The Story of Tabby’s Star: “The Most Mysterious Star in the Galaxy”

A couple years ago, a few amateur astronomers digging through a trove of Kepler data made a peculiar discovery: it was a misbehaving star in the constellation Cygnus; one which erratically dimmed in unpredictable and unprecedented ways. They flagged the star, which perplexed astronomer after astronomer and became a media sensation when whispers of Dyson spheres and alien technology began to circulate. Much of that hooplah has faded away now, as the star and its mysteries have largely been explained, but the story of KIC 8462852—colloquially known as Tabby’s Star—is one to remember.

The following is a transcript of the podcast episode.

In 1967 a team of PhD students at Cambridge University finished building a telescope. It was a radio telescope, meant to search for and research mysterious objects in the sky called quasars.

Quasars were a recently discovered phenomena at the time. Strange radio frequencies coming from space. The word “quasar” comes from “quasi-stellar” — kind of star-like. They looked like stars, but didn’t act like stars. For a brief time when they were discovered in the 1950s, people thought they were signals from aliens. The Byrds even wrote a songabout them.

Quasars didn’t turn out to actually be aliens of course. But they were still really mysterious. Scientists didn’t reach consensus about what quasars were until the 1980s. They turned out to be objects at the center of galaxies surrounding supermassive black holes. So in the 1960s quasars were still fresh, they had no idea what they were looking at. And that’s why those students at Cambridge were building the radio telescope: to look at quasars.

Radio telescopes don’t show an image like a regular backyard telescope. Instead, they look for radio frequencies, which show up as black scribbles on long sheets of chart paper. The Cambridge telescope produced 96 feet of these scribbles per day.

One of the PhD students who worked on the telescope was named Jocelyn Bell Burnell. It was her job to analyze those 96 feet of scribbles by hand. Late one night, Jocelyn came across what she called a bit of “scruff” in the data — an anomaly which appeared as a regular pulse, up and down every 1.33 seconds. It wasn’t a quasar. It was something else. It looked almost like a beacon, and it seemed to be coming from a single point in space.

Jocelyn and her team were perplexed. The signal looked man-made, but it couldn’t be. No star was known to behave like this. It wasn’t radio interference from Earth, that was ruled out. Yet it pulsed with perfect clock-like regularity.

There was, of course, the elephant in the room: what if this signal was made by somebody else? The team didn’t really believe they were seeing a signal from an alien civilization, but couldn’t prove that they weren’t. In an homage, they dubbed the object LGM-1 — the LGMstands for Little Green Men.

It wasn’t long before Jocelyn found a similar signal coming from a different patch of sky. And then another, and another, and another, begging the question: what are the odds that if this is ET, they’re showing up the same way in a bunch of places at once?

As you can guess, they weren’t looking at aliens. What they were looking at were fast-spinning, ultra-dense stars, like cosmic tops — a new class of astrophysical object. They called them pulsars, referring to the pulse of the signal, like a heartbeat — except, in this case, devoid of life.

The pulses Jocelyn detected in 1967 are often considered one of the most suggestive of an alien source ever detected.

Looking back, it’s difficult to understand that they had no idea what they were looking at. During that brief window in 1967, for all they knew, they could be gazing at the answer to one of life’s greatest questions — blinking at them from space in perfect, clock-like intervals.

In the time since her discovery, Jocelyn has become a highly respected astronomer. In a 1999 interview with NASA, Jocelyn was asked what surprises her most about the universe.

The uncertainty about astronomy. The surprises. They certainly do keep rolling in.

The reason I told you this story about the discovery of pulsars is because it closely echoes a story that’s unfolding right now in astronomy — the story of Tabby’s Star.

The star is named after Tabetha Boyajian, post-doctoral fellow at Yale University.

She first saw this star years ago.

But it’s not Tabby’s Star itself that’s peculiar. As far as stars go, it’s rather ordinary. What’s so perplexing is what’s around Tabby’s Star. There’s something there — orbiting — and we have no idea what it is.

If you follow space news, this story may sound familiar to you. It was big around the end of 2015.

Most of that hype came from an article published in The Atlantic called “The Most Mysterious Star in the Galaxy.”

This is the guy who wrote that article.

There could be many reasons why this story drew the attention it did, but there’s one clear reason above all others: someone said aliens.

We’ll get to that. But first, let’s rewind to a simpler time, before SNL and Late Night and the Atlantic article. Back when Tabby’s Star was simply another quiet, scintillating point of light hidden in the night sky.

Our story begins on March 7th, 2009, with the launch of a NASA mission called Kepler.

As the announcer guy said, Kepler’s mission was to find planets around other stars, called exoplanets. Kepler looked at over 150,000 stars in a section of space called the Kepler field, it’s a small square of space near the constellation Cygnus, and it measured their brightnesses for almost four years, looking for what astronomers call transits.

