Fading star

Neil deGrasse Tyson, as usual, put it best: "Allow me to remind you what the 'U' in 'UFO' stands for.  It stands for 'unidentified.'  That means we don't know what it is.  Now, if you don't know what it is, that's where the conversation stops.  You don't then say it must be anything."

That's a lesson that could use reinforcement, because there is a regrettable tendency on the part of a lot of folks to jump from "this is strange and we don't understand it" to "this must be evidence of (fill in the blank: aliens, ghosts, telepathy, any of a number of cryptids, any of a number of gods)."  Science, on the other hand, is perfectly comfortable with not knowing the answer.  If you don't know the answer, you continue to look.

And continuing to look, after all, is what science is.

As an excellent example of this -- and an excellent example as well of the right attitude in science -- consider Phil Plait's article over at Slate entitled, "I'm Still Not Sayin' Aliens.  But This Star is Really Weird."  In it, he gives further consideration to the star KIC 8462852, now more euphoniously referred to as "Tabby's Star" after Tabetha Boyajian, the astronomer who led the team that discovered its odd behavior.  Tabby's Star has been in Skeptophilia before, back in October of 2015 when the news of its peculiarities became public.  This star shows dramatic and irregular fluctuations in brightness, which (to date) have not been convincingly explained.  The most popular explanation, at least amongst the astronomers, was that Tabby's Star was surrounded by a huge swarm of comets that periodically blocked the light from it, causing an apparent dimming.

Now, I'm not an astronomer myself, merely a star-watching dilettante, but that never sounded all that plausible to me.  Considering that a transit of Jupiter across the Sun would only cause a 1% dimming in brightness as observed from outside the Solar System, and the brightness fluctuations for Tabby's Star reach a mind-boggling 22%, that would have to be one big-ass comet swarm.  But as the other explanations I heard included aliens building a Dyson sphere around the star, I wasn't gonna call the comet swarm hypothesis far-fetched.

But it gets weirder.  Bradley Schaefer, an astronomer at Louisiana State University, has found that not only does the light from Tabby's Star get occluded by something, triggering an irregular rise and fall in brightness in the short term, it has on average dropped in brightness by 20% over the past 120 years!

Graph of the magnitude of KIC 8462852 as a function of time [Schaefer, 2016]

To quote Plait:

That’s … bizarre. Tabby’s Star is, by all appearances, a normal F-type star: hotter, slightly more massive, and bigger than our Sun.  These stars basically just sit there and steadily turn hydrogen into helium.  If they change, it’s usually on a timescale of millions of years, not centuries. Schaefer examined two other similar stars in the survey, and they remained constant in brightness over the same time period. 

The long-term fading isn’t constant, either.  There have been times where the star has dimmed quite a bit, then brightened up again in the following years. On average, the star is fading about 16 percent per century, but that’s hardly steady. 

So it appears Tabby’s Star dims and brightens again on all kinds of timescales: hours, days, weeks, even decades and centuries. 

Again. That’s bizarre. Nothing like this has ever been seen.

Plait emphasizes that he's not saying this is aliens, but adds, a tad reluctantly:

I’d be remiss if I didn’t note that this general fading is sort of what you’d expect if aliens were building a Dyson swarm.  As they construct more of the panels orbiting the star, they block more of its light bit by bit, so a distant observer sees the star fade over time.

He does, however, add the caveat that if this is an alien civilization building a Dyson sphere, they're working at a breakneck pace.  They'd have to generate and install panels with a total surface area of 750 billion square kilometers -- 1,500 times the surface area of the Earth -- in a little over a hundred years in order to have that effect.

So Tabby's star is a mystery.  Which means it's cool, and there are gonna be lots of astronomers and astrophysicists working to try to figure out what's going on.

And it also means that there is no room for saying "it must be aliens."  The bottom line is that we still don't know.  Which is exactly where you want to be in science.  To once again quote Tyson:  "People are always saying that scientists have to 'go back to the drawing board.'  As if we're just sitting there in our offices with our feet up, everything figured out.  No, in science you are always back at the drawing board.  If you're not back at the drawing board, you're not doing science."

