Author Topic: Boyajians Star Updates And Discussion  (Read 11069 times)

Offline M.E.T.

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Re: Boyajians Star Updates And Discussion
« Reply #20 on: 12/04/2016 10:10 PM »
We're talking about events that happened 1,400 years ago, is this correct?

That is correct.

Offline Johnnyhinbos

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Re: Boyajians Star Updates And Discussion
« Reply #21 on: 12/05/2016 01:30 AM »
So if there was a Dyson sphere being constructed some 1,400 years ago, wouldn't there be some much greater probability of seeing such a thing in our neighborhood some 1,400 years later?

(Queue the Fermi paradox comment...)

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Offline rocx

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Re: Boyajians Star Updates And Discussion
« Reply #22 on: 12/05/2016 07:03 AM »
So if there was a Dyson sphere being constructed some 1,400 years ago, wouldn't there be some much greater probability of seeing such a thing in our neighborhood some 1,400 years later?

(Queue the Fermi paradox comment...)

No, because travel to our neighbourhood would necessarily take longer than 1400 years.
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Online LouScheffer

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Re: Boyajians Star Updates And Discussion
« Reply #23 on: 12/05/2016 02:53 PM »
[...] I do kind of lament the uselessness of the effort [...]

From the article:
Quote
These limits correspond to isotropic radio transmitter powers of (47) 1015 W and 1019 W for the narrowband and moderate band observations. These can be compared with Earth's strongest transmitters, including the Arecibo Observatory's planetary radar (2 1013 W EIRP). Clearly, the energy demands for a detectable signal from KIC 8462852 are far higher than this terrestrial example (largely as a consequence of the distance of this star). On the other hand, these energy requirements could be very substantially reduced if the emissions were beamed in our direction.
So the observation rules out transmissions that greater than a petawatt or exawatt scale isotropic source.   There is no way to make any assessment of the ETI hypothesis from the observation, as a nullification or in support.  It just "is what it is".   
The key here is the very substantially reduced in the abstract.  If they know we are here, and might be listening, then the power requirements can be quite modest.  In fact. 1 watt (not a typo) would suffice.  They need to cover a disc of about 1 AU centered around our star.  That's a radius of 1.5e11 meters, or an area of about 7e22 m^2.  1 watt produces 1.3e-23 w/m^2, an intensity we can detect narrowband.  (To see this is indeed plausible, note that we can detect the carriers from spacecraft at Mars even when the are using their omni-directional antennas and just a few watts.  That's a similar intensity).

Now this would require a very big (by Earth standards) transmitting antenna (to make a 10^11 m spot from 10^19 meters away takes an antenna about 10^8 wavelengths across, or 3000 km at a 3 cm wavelength).   But there are other compromises, such as 10 kw from a 30 km size antenna, or 1 MW from a 3 km antenna (that's just a factor 6 bigger than Earth technology).  And if the antenna was a phased array, not a dish, they could send signals to all potential recipients in a half sphere simultaneously, so they do not have to be targetting just us.

Anyone who might send us a signal probably already knows there is a life-bearing planet in our system, since we are (on a historical scale) close to this technology already.  So assuming they wanted to send a signal, they could target just those, for a modest investment in power and technology.   So it's not useless to look.
 



Online notsorandom

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Re: Boyajians Star Updates And Discussion
« Reply #24 on: 12/05/2016 03:28 PM »
Sending a signal over a thousand light years means figuring out where the target will be over a thousand years from now. Even a small fraction of a meter per second unaccounted for in the prediction of the star's motion over a thousand year can throw the beam wildly off target.

Online LouScheffer

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Re: Boyajians Star Updates And Discussion
« Reply #25 on: 12/05/2016 04:10 PM »
Sending a signal over a thousand light years means figuring out where the target will be over a thousand years from now. Even a small fraction of a meter per second unaccounted for in the prediction of the star's motion over a thousand year can throw the beam wildly off target.
As above, they need an angular accuracy of about 1 part in 10^8, projected 1400 years out (actually about twice that, since the observer sees where they were 1400 years ago, and needs to predict where they will be 1400 years from now).  Gaia, in orbit now, is measuring positions to about 1 part in 10^10.  So if the mission lasts 30 years (or better yet, 2 Gaia-like missions 100 or more  years apart), your aiming data should be more than good enough.  So aiming is likely not the limiting factor.

