Frontiers in Artifact SETI: Waste Heat, Alien Megastructures & Tabbys Star - Jason Wright (ST 2016)

ah good afternoon ladies and ladies and gentlemen and welcome to you SETI Institute colloquium my name is Frank marches and a researcher at the SETI Institute and today I'm gonna be the host of d7 so let me first introduce our speaker Jason Wright dr. Jason Wright professor of astronomy and astrophysics at the Penn State University a graduate degrees is from University of California at Berkeley I graduated in 2006 so I should mention that we overlapped of over this time and finding each other for more than 10 years now so it's currently in this on the sabbatical spending time among the Center for exoplanets and abotobble words at Penn State serving as a visitor associate professor at the breakthrough listen laboratory at the University of California at Berkeley and is also occasionally with visitors here at the SETI Institute this primary research use precise Doppler measurements of nearby stars to discover and characterize the planetary system closest to the Sun on this side he also he had the G at you can explain what G at his of course search for extraterrestrial civilizations so I'll just mention the brief story three years ago I heard about Jason works on the search for caddy chef 2 & 3 civilization with weave wise another meeting from a telescope so I invited him to talk doing a hangout that we did with Jill tarter Matt Povich and Freeman Dyson and I think that was kind of an interesting hang out at the time because nobody really knew what what asked that astronomer was looking for Cathy chef to civilization so I recommend you watch this hangout again I did that yesterday and have two comments first of all we have younger looking girl and when we age gracefully okay so as the first comments the second comment is that a lot of happens recently in the search for k2 civilizations I mean the discussion is getting more and more interesting thanks to the discovery of the tabi stars so I think there was a great timing to have you back here and to talk about the new frontier in artifact SETI and the waste heat islands megastructures and tabby stars please join me in welcoming Jason thank you Frank it's good to be here I as Frank said there's a nice Google hangout with Freeman Dyson and Jill tarter and me and Matt Povich where we talked about a lot of this I also had an earlier SETI Institute science colloquium and so I kind of want to pick up where I left off with a lot of that the the SETI research I do is under an umbrella we call it G hat glimpsing heat from alien technologies and since I did that hangout in that previous talk come out with a bunch of papers explaining what we're doing and so I'll I'll quickly go over some of that and then we'll get into the most recent stuff that you may have seen in the news involving tabi star so our first paper motivates our search and explains what we're doing and how it's different from maybe traditional communication SETI so let me just start with something I've been saying in a lot of places and trying to try and emphasize what is SETI the search for extraterrestrial intelligence it's a lot of things it's researchers it's places it's it's it's things but most of all I think of it as a field of study it's related of course to astronomy and radio engineering and astrobiology but it's a field of study an interdisciplinary one and it has many components that complement each other the most famous component is of course Jodie Foster at the VLA from the film contact this is what most of us have in mind when we think about steady because it's the perhaps the most famous component of the search the philosophy behind this goes back to a classic paper in 1960 by cocconi and Morrison when they realized or you know published a paper arguing that it should be possible to communicate across interstellar distances with modern radio technology radio astronomy was just coming of age and in this paper they did the calculation and showed perhaps surprisingly that send signal with the technology we have today or had in the 60s to the nearest star that signal would be detectable with current technology if we had a comparable receiver at the nearby star and Frank Drake was also working along these lines at the same time so that line of communication SETI today has has many forms perhaps most famously the Allen telescope array which is operated by the City Institute to pursue that vision and search for signals radio signals from extraterrestrial civilizations across the galaxy and even beyond the the search though is largely funded privately the this whole field SETI gets very little if anything in the way of federal funding through the traditional ways that we fund science research and so it really relies on private philanthropy and people that are excited about it as with the Allen telescope array for instance but more most recently there was the 100 million dollar commitment by yuri milner to launch the breakthrough listen initiative and the breakthrough message initiative to really push communication study forward and and making a much bigger project than current than it currently was so this is now ongoing the Berkeley SETI Research Institute or Center is doing a lot of work to make this happen one of the places that this is being done is the Green Bank telescope operated by the National Radio Astronomy Observatory in West Virginia it's the largest steerable dish in the world and a great instrument for detecting extremely weak radio signal signatures from space the breakthrough this in project has purchased a large fraction of the time available on the telescope and has installed all sorts of cool hardware on the back end to improve its ability to detect signals from other stars so that's that's what we think of when we think of study a lot I'm not a radio engineer I'm not a radio astronomer but I was interested in helping with city project and so I don't build things like this and I was wondering what else what else can I do to contribute to the effort they turns out there's another strand of Seti that goes back also to 1962 a paper by Freeman Dyson he pointed out that if you have in a civilization it uses energy and if you have an old civilization and we think alien civilizations are very likely to be significantly older than us because we just got started in the galaxies billions of years old they might use a lot of power they might use significantly more power than we do many orders of magnitude more they might use a significant fraction of the available starlight to power whatever it is alien civilizations do and if they use that much energy we think about using energy but of course you never use up energy you have to conserve energy once it's done the useful work that you want it to do in your computer or whatever it is you then have to get rid of it and a higher entropy state and that's usually called waste heat so your computer does the work and your computer heats up and it radiates that energy away that it got out of the wall so energy is never used up it's just converted to higher entropy a lower temperature than it was when when you got it so you have this very hot star that's producing a lot of energy you collect it you use it and then you radiate it away at at lower temperatures longer wavelengths and it will usually come out in mid infrared radiation for most reasonable temperatures and so he said that if is this is a very general approach it doesn't matter whether they're intentionally signaling us it doesn't matter what they're doing if they're using huge amounts of energy that energy has to go somewhere when they're done with it that's bedrock thermodynamics and and so he suggested that we look for stars that have an excess of infrared radiation