'This presents some trouble for the comet hypothesis,' says Boyajian. 'We need more data through continuous monitoring to figure out what is going on.' What about those alien megastructures? Schafer is unconvinced. 'The alien-megastructure idea runs wrong with my new observations,' he says, as he thinks even advanced aliens wouldn't be able to build something capable of covering a fifth of a star in just a century. What's more, such an object should radiate light absorbed from the star as heat, but the infrared signal from Tabby's star appears normal, he says."
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Comets Can't Explain Weird 'Alien Megastructure' Star After All

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  • Now... (Score:5, Funny)

    by Anonymous Coward on Monday January 18, 2016 @12:11AM (#51320323)

    I'm not saying it's aliens but it's aliens!

    • I would check other stars close to this object for evidence of large defensive structures.

    • Re:Now... (Score:5, Interesting)

      by Anonymous Coward on Monday January 18, 2016 @12:34AM (#51320389)

      Schaefer makes two VERY large assumptions in discounting the alien megastructure theory. The first being that the energy storage inefficiency would be large enough to create large amounts of infrared light, and the second being that the megastructures in question would have been initially constructed around the star, instead of being moved into place afterwards.

      • Re: Now... (Score:5, Insightful)

        by guruevi ( 827432 ) <evi@noSPAM.smokingcube.be> on Monday January 18, 2016 @01:53AM (#51320559) Homepage

        That and that if you're capable of doing this you can't do 20% of a star in 100y time. Look at the advances we've made in computer and building technology, even space tech in the last century and we as a species are just starting. Give us a thousand years at the current rate of progress and if we haven't killed ourselves we can probably strip mine a planet like Mars to build our energy structures.

        • by gl4ss ( 559668 )

          but you would need to mine 100 planets like mars in the time, kind of.

          • Re: Now... (Score:5, Informative)

            by ShanghaiBill ( 739463 ) on Monday January 18, 2016 @03:56AM (#51320787)

            but you would need to mine 100 planets like mars in the time, kind of.

            Nope. Just one is enough. To build a Dyson sphere at one AU (the distance of the earth from the sun), or about 150,000,000 km, the sphere would have an area of 4 * pi * r^2 = 9e23 m^2. The mass of Mars is 6.39 × 10^23 kg. So if you build the sphere with a mass of about 1 kg / meter squared, you could do it with just a little over one Mars sized planet.

            • If we're strip-mining Jupiter, that's peanuts. Why Jupiter? We might want some fusion reactors for localized or pulsed power, or rocket fuel, and solar panels are lousy at providing both.
      • Re:Now... (Score:5, Interesting)

        by wierd_w ( 1375923 ) on Monday January 18, 2016 @04:55AM (#51320915)

        There's another possibility that's just as far out, and would explain the missing IR.

        It's a traffic hub for small FTL ships.

        If they use something like an alcubierre metric based warp drive, then the gravitational fields around the craft will scatter the star's light into vectors that are no longer straight lines away from the star. This will result in the star's effective brightness being reduced.

        Get enough of them going in and out of the system routinely, and you will get the observed phenomenon.

        To me, the obvious thing to do is look for gravitational waves coming from the system. If you can't catch their broadcasts (because they use something other than open channel radio), then look for the propwash.

    • by gtall ( 79522 )

      Yep, cue the Greek guy with the electric hair, he'd have no problems explaining this.

  • by ZecretZquirrel ( 610310 ) on Monday January 18, 2016 @12:14AM (#51320329)
    Tonight on the History Channel.
  • It's Primes (Score:3, Insightful)

    by justin12345 ( 846440 ) on Monday January 18, 2016 @12:21AM (#51320351)
    Send quantuum busters, we won't get a Second Chance.
  • even advanced aliens wouldn't be able to build something capable of covering a fifth of a star in just a century. --Summary

    So maybe the aliens aren't building it. Maybe they're just moving it... towards us...

    • I love it when people make judgements on the capabilities of an alien race. By definition, they are alien, so we can make no generalizations. But ostensibly since we can't conceive of a method of building a dyson sphere in 100 years, that means nobody else can either... Personally I bet someone screwed up and dropped a heavy element into the star with an errant stargate and now the star is going through death convulsions.
  • "just a century"? (Score:5, Interesting)

    by jeffb (2.718) ( 1189693 ) on Monday January 18, 2016 @12:30AM (#51320381)

    If you're willing to believe in a civilization capable of building a Dyson sphere, how much more of a stretch is it to believe they could do it in a few centuries? (We've just been seeing a dimming signal over that period, not complete extinction of the star's light.)