A transit causes a tiny dip in the apparent brightness of the star. Every few months we download all Kepler’s data and plot it out and end up with a light curve — that’s a measure of a star’s brightness over time.

This is where astronomers look for those transits. So every time a planet passes in front of a star, it gets just a bit dimmer, and that causes a dip.

Kepler collected over 150,000 light curves, including Tabby’s Star. Computers did most of the leg-work, they can look through and pretty reliably find these transits which indicate exoplanets, but there was still the chance they’d missed something. Remember when Jocelyn had to go through the 96 feet of chart paper by hand? That’s because humans are better at finding visual patterns than computers are. And that’s what we’re looking for here: recurring, small dips. Astronomers wanted human eyes to look through the data as well, just in case, so they reached out to the public — regular plebeians like you or me — to help classify Kepler light curves and find exoplanets. They called the program Planet Hunters.

This is Daryll LaCourse, he’s a Planet Hunter.

Now most of the light curves the Planet Hunters look through are normal, there’s nothing there, not even an exoplanet. Once in awhile if they’re really lucky, and this is rare, they’ll find recurring dips that indicate an exoplanet. It’s even rarer to find one the computers missed. But there’s one light curve among all the 150,000 that Kepler looked at, which is just totally unique. There’s nothing else like it. And that’s the light curve for Tabby’s star.

The light curve of Tabby’s Star is Exhibit A. It’s inexplicable. And it’s the crux of this story — the smoking gun.

In other words, totally ordinary.

The dips in the light curve are measured as a percentage of the light that they block out. Planets cause small dips, usually lasting a few hours. Jupiter, for example, would cause a dip of around 1%. What they find with Tabby’s Star are these massive dips — up to 20%, lasting for days and weeks, not hours.

There are two big dipping regions — one halfway through and one at the end.

It shot down in a sharp spike then gradually returned to normal.

Bizarre, and clearly not planets. Then, just as things are getting interesting —

Two of Kepler’s reaction wheels broke, which meant it couldn’t keep steady in orbit. Good news is, after some down time and a lot of head scratching, NASA and some genius engineers managed to salvage the mission and resurrect Kepler as K2, a new mission, a phoenix from the ashes.

Except, the catch:

Yeah, bummer. So Tabby’s Star has again slipped out of sight. Which sucks because it was just getting good — and also because Tabby and her team need more data. All we have are the four years of Kepler data, which raise more questions than they answer. Without more data, we’re in the dark.

I spoke with one of Tabby’s colleagues, Jason Wright, assistant professor of astronomy and astrophysics at Penn State. He and Tabby have been working closely together on trying to figure out this star. When I asked him what could be causing it, he broke it down for me:

The first idea, of course, is that there’s something wrong with the data.

That was ruled out pretty quick. They’ve exhausted all the obvious bad explanations by now: giant planet, it can’t be a giant planet.

Orbiting star?

Accretion disk?

Dust cloud?

Pulsations, starspots, polar spots, black hole discs — for various reasons none of these seem to cut it.

So far only one theory has stuck.

But Tabby still had a paper to write.

In her paper, she presents her findings and essentially concludes that we need more data to reach a conclusion.

There is one explanation, however unlikely, that Tabby didn’t mention in her paper. In serious astronomy it can be an icky topic, and also hard to prove.

This is an excerpt from Tabby’s TED Talk about the star.

Dyson spheres might sound like science fiction, but they fit the predicted path of what advanced civilizations might build. It’s possible.

Sound familiar?

But then came Tabby’s Star.

The whole dyson sphere hooplah is the reason this story attracted so much attention. Just search Google Images for “Tabby’s Star” and you’ll see what I mean.

The dyson sphere hypothesis is exciting to think about,

If you’re going to seriously consider extraterrestrial intelligence as a hypothesis, you have to see a signal. With this in mind, Jason reached out to an old colleague of his:

This is Andrew Siemion.

Jason and Andrew got to talking about this star as a potential SETI candidate.

The best telescope to use would be the Green Bank Radio Telescope in Virginia. It’s the Rolls Royce of radio telescopes. It’s huge, the biggest moveable land object in the world at over 100m in diameter, and it’s located in the United States National Radio Quiet Zone in Virginia, where radio frequencies are restricted to allow for good quality observations. So it’d be perfect, and they wrote up a proposal.

Despite hesitations, they submitted their proposal, and expect to begin observations in October of this year.

There are a number of ways to look for extraterrestrial life on other planets, depending how close we are. We can take samples or analyze the atmosphere for chemicals that suggest life (oxygen and methane are prime suspects). But most exoplanets are too far away for that, so we rely on SETI.

There are so many hypotheticals to consider when looking for alien life. We don’t know how it would manifest itself, how they’d behave — the whole idea of a dyson sphere is just that — an idea, a hypothetical, a concept. Really, who knows how aliens would behave, or what they’d build. What if they don’t follow the same rules of life as we do? And what if they don’t even use the kind of technology we’re looking for? You can’t rule it out. And that makes a bad hypothesis.