coming off of them that might be indicative essentially of the tailpipe of the civilization so where do you look for this how big could these civilizations be is that really practical in 1964 Nikolai Kardashev published a paper where he speculated how much energy could his civilization use he wanted to know you know they have a lot of energy available to them presumably this sets a limit on how powerful their radio transmissions might be that we might look for so he defined a type one civilization that could Harvard harness an entire planets energy supply all of the Starlight that falls on to the planet a type two civilization can harvest the entire stars output so you could imagine surrounding the star with a swarm of solar panels and a tag three civilization not only does that but also has interstellar travel and does so to all of the stars across an entire galaxy and so once you've harvested most of the stellar energy in an entire galaxy that would be a type three civilization and the timescales here are such that the time it would take a civilization to do such a thing by most measures is much smaller than the amount of time galaxies have been around and so there's no physical reason that we there couldn't be such civilizations throughout the universe spanning and you know collecting all the energy from whole stars collecting all the energy from whole galaxies so in the 1980s a satellite called iris was launched to map the entire sky at infrared wavelengths and one of these science outputs of that would be a search for stars that have infrared excess and perhaps looking for these type 2 civilizations this was complicated by the actual map which ended up looking like this revealing that the galaxy is filled with glowing dust at these infrared wavelengths this is the infrared Cirrus and that creates a background against which you're trying to see stars that might be giving up infrared light that made the this the satellite much less sensitive to to waste heat than people had hope and so it wasn't actually a very efficient way to go looking for so-called Dyson spheres or stars giving off a lot of infrared light we also learned that there are a lot of other kinds of stars that naturally give off infrared radiation further complicating this idea nonetheless one intrepid astronomer in particular Richard Kerrigan uh you'll see this was published in 2009 based on that 1983 satellite so this is really a hobby on the back burner for him for a long time he finally went through the entire catalog and checked out every bright star and studied it carefully too try and figure out if we had any good candidates in the data set and he found lots of sort of candidates upon further inspection he discovered that they're all things like carbon stars active galactic nuclei synthetic giant branch stars or h2 regions which are all very astrophysically interesting and so there's a lot of great science coming out of it but there was nothing that just said this is aliens around that star so that was that I think remains one of the only firm upper limits on how many of these civilizations exist in the galaxy so we can go a step up to galaxy spanning civilizations type three civilizations that was the only search I'm aware of to date before ours was also at Fermilab guy named James anise and he looked for galaxies that were too dim the idea is that if you surround the star with solar panels less light will get out than should so he wanted are there any galaxies out there that just are the surface brightness is too low you know the mass dynamically from how the stars move around the galaxies are there any that just don't have enough light because perhaps it's being blocked so he wasn't looking for mid infrared light coming out he was looking for a lack of optical light from stars coming out anyway he did the search in galaxies in the cluster and didn't find any strong candidates showing that there aren't any extreme cases of a type 3 civilization in that galaxy cluster so that's where we came in and I got thinking about this when we saw a talk at Penn State by a old friend of mine Mike Cushing who showed that the wise satellite which had recently published a lot of its data had discovered a brown dwarf with an effective temperature around 300 Kelvin so that means that the this is a failed star it's about the size of Jupiter but much more massive not as massive as a star so it's not fusing hydrogen and so it's only warm because it got put together when it was hot and it's been cooling off ever since then and it was basically a room-temperature object that wise had discovered in space and that's also about the temperature that humanity our civilization gives its waste energy off app which means that the wise satellite was sensitive to exactly the wavelengths that you might expect to find waste heat at and it also searched the entire sky and it did it more in a way that was much more sensitive than iris had so this was a new opportunity to try and improve on the iris upper limits so our strategy was to use that that data to go and see what we could find and we were able to do this through a grant that ultimately came from the John Templeton Foundation so again this is private philanthropy funding setting so um the one problem is if you just look for points of light that have lots of infrared radiation you don't know necessarily if it's a star right away wise detected 100 million sources and so going through all of those is is quite a challenge it will be easier in the future once we have more data to figure out what they all are but for now that was a bit daunting so we've restricted ourselves to looking for type three civilizations the way James and his head that is only looking at galaxies where you could actually see the whole galaxy in the image not just a distant galaxy that's a point of light because that could be almost anything so here's a here's an image of a nice spiral like our own this is the great galaxy in Andromeda and you see the dust lanes in the spiral arms that dust is actually glowing very brightly at mid infrared wavelengths and then the the soft glow everywhere that you see is just from a hundred billion stars all giving off their light so if we put on our infrared goggles and look at this so we'll switch over to a Spitzer image the same galaxy you see all of that dust that used to be dark is now bright and glowing in the infrared so this tells us a couple things it means just seeing infrared light from a galaxy isn't surprising dust does that but it also tells us that dust tends to be clumpy and if you look between the let the red lanes you can see regions of as hardly any dust coming out glowing at all if instead we had just seen a smooth distribution of infrared light that would mean that the infrared light was coming from the smooth distribution of stars not the clumpy distribution of dust and that would have been very interesting so by being able to resolve these galaxies we can distinguish cases that might be filled with alien civilizations versus ones that are bright because of dust I'm going to show one of these later so I just want to explain what it looks like this is a spectral energy distribution of a galaxy so the the black line and the red line goes on top of it towards the left represents how much energy in an old elliptical galaxy gives off one that essentially has no dust in it at all on the left you have optical light on the far right you have far infrared radiation and then right in the middle those those purple bands that go up and down those are the wavelengths that the wise satellite was sensitive to so the right-hand ones at around ten and twenty microns there's very little emission that you would expect to see from a galaxy with no dust at all but if just one percent of the