    I mean, yeah, I have some idea of the energies involved, and I'm not sure I can envision a process that would run at that pace producing anything other than streams of plasma at gamma-ray temperatures. But then again, I'm not sure I can envision a process that would digest entire planets worth of material and cast it into a shell at any pace. Good thing I didn't accept that particular process-design gig, I guess.

    • by bill_mcgonigle ( 4333 ) * on Monday January 18, 2016 @02:02AM (#51320571) Homepage Journal

      The surprise would be if a Class-whatever civilization that's building a Dyson Sphere hadn't already mastered self-assembling, self-replicating construction processes. There should be an exponential increase in the rate over time, if we haven't already missed that window. As the buildbots consume the planets, you just get more buildbots until the number is sufficient. Or if the sphere is to be made of the bots themselves then there's no need for a tail-off. Clarke called 'em monoliths when he had them eat Jupiter, but same idea.

      • by zmooc ( 33175 )

        Buildbots probably wouldn't consume planets; escaping from their gravity well would be much too costly compared to the alternatives. They probably would use asteroids instead, taking their time to tweak their orbits so they arrive at their destination processing plant with a minimum amount of energy. This would almost certainly not happen at an exponential rate. As with all mining, they would start with the low hanging fruit, causing production to become increasingly more difficult as time passes, prohibiti

      • by Viol8 ( 599362 )

        Thats all very well, but these buildbots still have to obey the laws of physics and self replication of complex objects simply can't happen that fast. It requires time and a boatload of energy and complex chemicals and material resources. You can't make something complex out of hydrogen unless each little bot has a mini fusion reactor on board which is pretty unlikely. Evolution has had 4 billion years to fine tune self replication on this planet with huge resources and sunlight, and yet even the fastest gr

    • If you're willing to believe in a civilization capable of building a Dyson sphere, how much more of a stretch is it to believe they could do it in a few centuries?

      Nah, they probably built replicators to accomplish the task. But then those replicators destroyed their civilization and are gradually surrounding the star with a Dyson sphere... made completely out of replicators.

    • What are the odds that not only can they build it in a span of a few centuries, but also that human civilization would exist and be able to observe the specific few centuries they build it over?

      • Re:"just a century"? (Score:4, Interesting)

        by Chrontius ( 654879 ) on Monday January 18, 2016 @04:06AM (#51320809)
        If they seeded our planet with life using FTL drives, the light of their civilization's dawn could just be reaching us now. If we accept the given of rare garden worlds, and cosmic gardening, the odds of seeing this are actually quite good.
      • Who knows how many pre-megastructure civilisations there are in the galaxy? There could be millions, each one thinking they are alone.

        • by arth1 ( 260657 )

          Who knows how many pre-megastructure civilisations there are in the galaxy? There could be millions, each one thinking they are alone.

          Increase that imaginary number by a few orders of magnitude, and there might be an explanation for dark matter there...
          But the question then becomes "why don't we see this happening every way we look?"

    • by gl4ss ( 559668 )

      and just do it at one star?

      doing it in span of 100 years makes no sense from energy use perspective.

    • If you're willing to believe in a civilization capable of building a Dyson sphere, how much more of a stretch is it to believe they could do it in a few centuries?

      You're all wrong - the star is clearly orbited by a huge swarm of teapots [wikipedia.org]. After all, we can't hope to understand the thinking of a race capable of building such a "Lipton Sphere" so you can't prove its not teapots.

      I'm not sure I can envision a process that would digest entire planets worth of material and cast it into a shell at any pace.

      PS: I thought the original Dyson Sphere concept was a huge cloud of satellites that eventually grew to capture most of the star's energy.
      PPS: The satellites could still be teapot-shaped.
      PPPS: The tea-cosies are blocking the infra-red. Nothing worse than cold tea.

    • I guess it could have been build over thousands of years, but most of the time when we haven't been recording it and when we did photograph the star 100 years ago covering parts of the star we couldn't see, and now the structure is rotating into our line of sight (possibly again) covering it a bit, until it rotates out of sight again. Or it could be a gas cloud that we are now seeing through at the worst angle. In both case it should slowly go away again as they rotate and or out viewing angle subtle change

  • Inconceivable! (Score:5, Insightful)

    by Anonymous Coward on Monday January 18, 2016 @12:38AM (#51320403)

    ... he thinks even advanced aliens wouldn't be able to build something capable of covering a fifth of a star in just a century.