Offline JasonAW3

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Re: Boyajians Star Updates And Discussion
« Reply #26 on: 12/05/2016 04:57 PM »

      I hate to bring this up, but if one is expecting possible communications from a nonterrestrial source, such as Tabby's Star, has anyone considered the possibility of modulated X-rays?

      NASA is currently studying this as a potential alternative to both RF and lasers.  Apparently, not only is there far less signal diffusion from an X-ray laser, rather than an optical laser, but due to the wavelength, far more data can be encoded into such a beam, and transmitted with far less signal loss from both distance and potential obscuring gas clouds.

      There's always been the speculation that if there is sapient life, other than ourselves, in space, that they might use something other than radio waves to communicate over vast distances.
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Online notsorandom

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Re: Boyajians Star Updates And Discussion
« Reply #27 on: 12/05/2016 06:47 PM »
Sending a signal over a thousand light years means figuring out where the target will be over a thousand years from now. Even a small fraction of a meter per second unaccounted for in the prediction of the star's motion over a thousand year can throw the beam wildly off target.
As above, they need an angular accuracy of about 1 part in 10^8, projected 1400 years out (actually about twice that, since the observer sees where they were 1400 years ago, and needs to predict where they will be 1400 years from now).  Gaia, in orbit now, is measuring positions to about 1 part in 10^10.  So if the mission lasts 30 years (or better yet, 2 Gaia-like missions 100 or more  years apart), your aiming data should be more than good enough.  So aiming is likely not the limiting factor.
How predictable are stellar motions throughout the galaxy over that timeframe? Over a long enough timeline small but unaccounted for perturbations make all orbits somewhat unpredictable.

Offline as58

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Re: Boyajians Star Updates And Discussion
« Reply #28 on: 12/05/2016 07:23 PM »
How predictable are stellar motions throughout the galaxy over that timeframe? Over a long enough timeline small but unaccounted for perturbations make all orbits somewhat unpredictable.

Even a few thousand years is a very short time when you are considering motion of stars in the Milky Way. I haven't done any calculations to back it up, but it seems to me that if you had the technology to build a sender with good enough directionality to make the proper motion of stars worth considering, you would also have the technology to measure the proper motion to high enough precision.

Offline Vultur

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Re: Boyajians Star Updates And Discussion
« Reply #29 on: 12/10/2016 01:58 AM »
A hypothetical civilization capable of building structures large enough to cause the Boyajian's star dimming events certainly could beam signals to us.

But we're really not that close, and there seem to be a lot of planets in the galaxy.

Any signal that we could receive now would have been sent 1400 years ago... and their information on Earth would be how it looked 2800 years ago, in the time of Homer in Greece and the Zhou Dynasty in China. So no radio signals from Earth, no evidence of industrial pollution in spectroscopy of Earth's atmosphere, no night side lights (even if they had super-interferometry telescopes good enough to see those).

So why would they pick Earth to send signals to? What would make them think there'd be a civilization here able to receive it?

Offline Johnnyhinbos

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Boyajians Star Updates And Discussion
« Reply #30 on: 12/10/2016 07:13 AM »
To get to the point of my earlier comment - that we are looking at a star 1,400 years in the past - and it is a bit nuanced, but in a nutshell - if a civilization had survived to the point of maturity to be able to build a Dyson sphere (aka a Type II civilization on the Kardashev scale) some 1,400 years ago, then in our existence, 1,400 years later, the galaxy should be filled with intelligent radiation. Since it's not then it's doubtful that said civilization ever got to such a point in the first place.

Numerically speaking, think of the Carter catastrophe, and apply it to the Fermi paradox.

Therefore, sadly, I highly doubt the dimming events are caused by another civilization.
« Last Edit: 12/10/2016 07:18 AM by Johnnyhinbos »
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Offline JH

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Re: Boyajians Star Updates And Discussion
« Reply #31 on: 12/10/2016 07:53 AM »
Your conclusion suffers from the same problem as all applications of the German tank problem to civilizational survival: rigid application of statistics with incomplete knowledge of constraints. How do you know that the aliens in question aren't just homebodies?