Starlight were being intercepted from that galaxy and being used for some purpose and re-radiated at around 300 Kelvin it's not too sensitive to what temperature you pick there would be a significant excess of infrared light and so we wise would see that it was a little too bright and then if you have a galaxy that's filled with dust and star formation and is inherently very bright you'll get something like the green curve here this is a famous starburst galaxy called ARP 220 it's very bright at those infrared wavelengths at around 10 and 20 microns but even then it's not as bright as you would expect if 90% of the Starlight were being intercepted so what this means is that there's no natural source that looks like a galaxy where all of the 90 percent of the star lights being intercepted so that's our first upper limit if we can find anything with more infrared radiation coming out of it than that then that's an extreme beyond natural sort of thing and below that we're going to have to sort out we'll have to say these are the starburst galaxies these the dusty galaxies these are the ones that look strange and maybe we should investigate further sorry animation there okay so what we were basically trying to show is that there aren't any of these or there are these in the wise data set this is an image from wise the blue things are stars because of these wavelengths stars look very blue and the red thing in the middle is an extent little object it looks sort of galaxy shaped and it's pure red it's much brighter at red wavelengths than blue and that's the sort of extreme thing that we could easily find with our search when we looked through the database and in fact this was one of the best candidates that popped out of our search now it turns out this is a this is an artifact of the space craft there was a bright star at the previous pointing and it was sort of like getting a flashbulb in your face and you can see that flashbulb for you know a few seconds afterwards and that's what this is this is an echo of a previous pointing at a bright star but it shows that we would be sensitive to this and what we found is that we didn't see any of these and perhaps that's not too surprising but it's the first time anyone had shown that they are out there so we don't have galaxies that are all infrared emission and virtually no optical light escaping so our big paper with our results of that first search is that these sorts of galaxies that are mid infrared bright are very rare we looked at a hundred thousand galaxies we only had 50 that looked significantly infrared brighter than we would expect one of them was our 220 so that was a nice reality check they're all probably starburst galaxies like our 220 and indeed there was a follow-up paper by Michael Garrett who looked at what's called the mid infrared radio correlation and he showed that our sample of 50 falls just basically like you would expect comparing the green and the red essentially what you expect for starburst galaxies so they're almost all certainly starburst which is sort of what we knew but but this is the first big upper limit it's the first time some of this has looked for waste heat and we didn't expect to find anything right away because we're just learning how to do this I was when I was explaining this a friend pointed me to a referee comment on a famous paper by Davis in 1955 who would eventually don't want to discover neutrinos and they publish a paper looking for the solar neutrinos but their first attempts did not have the sensitivity required to detect them and the referee was not impressed by their first paper and wrote any experiments such as this which does not have the requisite activity really has no bearing on the question of the existence of neutrinos to illustrate my point one would not write a scientific paper describing an experiment in which an experimenter stood our mountain reached for the moon and concluded the moon was more than eight feet from the top of the mountain to which I reply if you have no idea how high the moon is that's a great first try I mean that only seems silly because you know the answer so you got to start somewhere and indeed you know you know you I'm sure that that people in antiquity tried exactly that to see if they could get any closer to the moon on a mountaintop and so this is just a first try but we can actually do much better we now that we know what we're doing we can better model that dust and look at galaxies in more detail and say yes that's because of dust we can get rid of that there are all sorts of contaminating sources that we had to sift through we have better ways to go and exclude those from the search and we can focus on sources where our sensitivity is high that is we can look at galaxies that we know don't have any dust elliptical galaxies measure their infrared output and there will be very sensitive because we know there's no dust and so we should hardly see any infrared radiation at all so anything we see will be interesting so that's where we were with our waste heat search when the the private philanthropic money ran out and so we're we're that's moving very slowly now but then another opportunity came up which would you might have heard about and I'm going to talk about next on a completely different angle we're not talking about type three civilizations before we go back to those those stars with too much heat that's the type two civilization on your way to a type two civilization though before you block ninety percent of a star light you block fifteen before that you block 10 before that you block one and so you know how would you notice if a star only had one percent coverage of the energy coming out of it from something that was on its way up and the answer is that sometimes the solar panels will pass in front of the star so this is a technique that we use to find planets orbiting other stars every time the planet goes in front of the star if the alignment is just right the star will appear to get slightly dimmer so first gaile if it's a planet the size of Jupiter around a star the size of the Sun the star gets about 1% dimmer which you can actually detect with high quality amateur equipment from the ground and many people have done that now that we know where to look and which stars have these planets the Kepler spacecraft was designed to detect things much smaller than planets the size of Jupiter but planets the size of Earth so it searched over a hundred fifty thousand stars in its prime mission of four years to see these planets passing in front of the star it was very sensitive to them before it launched though an astronomer named Luke Arnold published a intriguing paper in which he pointed out that you know it's not just planets that you will be sensitive to if there are huge swarms of solar panels if you have an alien civilization doing this if the panel passes in front of the star you'll see that too and he wanted to know could you distinguish a planet from a panel if the panel wasn't didn't have a circular aspect because why would they build it in the shape of a circle so not because they would do this but just to illustrate his point he said could you for instance tell the difference between a circle and a triangle so if an alien civilization had it for whatever reason triangular one would Kepler notice the difference these are both the size of Jupiter and so if you ask what this what this shape is this this characteristic shape that you see where it gets dimmer and then brighter again for a circle versus a triangle are they any different so he subtracted the two cases after calculating them and it's mostly the-- at those corners where there's a difference but yeah there would be a detectable difference which means for Jupiter sized objects Kepler could