    Clarke's first law: "When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong."

    • ... he thinks even advanced aliens wouldn't be able to build something capable of covering a fifth of a star in just a century.

      Clarke's first law: "When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong."

      Clarke's third law would also be appropriate: "Any sufficiently advanced technology is indistinguishable from magic."

  • by Anonymous Coward on Monday January 18, 2016 @01:22AM (#51320519)

    This star is larger than our Sun, yet it rotates thirty times faster. Its poles are significantly flatter, hotter, and brighter than the rest of the star. Thus a large object could block 22% of the star's light while covering a much smaller percentage of its disk. This also explains why the dips in the light curve are pointed on the bottom, not flat.

    There could also be a large unseen planet (i.e. one that does not transit the star from our point of view) pulling on the star's tidal bulge and causing its visible pole to slowly precess away from us. That would explain the gradual dimming.

    • ... hot pole ... bottom ... bulge ...

      That is all.

    • by D'Eyncourt ( 237843 ) on Monday January 18, 2016 @06:06AM (#51321087)

      There are a couple of problems with your ideas.

      Basically the most any planet in any star system could cover is approximately 2% of a star during a transit (as a comparison a transiting Jupiter seen from another star system would cover about 1% of the Sun). This is despite our estimate of when a planetary body would become massive enough to become a brown dwarf is about 80 times the mass of Jupiter because the mostly hydrogen gas in any gas giant is highly compressible. A planet with twice the mass as Jupiter would have a diameter only slightly larger than that of Jupiter, very much less than the 1.26 (= 2^[1/3]) growth that would be expected by simple linear growth.

      If a body instead were large enough to become a brown dwarf, then the interplay of the light being generated by fusion at its core becomes more important and its size would balloon out to many times that of Jupiter. And, of course, a brown dwarf would be easily detectable spectroscopically.

      Thus ANY planet in orbit around Tabby's Star that was transiting in front of it simply could not cause the brightness of the star to dip by as much as 22% as was once seen. There is the FAINT possibility that somehow what was observed was a planet within our own Kuiper Belt that happened to transit Tabby's Star during Kepler's observations, and that being MUCH closer to Earth than Tabby's Star's distance of about 1500 light years would allow it to cover more of that star, but there is the problem that a Kuiper Belt gas-/ice-giant should have been glaring obvious to our Spitzer Space Telescope which specializes in the infra-red range.

      Your idea of the dimmer poles precessing towards us contains contradictory ideas: the planet causing this somehow has to be massive AND close enough to cause this, and yet has to have an orbit that is at least a couple of hundred Earth-years in length. This "newly" detected dimming was determined from photographic plates taken at different times from 1890 to around 1990.

      My suspicion is that what we may be watching is a relatively short-lived (meaning less than tens of thousands of years) phase of Tabby's Star evolving from a main sequence star at the very earliest stage of becoming a (super-)giant. There is just barely enough helium accumulated at its core that its fusion only fitfully begins only to sputter out when the additional heat generated by that hotter fusion diffuses that core to below helium-fusion levels. Of course this "current" sputtering was generated tens to hundreds of thousands of years ago at the core (taking that long for the scattered light to reach the star's photosphere and thus become visible to us), but when helium fusion actually takes hold then the star ballooning out to become a (super-)giant will overtake that sputtering.

    • Nice point but how does that explain the increased dimming over a century
  • If it is not a group of objects shading a single star it could be multiple small luminous objects in a chaotic orbit close in around a black hole or some similar configuration that works if you reverse a few assumptions about what it could be. That would explain the absolute dimming effect without any infra-red getting past the shading object.
  • Planetary breakup? (Score:2, Insightful)

    by Anonymous Coward

    Roche limit reached about a century and a half ago, breakup continues. A super sized rocky planet which has migrated to within Mercury like distance of it's star and has subsequently been pulled apart. Put the planet in an orbit which is nearly edge on (which it would have to be to be detectable using these methods) and as the debris cloud increases in size the star is progressively dimmed (from our point of view) more and more.

    Seems the most obvious explanation.