To be clear, I think a natural explanation for the dimmings of Boyajian's star is much more likely than aliens.

- typo
« Last Edit: 12/10/2016 07:54 AM by JH »

Online LouScheffer

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Re: Boyajians Star Updates And Discussion
« Reply #32 on: 12/10/2016 06:36 PM »
A hypothetical civilization capable of building structures large enough to cause the Boyajian's star dimming events certainly could beam signals to us.

But we're really not that close, and there seem to be a lot of planets in the galaxy.

Any signal that we could receive now would have been sent 1400 years ago... and their information on Earth would be how it looked 2800 years ago, in the time of Homer in Greece and the Zhou Dynasty in China. So no radio signals from Earth, no evidence of industrial pollution in spectroscopy of Earth's atmosphere, no night side lights (even if they had super-interferometry telescopes good enough to see those).

So why would they pick Earth to send signals to? What would make them think there'd be a civilization here able to receive it?
In this situation, one possibility is that Earth gets no special treatment - they send signals in the direction of all life-bearing planets they know about.  If they can build Dyson spheres, they probably know the Earth exists, and has at least a good chance of having life.  They would know, for example, that oxygen and methane co-exist in our atmosphere.  Since these react on a short time scale, that means there is an active source of each.  I don't think we know of any non-life explanation for this.

The technology to send signals to multiple planets simultaneously is straightforward using phased array antennas.  Using existing Earth technology, we could send signals that we ourselves could detect to all the planets we have discovered so far, if we wanted to (See Appendix B of the book "SETI 2020" for several ways this might be done.)   Aliens presumably know of more planets, but can build larger sending arrays to compensate.  The power requirements are modest since the beams are highly directional.

The main advantage of this strategy is that communication does not depend on long lifetimes for technical civilizations.  If they wait until they see we have technology, then even if they reply right away, then we won't know of them for at least 2800 years after technology development.  If they signal in advance, we could find it after only a few decades of technology, and might even reply.  Depending on what we chose to send, they could find out quite a bit about us even if the lifetime of our civilization is short.



Offline M.E.T.

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Re: Boyajians Star Updates And Discussion
« Reply #33 on: 12/10/2016 07:14 PM »
A hypothetical civilization capable of building structures large enough to cause the Boyajian's star dimming events certainly could beam signals to us.

But we're really not that close, and there seem to be a lot of planets in the galaxy.

Any signal that we could receive now would have been sent 1400 years ago... and their information on Earth would be how it looked 2800 years ago, in the time of Homer in Greece and the Zhou Dynasty in China. So no radio signals from Earth, no evidence of industrial pollution in spectroscopy of Earth's atmosphere, no night side lights (even if they had super-interferometry telescopes good enough to see those).

So why would they pick Earth to send signals to? What would make them think there'd be a civilization here able to receive it?
In this situation, one possibility is that Earth gets no special treatment - they send signals in the direction of all life-bearing planets they know about.  If they can build Dyson spheres, they probably know the Earth exists, and has at least a good chance of having life.  They would know, for example, that oxygen and methane co-exist in our atmosphere.  Since these react on a short time scale, that means there is an active source of each.  I don't think we know of any non-life explanation for this.

The technology to send signals to multiple planets simultaneously is straightforward using phased array antennas.  Using existing Earth technology, we could send signals that we ourselves could detect to all the planets we have discovered so far, if we wanted to (See Appendix B of the book "SETI 2020" for several ways this might be done.)   Aliens presumably know of more planets, but can build larger sending arrays to compensate.  The power requirements are modest since the beams are highly directional.

The main advantage of this strategy is that communication does not depend on long lifetimes for technical civilizations.  If they wait until they see we have technology, then even if they reply right away, then we won't know of them for at least 2800 years after technology development.  If they signal in advance, we could find it after only a few decades of technology, and might even reply.  Depending on what we chose to send, they could find out quite a bit about us even if the lifetime of our civilization is short.