tell this thing is not round and planets have to be round more or less and so that would be interesting and suggested people look for that he also got very creative and said hey if they if they build these things why not build them in funny shapes that could send us information and so he imagined more complex structures with louvers that could signal us and flash us Morse code and things and give us very complex transit signatures as well and it's a neat idea that you might communicate information that way you might have the solar panels fly in formation to share an orbit which planets don't do and then you would see perhaps patterns of them go by and if they aligned them in certain ways that were obviously unnatural he said that would be a good way to communicate you know here we are we have solar panels arranged in prime number sequences in the same orbit this is ever there's no way you would mistake this for a planet is his point so if there are solar panels out there Kepler should be able to find them I said well that's a neat idea once Kepler finished its prime mission well did it see any and so we should be able to say these things aren't out there now that we have all this great Kepler data and so I went to write a paper about this ask all the different ways that these sorts of mega structures would be distinguished from planets and then ask what limit can we put on each of these different things that you might see so identified we artino identify ten possible anomalies that you might see around a star if it had these giant solar panels Luke Arnold had the first one that the shape of the transit would be different but it turns out there's a lot of different things you might expect he said you might have variable depths that is variable sizes as different sized objects passed in front of the star there might be many different panels and so it might not seem periodic the way that a planet does because you have lots of slow-moving panels in different orbits they also don't have a lot of mass probably and so it's possible that they experienced significant non gravitational acceleration that is just the pressure of the light striking there might be enough to alter their orbits and it turns out you can also tell that from light curves so and then there also might just be a swarm of them it could be it's not just one thing going around the star might be surrounded by a whole swarm of solar panels some bigger than others and when the big ones go by you might see that and it might be a very confusing complex light curve that you see and then we also suggested some ways that you could diagnose them and try and figure out what was going on now all of the things I listed there's a natural way that you could create that sort of signal and indeed many of these signals are seen in the Kepler data if a planet has rings then it's not a circle its aspect is non circular and so you should get a strange shape light curve if it has a massive moon like the mass of earth that will make it wobble which will throw off the timing and the moon itself will block the Starlight which will give you a strange transit curve and so we tried to think of all of the different ways that you could create these anomalies naturally which just goes to show that there's natural scientific reasons to go looking for them as well this isn't just a SETI search you go looking for these sorts of anomalies in the data set and you'll either discover aliens cool or you'll discover one of these other amazing things like EXO moons and rings and things like that so it's natural science as well as setting so um we wanted to put our upper limits on all of these but the point was that the really obvious stuff the Luke Arnold gigantic solar panels that would yes that's definitely not not a planet Kepler didn't see any of those or would have been all over the news right right well it turns out that there's a lot of Kepler data and the way that they go looking for the planets often involves algorithms because 150,000 stars four years of light curves it's just too much for one for people to with their eyeballs check everyone and say hey that's funny so most of the results you've heard about have come out of these automated pipelines that know what they're looking for and if they see something really strange they don't say hey what's this they say not a planet and throw it out so some regions of parameter space that turned out to have unexpected signals popped up this is kick 12:55 75 48 million own is kicked 12:55 obviously and check out this light curve so what you're seeing is the brightness of the star with time over the course of 15 days and every every day or so it gets about half a percent dimmer or sometimes 1% dimmer which is consistent with something like Jupiter going around it in an ultra short period orbit so it's orbiting about once a day but you'll notice the depths aren't constant and that's not resolution that that's real like it's variable depth and that's exactly what Luke Arnold said we should be looking for variable depths as different sized things in a common orbit go in front ah so that's kind of neat I feel like we should have got the citation there is like wow you thought that might happen and we saw it now not that this is aliens let's look a little closer at one of those dips by the way that's if you stack them all up and take an average that's the shape of the transit signature and that doesn't look like the nice flat bottom symmetric signal that you expect from a jupiter-sized planet so whatever's going in front every day or so doesn't have a circular aspect so bingo again there it is so what exactly are we looking at well the best model is that what we're looking at is an evaporating planet that is the planet is too small to actually block any light from the star but for some reason it's giving off huge amounts of material its evaporating because it's so close to the star we see more of these they all have very short periods so there's a common story here that if a rocky planet gets too close to the star it'll evaporate and the material coming off will form a dust trail and sometimes a lot of stuff is coming off and sometimes not very much is coming off and so the the the density of the tail is varies very rapidly and when it's dense you get a deep transit and when it's not dense you get a shallow transit and you always see first the the head come in and a quickly get darker and then even after the planets gone by that tail is still in front of the star so you get a soft fall off which is what explains explains this shape and there are a few other of these no now they're called ultra short period planets or evaporating planets so so that's neat those are there we have a natural confounder but there's cool science in it one of the things we did is we said well if this had been an alien signal it's possible there's information embedded in there Luke Arnold's idea was that this would be a way to communicate information bit by bit and so we asked so is there information in there and a grad student of mine Kimberly Cartier worked up a metric to try and determine how much information is in the signal like that just in case and we use this as a case to sort of see where it lands so the way it works is that all the way on the Left 0m that's there's no information and that's just a steady drumbeat that's like a pure carrier signal there's no information because it's exact the same every single time the only information you need to describe the depths is the depth because it's always that number all the way on the right one would represent pure white noise they're completely random transit depths and that would mean either you're dealing with some very stochastic process that behaves totally randomly or you're receiving