    Interestingly, if you did want make a dyson

  • by Smiddi ( 1241326 ) on Monday January 18, 2016 @01:54AM (#51320563)
    This happened over 1,400 years ago!!
  • ...then we'll come to dinner.
  • a planet that's broken up, creating an asteroid belt?

  • by Gravis Zero ( 934156 ) on Monday January 18, 2016 @03:01AM (#51320679)

    maybe the star isn't screwed in tightly enough. just give it a half twist and see if that stops the flickering. ;)

  • I wish everyone would quit with the alien stories already.
    It's obviously ghosts.

    -

  • So basically, Kylo Ren is sucking the energy out of the star to make a new StarKiller?
    • Because if 3 destroyed Death Stars aren't enough, just try, try again...
      Oh and thanks for reminding me of how shit that movie was. What the fuck was the Starkiller, a planet converted to a space station, or a space station built to look like a planet? I though it was a planet, but then it wouldn't have any propulsion which makes it pretty stupid. Oh man I better stop before I start a rant... Fucking stupid movie....
      • Starkiller wasn't even the worst thing... but I won't say anything because my biggest complaints are all spoilers.
  • "...he thinks even advanced aliens wouldn't be able to build something capable of covering a fifth of a star in just a century. What's more, such an object should radiate light absorbed from the star as heat, but the infrared signal from Tabby's star appears normal, he says."

    Our grandparents couldn't imagine the technology that our children use today without thought.

    How much hubris does it take to believe that we know what kind of technology 'advanced' aliens - or even the grandchildren of our grandchildren

    • "A Logic Named Joe" by Murray Leinster (1946).

      Mr. Leinster, at least, seems to have imagined some of the technology that our children use today. And he was a decade older than MY grandparents (and I'll be a grandfather soon).

      But your point is still reasonable, if a longer timeline is used. Why should we expect that Charlemagne should have anticipated the modern world? And we should we think that we can anticipate the limits of the possible for our descendants in 1200 years (for those of you who are una

      • A fifth of the star in a century implies some numbers regarding minimum amount of mass necessary and the energy to move that mass. What I've seen elsewhere says that if there were going to be, say, a Dyson ring or Dyson sphere built that quick, the mass would have to be already in place, meaning the star would already be dimmed. Oh, there are some outside ways to compensate, which is why alien megastructure is still a possibility, but they're pretty extreme energy balances that we think we'd see being expen
        • Oh... and it might not be alien megastructures. It might be human megastructures after we invented time travel. Once we say "well, anything might be possible in the future", we open the door to all sorts of conjecture. There's brainstorming and then there's reasonable suspicion. At this time, alien megastructure is just brainstorming. Keep looking for data!
  • What if what we're seeing is not inherent dimming of the star from its own internal processes or by its own orbital objects and cloud, but by objects closer to home? In particular, is it possible that a particularly dense portion of the Oort cloud has slipped between the star and us? We're only starting to get a handle on Kuiper belt objects. We really have no idea what's in the Oort cloud or how it's distributed.

    • by abies ( 607076 )

      Not sure about exact proportions, but Earth is rotating around the Sun. I have a feeling that anything in Oort cloud, big enough to dim that star regardless of position of Earth around a Sun, would also dim certain others stars nearby (in angle terms).

  • "I just don't feel like shining any more. I'm watching the sentients on my local planet, and they're just mean to each other. It's so sad to watch. I give up. I'm tired of burning hydrogen for these ungrateful whelps. All this fusion for them is giving me iron streaks! Not worth it. I'm going to go spend a few petaseconds focused on some other projects that are less work intensive for me."

  • "...he thinks even advanced aliens wouldn't be able to build something capable of covering a fifth of a star in just a century..."

    So, alien megastructures are a possible theory here, but for some reason we want to sit back and believe that construction is the main reason the theory is bunk?

    No wonder people on this planet still believe aliens built the pyramids. Seems rather stupid and ignorant to even theorize about limits of alien capability.

    Speaking of construction, 100 years ago humans were still marveling at the internal combustion engine...not that we "dumb" humans have really done anything with that technology in the last centu

  • Seems rather conceited for us to say "there's no way they could cover 1/5 of a star in a century" when little more than a century ago one could have found plenty of 'experts' who would poo-poo the idea of powered flight.
    Hell, only 30 years ago, nearly every single civilian phone in the world was somehow attached to a wall.

    And as far as his comments about black-body radiation from such a structure, it doesn't seem terribly unreasonable for a civilization capable of such engineering such a megastructure in th

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