Stellar anomaly

Given that my interests are pretty well known to my friends and family, whenever anything interesting happens on the Bigfoot, ghosts, or aliens scene, I'm sure to be sent the relevant links more than once.

This time it's aliens, with the discovery of an anomalous light-dimming pattern in a star with the euphonious and easy-to-remember name of KIC 8462852.   You probably know that light-dimming is one of the main ways that astrophysicists locate exoplanets -- if a telescope on Earth detects a periodic dimming of the light from a star, it is likely to mean that a planet is in transit across it, temporarily blocking its light.  From the period and the extent of the dimming, inferences can be made about the size of the planet and its distance from its home sun.

But this time scientists have found something odd, because whatever is causing the dimming of KIC 8462852 is not acting in a regular or predictable fashion.  And whatever it is seems to be large.  Even a Jupiter-sized planet only blocks 1% of a star's light.  This star is undergoing an irregular diminution of its light... of up to 22%!

[graph of light intensity over time, after Boyajian et al.]

The most mysterious thing about the phenomenon is its lack of periodicity.  At the moment, scientists simply don't know what this means.  And idle speculation, without a good model for what's going on, is not usually fruitful in science, so the astronomers and astrophysicists are being circumspect.  Here's what astronomer Phil Plait had to say:

The authors of the paper went to some trouble to eliminate obvious causes.  It’s not something in the telescope or the processing; the dips are real.  It’s not due to starspots (like sunspots, but on another star).  My first thought was some sort of planetary collision, like the impact that created the Moon out of the Earth billions of years ago; that would create a lot of debris and dust clouds.  These chunks and clouds orbiting the star would then cause a series of transits that could reproduce what’s seen.

Plait admits the downside of this idea, which is that dust and debris should emit infrared light as it's warmed by the star it surrounds, and we're not seeing that.  Others have suggested clouds of comets...  or an alien megastructure.

Seriously.  Years ago Freeman Dyson proposed that a sufficiently advanced civilization could disassemble planets to build a huge sphere around its star, thus capturing (and utilizing) virtually all of the star's emitted energy.  (Dyson spheres show up all the time in science fiction, most famously in the Star Trek: The Next Generation episode "Relics," and in Larry Niven's book Ringworld.)  A partially-constructed Dyson sphere, or one that had been damaged, might be expected to have the irregular light-dimming profile we're seeing in KIC 8462852.

But even the people who work at SETI (Search for Extraterrestrial Intelligence) are being cautious.  There are other possible explanations that have to be ruled out before we can say with any kind of confidence that we're looking at something other than a purely natural phenomenon.  Recall that the discovery of pulsars back in 1967 by Jocelyn Bell Burnell was at first thought to be evidence of an alien signaling device -- in fact, the first pulsars to be detected were nicknamed LGMs (Little Green Men).  Fairly quickly, of course, it was found that there was a completely natural explanation for the observation.

As Jason Wright, astronomer at Pennsylvania State University, put it, "We have to keep in mind Cochran's Command to Planet Hunters: Thou shalt not embarrass thyself and thy colleagues by claiming false planets."

But SETI, quite rightly, is already requesting radio telescope time to study the phenomenon.  If this is evidence of an intelligent alien civilization, there should be a way to support this with additional evidence.  Until then, it's premature to state with confidence that this is anything other than an unexplained stellar anomaly.

It hardly needs to be added that I would be beside myself if it turns out we are looking at extraterrestrial intelligence.  Finding evidence that we are not alone has been one of my dearest desires since I was a child, probably explaining why I have various posters in my classroom featuring aliens, including Fox Mulder's famous UFO poster from The X Files with the legend, "I Want to Believe."  But I, like Plait and Wright and Tabetha Boyajian, the astronomer who discovered the anomaly, want to move forward cautiously here.  There is a long list of weird observations that have at first been touted as evidence of aliens and other fringe-y claims, and have not borne up under additional study.  The best I can say at the moment is that this one looks hopeful -- and certainly deserving of intense further investigation.