highly compressed information either one and in between you can see where things land and so the B 1 and B 2 those are Luke Arnold's proposals for what these beacons might look like you can see that they are not at zero they contain a small amount of information just one two three five one two three five and kick 12:55 all the way on the right on the upper panel score is very high it's an almost random signal so is a neat a neat idea on a way to quantify this in both the time and the frequency domains so if we ever do see why don't we thinks aliens we can try and quantify how random it is but the lesson here is that the computer algorithms define these things are often throwing these out this required a lot of special analysis to find and find more like it so that's where the planet hunters come in you might be familiar with the planet hunters website it's a citizen science project at the Zooniverse where citizens any one citizen scientist can log in get an account and examine those hundred and fifty thousand light curves that Kepler produced for all of those stars and try and find the things that the automated algorithms missed because they don't look like we were expecting them to look so this is a real light curve of a real star the star got brighter over the course of 30 days that's that's probably an instrumental effect by the way not not really a getting brighter and looking to see if there's dips in there to identify by eye strange-looking things there was one in particular though that really got the planet hunters confused I mean they often found strange things and almost always turned out to be instrumental glitches or or something not all that interesting but there was one that really got them puzzled so here this is the actual talk page of one of the one of the stars and this is one of the users his handle is Nighthawk black explaining how he feels when he's trying to figure out what the heck he's looking at in this light curve so in the upper right you can see one the light curves it got dimmer and brighter that doesn't look anything like a planet transit and then here's another plot that shows an even stranger looking curve that doesn't look anything like a planet going in front either and so they contacted the the scientist the astronomer in charge of figuring out these anomalies and it took her a while to convince herself that it wasn't instrumental but but but real but once once it was determined to be real people got very interested so here are four different events the scale is different on all four of these the upper left is some of the first stuff that happened that got people confused you can see there's these sort of 0.2 to 1% dimming x' then around Kepler day 1206 on the upper right had this very complex shape and the one that really gets me is in the lower left over the course of a week it steadily got 15% dimmer now remember a Jupiter mass Jupiter sized object would make it one per centum so whatever's blocking the starlight is many times larger than Jupiter but it's this steady dimming dimming dimming and then suddenly it just snaps back to normal and I I don't know what that is then in the final quarter of what turned out to be the final quarter of Kepler's mission it just went crazy it's almost random and you can see you know long events short events deep events shallow events just all kinds of activity as the star gets dimmer and dimmer by anywhere from fractions of a percent to over 22 percent so the astronomer in charge of figuring this out dr. Tabitha Boyajian was working on this and trying to solve it for years and she had ruled everything out and at one point she showed me in my office and said what do you think this could be and I said I don't know but the paper I am writing where I said Kepler didn't see any of these is wrong ha ha like how many more of these are there like how would we know it took human eyeballs to identify these so I told her that we really need to get this out and talk about it and get more eyeballs on it to figure out what's going on and so even though she hadn't solved the mystery she she grudgingly published what she had so far which was a lot and it was actually the tenth paper by the planet hunters the second author there is Nighthawk black the the citizen scientist and here's the abstracts trying to understand what's going on and they needed to say something they needed to have some proposal for what it could be and so they concluded their highlighted that the scenario most consistent with the data is the passage of a family of EXO comment fragments all of which associated with a single previous breakup event so the idea is that each of those things are seeing is a massive comet much bigger than anything in the solar system with an enormous tale sort of like the evaporating planets except bigger and denser and that you don't just have one of these you have a whole family of them and each time one went by you saw the star get dimmer by sending Norma's amount it's very very clever and that's been the working hypothesis as to what it could be but it's it's it's very contrived because we don't know such comets exist we don't know why they would exist and it turns out it's going to have some other difficulties as well anyway they published this paper they made a minor media splash New Scientist picked it up around catching a cloud of comets orbiting a distant star and that's where things were but I still you know in the back of my mind well maybe it could be this is after all what Luke Arnold's more or less said we should look for it's what my paper said we should look for so I should probably put my time where my mouth is and we should go to the radio SETI people so we teamed up with Andrew Semien at the Berkeley City Research Center and he and dr. Boyajian and I submitted a proposal to the Green Bank telescope with the name the National Radio astronomical observatories and we asked for time to use the breakthrough initiatives back-end to look for radio communication because if they're harvesting lots of energy maybe they're using it to make radio waves so we submitted the proposal it was all very fun it's writing on my paper and then Andrew was testifying before Congress about astrobiology and while he was in Washington he met a reporter for The Atlantic named Ross Anderson and I knew something was brewing when I saw this tweet by Ross last night I had dinner with a director of Berkeley City Research Center we had a fun talk he wrote a neat little article on steady but one of the questions he asked Andrew was so are you guys looking at anything interesting do you have any hot leads and Henry said you know there's this star so Ross wrote another article the most mysterious star on the Gap star in the galaxy uh it's a great article I really like this article and right at the end he interviewed me about it and I really did give this quote it looked like the kind of thing you might expect an alien civilization to build note the hedge might expect not saying we found anything I'm saying it's worth looking because you need somewhere to look well it got a lot of attention here is one of the saner headlines that we got from BuzzFeed some places did well with it others not so well it was on The Late Show Neil deGrasse Tyson and Stephen Colbert and Seth MacFarlane all discussed the alien mega-structure star for the record Stephen Colbert's on Team mega-structure and Neil is on Team ordinary explanation we haven't thought of yet Seth Seth just chuckled and said he read it on BuzzFeed and that he think he said they think it's the Borg so it was an interesting study and how the media deals with this topic and I think it's one of the reasons it's hard to get one of the reasons it's hard to get government money is that it's hard to have a same