We're talking about events that happened 1,400 years ago, is this correct?
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...)
[...] I do kind of lament the uselessness of the effort [...]From the article:QuoteThese limits correspond to isotropic radio transmitter powers of (4–7) 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".
These limits correspond to isotropic radio transmitter powers of (4–7) 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.
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.
Quote from: notsorandom on 12/05/2016 03:28 pmSending 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.
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?
Quote from: Vultur on 12/10/2016 01:58 amA 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.
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.
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.
Quote from: Star One on 12/10/2016 10:20 pmI 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/
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
There is a dwarf possibly in the system.
Quote from: Star One on 12/11/2016 08:25 amMods 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 QuoteThere 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 dateis just meant in the general sense that most stars have planets, so this one probably does too.QuoteThere is a dwarf possibly in the system.presumably refers to the previously identified M dwarf, which may or may not be associated.