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

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."

Comments

Now...

[Anonymous Coward]

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

Re:Now...

[Anonymous Coward]

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...

[guruevi]

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.

Re: Now...

[tysonedwards]

Our star loses one billion kilograms per second... While that may sound like a lot... It's still only an earth mass every 150 million years. The math doesn't work out. Additional matter would need to come from somewhere.

Re: Now...

[ShanghaiBill]

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.

Re:Now...

[wierd_w]

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.

Re:Now...

[dreamchaser]

I know you're joking, but sending nukes to attack a civilization with engineering advanced enough to build a Dyson Sphere or other mega-structures would probably be like ants developing the technology to throw grains of sand at relatively low velocities at us.

Re:Now...

[silentcoder]

Considering that even if we could launch nukes at light-speed (Which we can't - nothing remotely close) they wouldn't get there for a millenium and a half - it's already too late.

Whatever it is we're witnessing now, actually happened around 600AD - when we were busy trying to invent a better horse-collar.

Re:Now...

[ewibble]

A nuke would not be very destructive at all, our sun is 1,300,000 times larger than the earth (so about 11911 times the surface area) a dyson sphere is larger than the star. When they say we have enough nukes to destroy the earth many times over they don't mean blow it into tiny pieces just destroy all life on earth.

Also a structure that size would have to withstand large astronomical objects hitting it from time to time.
if a large 16km asteroid it the earth it would be equivalent to a 200 Million megaton impact(http://www.astronomycafe.net/qadir/q975.html) the biggest nuke ever made is only 50 megatons, that is 4 million times more. Even a 75 meter asteroid has a 100 Megaton impact. Basically if we could send a nuke that far into space the kinetic energy would probably be more than the explosion. And an object that size would be already dealing with things much bigger than a nuke on a regular basis.

also from here http://www.space.com/51-astero... asteroids can reach up to 940 km across, not 16km.

Alien Megastructures:

[ZecretZquirrel]

Tonight on the History Channel.

Re:Alien Megastructures:

[Applehu Akbar]

"Tonight on the History Channel."

But where does Hitler come into it?

Re:Alien Megastructures:

[lord_mike]

It's a secret weapon of the Luftwaffe... tonight at 8pm.

Re:Alien Megastructures:

[PolygamousRanchKid]

Accually, the Luftwaffe did build an airbase on the Moon: https://en.wikipedia.org/wiki/...

However, the whole project got derailed, when the astronauts discovered the nudist colony on the Moon: https://en.wikipedia.org/wiki/...

They had the choice of fighting for the master race, or playing naked volleyball with chicks who had 60's style Russ Meyer breasts.

They "did the right thing . . . "

"just a century"?

[jeffb (2.718)]

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.

Re: "just a century"?

[bill_mcgonigle]

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.

Re:"just a century"?

[Chrontius]

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.

Inconceivable!

[Anonymous Coward]

... 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."

Re:From the wisdom of Sherlock Holmes...

[Jeremi]

"Sherlock Holmes observed that once you have eliminated the impossible then whatever remains, however improbable, must be the answer. I, however, do not like to eliminate the impossible."
- Douglas Adams, Dirk Gently's Holistic Detective Agency

What about the "hot pole" theory?

[Anonymous Coward]

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.

Re:What about the "hot pole" theory?

[D'Eyncourt]

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.

Re:ok.. Come on...

[Anonymous Coward]

> So right here, on planet Earth, the same types of people - scientists - are incapable of understanding how a large structure the size of the pyramids was built a couple thousand years ago..

There are lots of theories; there's no particular surprise that they were able to, but we don't know exactly how it was done because it was a long time ago and the Egyptian engineers didn't leave very good records. Nobody is going to be able to prove within a shadow of a doubt how it was done, but there are lots of plausible ways it could have been done.

https://en.wikipedia.org/wiki/Egyptian_pyramid_construction_techniques#Construction_method_hypotheses

This is old news

[Smiddi]

This happened over 1,400 years ago!!

perhaps we should consider the obvious.

[Gravis Zero]

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

Re:"Old" news

[stealth_finger]

I beg your pardon, but this is already old news. It has been relayed by other channels at least two days ago. If /. still want to pretend being news for nerds, they have to catch up and post news when they are news, not two days later.

This comment is old news. Seeing as slashdot isn't a news site it's always been like that, it has no writers or reporters. All it is, is some people that put up interesting articles from elsewhere and then we all bitch and moan about all kinds of things, sometimes the original article may get a mention or may not depending how it goes.