conversation about it without you know BuzzFeed lighting it's hair on fire and everyone's saying we found aliens and so there were some interesting meta analyses why it's so hard for astronomers to discuss the possibility of alien life and I think it's one reason NASA is so careful to to make sure it's talking about discovery of you know microbial life or simple life forms and to start small and not jump all the way to the science fiction because then people start thinking about you know bumpy forehead aliens and bad acting and scripting and they just gets all silly and so it's hard it's hard to do this without stuff spinning out of control and so it's important to to to manage that um anyway that's not the end of the story we did it by the way.the we didn't get the telescope time at first but then BuzzFeed hit and the media attention came and everyone looked at the star and agreed yes this is really weird no you guys didn't make any mistakes and the second round we did get the time so October we're going to go down to Green Bank and see what we can do um and then then the star just got really weird Bradley Shafer is an astronomer at Louisiana State State University and he specializes in looking at these old photographic plates Harvard College Observatory used photographic plates for a hundred years to take pictures of a whole sky and there's this sort of lost art that some astronomers have have still have like bradlee of actually taking it's essentially a jeweler's loupe to these plates and by I measuring the magnitude of all the stars on these old plates so he went to Cambridge into the stacks and he pulled out the plates with a star in it and he measured the brightness of the star over the last hundred years and the the great points on this chart along the top are what a typical star does that's a Czech star of the same type from the same plate very nearby and Scot and then the blue points are averages of plate values across the century from 1890 to 1990 and how bright the star was and those are two lines suggesting more or less what the Stars been doing the the scales and magnitudes but the bottom line is basically 20% the star is almost twenty percent brighter or was in 1990 when they stopped doing the plates then it was in 1890 the star seems to have dimmed by twenty percent over a hundred years stars don't do that that is not a thing stars do and so he said this is the first thing other than the Kepler light curve that seems weird about what turned out the media grabbed onto the name tabby star after dr. Tabitha Boyajian well photographic plate photometry like this is difficult it takes a real expert like Bradley to do it right other people look at the plates and came to different conclusions the plates have all been digitized so you can actually access the data online at not quite full fidelity so it's a little harder that way and so there were a pair of papers first by Michael hit key and also by Michael luned the there were two papers by some mix of these people and they came to the opposite conclusion so the Loon paper said the that the kick eight four six two eight five two that is tabby star which we believe is consistent with constant flux over the duration of the observations essentially what they're saying is that the the quality of the photography is not good enough to make that kind of an assertion and then Michael hippety came to the same conclusion in the case of this star which has been claimed to dim by point one six magnitudes per century we show the trend cannot be considered as significant so this turned into a bit of a spat in public on blogs and things about who was writing who knew what they were doing and whether you could really say that and then even weirder and some astronomers uh actually that I know Benmont ed and Josh Simon said well you know if this thing really is getting dimmer shouldn't Kepler have noticed it get dimmer over its four years staring at it and the answer is that's really hard Kepler was not designed to do this kind of long term photometry it was designed to see short-term variations from planets passing in front of the stars so it only looked at a little part of the sky around every interesting star and as is the pointing moved around starlight would fall out of that little region it was measuring and fall in and so you get these trends in the photometry that are artificial instrumental and you can't tell really if a star's brighter at the end of the mission than it was before however it turns out every month Kepler took a calibration frame or just downloaded the entire sky as it saw it did that every month and those data should be good enough for that kind of measurement so they very cleverly took the so called full-frame images over the whole coupler mission learned how to do the photometry on them and measured how much stars get brighter or dimmer what they found is so everyone knows stars don't get brighter or dimmer over four-year timescales they stay the same that's just the way stars are and so they just plot it up all the stars that look like tabby star all the stars near tabby star and yeah the stars don't do that but there's this one outlier among all the stars they checked that got 3% dimmer over the whole mission and it was tabby star so here's their photography over 4 years of the mission the the points are their measurements from those once a month full-frame images and it goes from 1.0 one at the beginning down to 0.9 seven at the end so that's a 4% dimming of the star over that period and then the black curve is the the high frequency measurements and so the big vertical lines those are those dips I showed you earlier but now we're looking at all four years and so they're very narrow and you can't really see their shape so you can see all these little excursions down but there's also this very long-term trend that they picked out so the great curve is their best guess at the true light curve for this object combining long and short term photometry so tabby star faded throughout the Kepler mission and so this doesn't really confirm exactly what Bradley Shafer saw because this the plate stopped in 1990 and this all happened much more recently on the other hand they looked and they saw the same thing just at a different time so I think this strongly confirms Bradley Schafer's measurements and suggests that the star really is 20 or now 25% dimmer than it used to be and so at this point hypotheses like the Comets are starting to look even more contrived because why would comments over a century make the star dimmer what's going on so we're kind of all back at the drawing board at this point trying to figure something out and so we're also wondering like can megastructures do that is that what happens so some people have sort of so fishes facetiously offered that perhaps this is a Dyson Sphere under construction you're seeing lots of material getting built in just a hundred years they've blotted out 20% of the star light it seems kind of fast to me but you know no aliens right I think a more natural explanation if you wanted to invoke the alien mega-structure hypothesis it's just say that there's a swarm and those those those panels are in orbit around the star and some parts of the swarm are denser than other parts and if they're out orbiting at 10 astronomical units or 20 they move slowly and you'll slowly see denser parts of that swarm orbit into view and that would naturally make the star get brighter and dimmer as dense parts of the swarm came around so if I had to invoke megastructures to explain it that that that seems consistent you've got lots of panels of different shapes different sizes and the big ones make big dips and small ones make little dips and then the whole swarm is sort of like a translucent screen that makes