Bottom line is, if we have a hope of finding alien life, an interesting candidate — a mystery wrapped up in an enigma — we might as well try. Even if it takes an optimist.

I should mention here that an initial SETI survey in October 2015 came up empty. It doesn’t mean there’s nothing there — a follow-up survey with the Green Bank telescope will confirm that. And, again, even if they don’t find any signals, that won’t stop some people from persisting that this is a dyson sphere built by aliens — and that can’t be ruled out.

Okay, so quick recap: In 2009 Kepler launches to look for exoplanets around other stars. So it’s looking at all these stars, it finds one star exhibiting a strange light curve. Astronomers are stumped, there’s no known explanation, it’s completely unprecedented. Hypothetical alien megastructures come up as a possible explanation, and SETI is set to investigate.

But there’s one more thing. Just when this star seems as strange as it can get,

I called Dr. Schaefer up to talk about what he found. Just a heads up the audio quality isn’t too great here.

And so he ponders it for awhile, and then he thinks:

Fortunately, some astronomers began photographing the night sky over a century ago. The photographs are negatives preserved on glass plates,

The Harvard Collection contains photographs dating from 1890 to 1989.

So he thought:

So he goes to the Harvard archives and pulls out these photographs, and starts to do his thing.

And what he finds is astounding.

A recent follow-up corroborated Dr. Schaefer’s findings, showing that Tabby’s Star also dimmed by 3% in its overall magnitude over the course of Kepler’s four-year observation — so, again, this likely wasn’t a misread of the data. This is actually happening. Tabby’s Star is dimming.

Without more data it’s difficult to predict the next dip. So in order to solve the riddle of Tabby’s Star, we need more data.

It’s notoriously difficult and competitive to get any time on professional astronomical telescopes.

Tabby and Jason launched a Kickstarter campaign to fund continuous observation of the star by a private network of telescopes.

They surpassed their goal, which means that whenever the star goes into the next dip, it won’t do so in the dark.

We’ll have countless eyes on the star, ready to record what happens next, and hopefully, finally, shed some light on what’s going on.

Enigmas like Tabby’s Star, quasars, and pulsars remind us of the questions we don’t even know to ask, the unknown unknowns, the surprises. Inherent in science is a tantalizing uncertainty; that the knowledge we desire may perpetually remain just beyond reach — like a carrot on a string.

It’s fitting that Tabby’s Star is invisible to the naked eye. It forces is us to take a closer look, and reminds us that in the cosmos, not everything is as it seems. Behind the scintillating stars and shrouded in the darkness between are the surprises — the unknown unknowns — waiting to be discovered.

Now if you want to participate in real scientific research, go check out Planet Hunters at

Tabby’s Star was brought to the attention of astronomers by Planet Hunters, a number of whom are credited as co-authors on Tabby’s paper about the star — so it’s truly real science you’re contributing to. Quick shout out to a few Planet Hunters in particular who first flagged Tabby’s Star as strange: Andrew Szewczyk, Sam Goodman, and Abe Hoekstra.

If astronomy isn’t really your thing, there are lots of other projects you can participate in — arts, biology, climate science, history, medicine — all using the power of citizen science. One project I’ve been enjoying is Decoding the Civil War, transcribing real Civil War telegraphs. Go check them out —

This episode was produced independently by me, Asher Isbrucker.

I’d like to thank all of the people who gave their time and lent their voices for this episode: Tabetha Boyajian (@tsboyajian), Jason Wright (@Astro_Wright), Andrew Siemion, Brad Schaefer, Ross Andersen (@andersen), and Daryll LaCourse. Big thanks to all of you. Thanks as well to Professor Jaymie Matthews.

Music in this episode was by Lee Rosevere, Corsica S, Chris Zabriskie, Sergey Cheremisinov, Little Glass Men, Lee Maddeford, and Ketsa. You also heard excerpts from “CTA 102” by The Byrds, the X Files Theme, and the Late Show with Stephen Colbert.

If you want to follow dedicated news about the star updated by the team researching it, go to

Thanks, as well, to you — the listener. Whoever you are, thank you for lending me your ears. This is my second podcast episode and I’m still figuring this whole thing out — this episode was a tremendous challenge to put together, but I learned a lot in doing so. On to the next one.

Further information:

Planet Hunters credited with first flagging Tabby’s Star, setting this whole thing off: Andrew Szewczyk, Sam Goodman, and Abe Hoekstra.

Check out Planet Hunters & other citizen science projects

The official website for updates on Tabby’s Star

Tabby’s paper about the star

Ross’ Atlantic article about the star

And a follow up article

Tabby’s TED Talk about the star

Fact-checking Twitter account for Tabby’s Star



Writer & Video Producer.

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store