This of course leaves out the "why" question. As in why they would want to send all these signals out. Maybe they're as smart as Stephen Hawking, and realise that it is kind of a dangerous thing to do. Rather finish your "Death Star' device as much as possible before announcing your existence to the Universe.

Online LouScheffer

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Re: Boyajians Star Updates And Discussion
« Reply #34 on: 12/10/2016 07:58 PM »

This of course leaves out the "why" question.
They *why* part is really hard.  Imagine asking someone who lived 2800 years ago why we do all the various stuff we do today.  And that's the same civilization, on the same planet, with the same biology.  Add in different planet, different civilization, different biology, and potentially millions of years of development, and every conclusion needs to be treated as a guess.
Quote
Maybe they're as smart as Stephen Hawking, and realise that it is kind of a dangerous thing to do. Rather finish your "Death Star' device as much as possible before announcing your existence to the Universe.
Alternatively, it's perhaps more likely that anyone who is capable of coming here and beating us up, already knows (or will know, subject to the speed of light) about us whether we signal or not.  In that case it's better to make friends, see if they have any suggestions, and spread what we know.

Any conclusion that depends on the motivation of aliens is in very murky territory.

Offline Star One

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Boyajians Star Updates And Discussion
« Reply #35 on: 12/10/2016 10:20 PM »
I was reading a little while back that there may have been indications of planets orbiting this star but nothing terribly definitive as they probably aren't transiting from our prospective. There apparently was an indication of a brown dwarf.
« Last Edit: 12/10/2016 10:21 PM by Star One »

Offline hop

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Re: Boyajians Star Updates And Discussion
« Reply #36 on: 12/11/2016 06:15 AM »
I was reading a little while back that there may have been indications of planets orbiting this star but nothing terribly definitive as they probably aren't transiting from our prospective. There apparently was an indication of a brown dwarf.
Source? I haven't seen anything like that, and it should be big news if there is any serious evidence. Not clear what kind of evidence that could be based on either, I guess a BD or giant planet could be picked up in radial velocity.

Offline Star One

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Re: Boyajians Star Updates And Discussion
« Reply #37 on: 12/11/2016 08:25 AM »
I was reading a little while back that there may have been indications of planets orbiting this star but nothing terribly definitive as they probably aren't transiting from our prospective. There apparently was an indication of a brown dwarf.
Source? I haven't seen anything like that, and it should be big news if there is any serious evidence. Not clear what kind of evidence that could be based on either, I guess a BD or giant planet could be picked up in radial velocity.

Mods on the relevant Reddit who I believe some of which are professional astronomers.

https://m.reddit.com/r/KIC8462852/comments/5he29u/orbiting_planets_around_kic8462852/

Offline hop

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Re: Boyajians Star Updates And Discussion
« Reply #38 on: 12/11/2016 08:43 AM »
Mods on the relevant Reddit who I believe some of which are professional astronomers.

https://m.reddit.com/r/KIC8462852/comments/5he29u/orbiting_planets_around_kic8462852/
Thanks. I suspect that that
Quote
There probably are planets, but they aren't transiting (no surprise), and they are too small or too inclined to make a dent in the radial velocity measurements we have to date
is just meant in the general sense that most stars have planets, so this one probably does too.

Quote
There is a dwarf possibly in the system.
presumably refers to the previously identified M dwarf, which may or may not be associated.

Offline Star One

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Re: Boyajians Star Updates And Discussion
« Reply #39 on: 12/11/2016 02:24 PM »
Mods on the relevant Reddit who I believe some of which are professional astronomers.

https://m.reddit.com/r/KIC8462852/comments/5he29u/orbiting_planets_around_kic8462852/
Thanks. I suspect that that
Quote
There probably are planets, but they aren't transiting (no surprise), and they are too small or too inclined to make a dent in the radial velocity measurements we have to date
is just meant in the general sense that most stars have planets, so this one probably does too.

Quote
There is a dwarf possibly in the system.
presumably refers to the previously identified M dwarf, which may or may not be associated.

Will Gaia observations be able to confirm if it is associated or not?