the whole thing different that explanation the Comets and a lot of other explanations all are actually having a lot of trouble and that's because we go back to the waste heat anything it doesn't have to be a computer or solar panel or whatever it can just be dust anything that's around a star that intercepts the Starlight it's going to heat up and once it heats up it's got to give off infrared radiation and once it gives off infrared radiation we should be able to detect it and we don't this was not something that popped up when we looked at the Y's data set it did not have a lot of infrared radiation and in fact Thompson at all came out with a paper and they looked at millimeter radiation and they didn't see anything so this is the this is a spectral energy distribution like the ones I showed earlier the gray line there that's what we expect the star to have and sure enough on the left at optical wavelengths it's brightnesses those black dots are right where you expect the triangles on the right the four triangles are upper limits non detection zit cannot be brighter than this level because we don't see anything and so the first one on the green line that's at 20 microns that's from wise and then the three on the right are millimeter wavelength observations made with the submillimetre array and scuba - and the those curves represent how much you should expect if you have cold dust of certain amount and so they measure things in earth masses but for the purposes of this talk let me translate things into fractions of Starlite being absorbed so I've translated all these measurements into slightly different units here the black curve is what would happen if 20% of the Starlight like Bradley Schaffer measures was being collected by a swarm of stuff whether it's dust or solar panels or anything and it was all coming out at 65 Kelvin which is pretty cold if you make it colder that bump moves to the right a little if you make it warm where it moves to the left and that is ruled out by factor of 100 by those upper limits 20% of the Starlight is not being reprocessed into the thermal infrared or to the millimeter in fact the purple line is if only 0.2% of the star lights being reprocessed by anything and that's barely consistent with the curve so what this says is that whatever is blocking the Starlight it can't be isotropic it's not surrounding the whole star it must be along our line of sight so you could do that if it's in a disc of some kind and that hopefully will help constrain what the heck is going on but but I think it's it's almost a fatal blow against the idea that there's a spherical swarm of megastructures around it now the way out is that of course the alien civilization could be doing something with the observation with with the radiation that is it allowed under the laws of thermodynamics to use some fraction of the energy in a low entropy way and only dump the last bits out at high entropy so for ins but it keep it so what do you do with energy if you can't keep it if you don't re ready ate it away well I guess you could turn it into mass that's a low entropy way to do things but that seems hard it could radiate it away at low entropy as communication they could use it as car dash off originally proposed as radio so if that's right then then maybe there's something to hear with the radio waves so the Allen telescope array has already pointed at it and done a pretty deep stare and they had a nice the SETI Institute had a nice paper about their non detection of radio so when they looked at the frequencies they looked at the sensitivity they had they did not see there was no strong radio transmission coming out oh I should also mention if they were to do that at 20% the maximum efficiency they can have is 99 percent which means this is just barely at the edge of possibility according to thermodynamics if they're collecting 20% of the Starlight then of that 20% they're allowed to be amount 99% of it but the other 1% has to come out in the infrared and that's the Purple Line which is just barely consistent with what we have anyway so if that's what's going on and it's even even longer shot today than it was when we first proposed it I think then hopefully we'll be able to see something with the Green Bank telescope when we head out in October and get a nice big data set on it and while we're there I'm trying to see if we can also maybe look for stuff along the line of sight that might be able to explain what's going on so I'd say we have no good explanations right now for what's going on with tabi star we've been we've been sort of crossing off of our list of bad explanations more and more things as we get more data we still have a couple ideas working out of paper right now about what really could be going on but for now it's still it's still a mystery and I think the the one of the things that tabby star teaches us is about the value of this non-communication study and what it offers essentially artifact SETI we see something and we're really hard pressed to say it's not natural it's I mean without some kind of like prime numbers or something like that there's no reason to say it's just dust or you just haven't thought of the right thing yet communication said he looks for obviously intelligent signals but has to cast this impossibly wide net you don't know where to look you don't know when to look you don't know what frequencies to use it's just it's this huge sea of possibility and you're kind of going through as your tartar likes to say you know one glass at a time looking through this whole ocean so but that means these are complementary approaches the artifact SETI approach can find the anomalies and then hand them off to the communication city folks to enrich their target lists and give them better targets to look at then sort of pointing blindly so at least we know where to look and so I think together the two forms of Seti are pretty powerful and I'm glad to have contributed in that way and that's the that's the story of tabby star okay the flow he's open for questions let's start with you Harry um I was wondering if the waste heat could be of some you know a collector could be radiated in a certain direction and isotropically right so could you do non isotropic rear radiation it's less efficient to go non isotropic so you can't hit your maximum thermodynamic efficiency if you do that but there are good reasons to do it I mean our spacecraft preferentially radiates in certain directions to control torques and and and things like that so they could be radiating it away from our line of sight if it's an isotropic swarm there's no reason for them not to point it at us unless they're like hiding from us or something like that if it's a disc though then that would explain why we don't see any heat for one reason it's not isotropic they're only absorbing some of it and that gives you a natural direction out of the disk that they might have chosen so right if it's non isotropic that would lower the waste heat explanation so the upper limits we have only rule out I think the the isotropic swarm around the storm high so I have another question about tabi star which is if if we take the idea that the plate study the hundred-year plate study and this new study are accurate and it has been declining for a hundred and twenty five years we know we think we know what kind of star it is on what stage of life it is what's the upper limit for how bright it was before we started looking so this is complicated by the fact that we don't know the distance to this star we say it's is 500 light years away or something like that I remember having a parsecs way but but we are basing that on the assumption that it's not anymore extinguished than we already see so that's based on they something I think it works out based on the colors of the star you assume it's 35% dimmer than it would be if there was no intervening material and that's where we get that distance if in fact it's 80% dimmer than it's supposed to be then that would mean it actually is quite close so we're being fooled by its dimness into thinking it's more distant so it's degenerate with the distance without a distance we can't break that but if we had a distance then we would know the total amount of dimming going on that would also tell us what's doing the dimming because dust has a characteristic reddening it imposes and we have an upper limit from from that on how much of the dimming can be due to dust fortunately it's on the guy at target list and so Gaia will give us a distance if it's astrometric solution is clean just caveat any one's on the guy at Eamonn knows if it's clean I'd love to know if it's coming out anyway in just a few months they'll give us a distance and that could be very surprising or it could tell us that that yes it's all dust and that would be interesting as well 125 years is nothing in astronomical time right right that's right yeah it's very fast stars have characteristic time scales on which they can adjust their structure to new brightness levels that's millions of years and so anything happening in a hundred years is not just two you're slow Thermal adjustment time of a star you need something much faster so Jason just serendipitously did it turn out that there's any fast cadence data on tabi star for ingress and egress the kind of I don't think there's any short cadence data on it I'm afraid um there a lot of people wonder why we weren't throwing more resources at it during the Kepler mission why wait until after the data had stopped before looking at it intensely but you have to remember there's a lot of weird stuff in the raw Kepler data and it took tabi years to convince herself that this was a real anomaly um when JWST comes online are you anticipating any contribution it can make with due to the fact that such an excellent infrared Observatory is there anything I can contribute it is that you're expecting to definitely so JWST has sensitive spectrographs and cameras that work out to about here at 30 microns and so we'll be able to push these limits way down hopefully actually trace the sed of the star down that'll push down these upper limits much farther I haven't done the sensitivity calculation but for exactly the reason you say I'm sure it'll be much much better so you know do you know where these points come from especially the one at hundred and thousand between hundred and yeah they're from s there from scuba two and the SMA right so nobody observe it Weaver Sophia at the moment which has a bit of sensitivity a better sensitivity yeah then ah no don't hate about those two slides that show how much the star dimmed over four years and hundred years the four years was three percent if you take that to 25th power is gonna be certainly more than twenty percent yeah that's right so so um the original the original analysis by Bradley he didn't claim this was secular or monotonic the the data are really noisy and so you can find lots of imagining ways when perhaps that got brighter here it could be linear could not the data aren't of high enough quality to tell and then the mon Tet the and Simon analysis shows it's definitely not monotonic so it clearly has episodes where it gets much dimmer and it's possible it has episodes where brightens as well and then we just haven't seen those um what's your sense about the accuracy of looking at the film by a human being with his eyeballs because Herschel was a musician and had the sense of studying things through through the telescope with his eyeballs and being able to process data with his eyeballs in his brain right so I don't think it's not valuable at all to do this but do you subscribe the objections to this to the variability in the film technology or yeah that well so that's that's why this is an art you can't just look at them how black the dot is and turn it into a number and say that's how bright the star was what what Bradley does is he looks at other stars to check so he lets the plates themselves tell him how precise the plates are so that's what this Czech star is this gray series of dots at the top is just one of several other stars he monitored to see what the quality of the data were and all of his Czech stars had this nice steady thing now there's also issues like you know did they change the kind of plate they were using how does it depend on focus and it just it's decades of work with the plates that train you what you can trust in what you can so it comes down to whether you know you trust his expertise or not unfortunately so assuming that the anomaly and the brightness of the star is caused by a disc and for the sake of argument it's not you know by aliens what would uh what would a disk space explanation be for this century long dimming of the star I I don't have one god no no really I don't I I think I've all but abandoned circumstellar explanations and I think now we're gonna have to talk about bizarre structure in the interstellar medium and stuff like that which the interstellar medium folks will say sure there's tiny structure I was just talking to Carl Hylas at Berkeley he's like I'm surprised more stars don't do this but still this is a 1 in 300,000 object people have gone looking for more and it's the only one so so that also says you're allowed to invoke one really rare thing because it is a rare phenomenon so so that's where I am now then it must be something in the interstellar medium I think you just answered whoops can't ask you is it a very distant a you know procession of a very distant object or interstellar so yeah I think yeah remember the earth and Tavi star and the interstellar medium are all moving and so your line of sight through the interstellar medium moves at a significant rate like 30 kilometers a second an au per year or so so if there were strong density fluctuations in the is m in that direction it could sort of do it except that's not a thing stars do so anyway it's hard to make it work when you were talking about searching through the Kepler data for other possible a B star uh there's a company called Numenta that has a machine learning technique that's very good at anomaly detection cool and they should be able should be able to do this sort of stuff for free you know for free also I would hope that's a good price there are several Lucien welco which at the Adler Planetarium actually has been using nonparametric techniques that much I'm sure of to look through the data and look for anything unusual and not just for things like to have a store but certainly like that but just for things we didn't know that we were looking for and try and identify other ones and so I I think it's a great idea and I think we need more more techniques like that to find these anomalies okay thank you very much so before we clap please please let's wait for I'll take a picture of me or link giving you this amazing mug from the SETI Institute okay you had it last one two three years ago so but since you here in California keep this one this will be the Californian one cry stay here thank you thank you very much for this all right you you

Channel: SETI Institute

Views: 53,217

Rating: 4.7923875 out of 5

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Id: XEDR-G2EDRM

Length: 64min 5sec (3845 seconds)

Published: Fri Aug 12 2016

Reddit Comments

[u/MiguelMenendez]

I love this type of scientific lecture, where it ultimate conclusion is "We don't know, exactly."

[u/alllie]

That was interesting.

[u/PersonOfInternets]

Can someone repeat that title to me in english so I know if I want to watch this or not?