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Thursday, 4 August 2016

Things that might be due to aliens, part 4: Tabby's star....

When we talk about the idea of finding alien life – whether that’s a galactic empire or a single microbe – people often get frustrated by the prevarications and grey-area language scientist use. There’s a good reason for that though: Every time a mistaken or false claim gets into the papers it damages the reputation of all scientists. 

So making a claim as big as first contact, only to have someone else prove you wrong, can end a career. That means research into anything remotely connected to the idea of alien life gets super, super, cautious. But there are a few odd, unsolved, mysteries in space that researchers will admit might – just might as an outside chance – turn out to be alien in origin. In the last post looking at the four most tantalising of these we'll be talking about...

Tabby's Star:

If you follow this blog, or have interest in astronomy at all, this mystery has probably crossed your radar at some point: Informally named for Tabetha S. Boyajian, the lead author of the paper that first drew it to world wide attention, this stars real full name is KIC 8462852 – and it’s still just possible that hideous string of alphanumeric gibberish will go down as the most important in human history. 

Just - it's looking shaky but the jury's still out.

The star first came to attention as part of an exoplanet hunt carried out by the Kepler space telescope. Kepler spots possible exoplanets by looking for the way a stars light dips as a planet passes in front of it. But when it looked at Tabby's star... things went a bit wrong:... 

This is the mystery: If you graph the light output of a star as a planet passes in front of it you’ll get a signature something like this:

That signature will repeat regularly, as the planet goes around it’s star – and although some exoplanets have been directly imaged by powerful telescopes, this is still one of the best methods for picking up the majority of exoplanets - they're mostly too close to their stars or too faint to image. 

Above: Images of  extrasolar planets - rare, and usually not showing more than a faint spot of light.

However, when Kepler looked at Tabby’s star, it saw a pattern of dimming like this: 

The dips in the stars brightness don’t follow any predictable pattern, and are so deep that something much bigger than a planet must be causing them. Instrumental error, the star itself somehow dimming and dust from planetary collisions were all ruled out. A swarm of disintegrating comets was proposed to be the cause, but this too would need special pleading (i.e. it’s incredibly unlikely to happen in such a way as to cause this dimming)... 

...And so, we get to that explanation, a very out there one but which was too exciting to ignore completely: Tabby’s star could be home to a heavily industrialised civilisation that was building a ‘Dyson swarm’. 

I'm fairly sure you'll have met this meme at some point....

A Dyson swarm is a huge cloud of solar energy collectors, which encircle a star and convert a huge chunk of it’s light output into usable power. Although the scale of such a project is totally beyond humanity today, the science and engineering principles are not – space platforms that turn sunlight from space into major amounts of useable electricity have been seriously proposed for decades. 

What made things even more exciting was that further investigation suggested that Tabby’s star had been steadily dimming for the last hundred years – exactly what you’d expect if a Dyson swarm were being constructed around it . That claim has been seriously questioned, and it looks like the apparent dimming is down to changes in telescope technology and observing methods.

SETI has also tried to tune into any possible radio or microwave transmissions coming from this solar system – and found nothing. If there were a huge construction project going on near the star you might expect to pick up some sort of chatter.... although our radio technology is only sensitive enough to rule out a very loud radio chatter (the star is 1500 light years away after all). 

Above: The Atacama Large Millimeter Array (ALMA)..

Debunking the long term dimming, and finding no clear radio signals, may weaken the case for the dips in Tabby’s star’s output being artificial but they don’t rule it out – the only way to do that is to actually come up with a plausible natural explanation for the dips, and prove it. So, if you fancy a challenge….

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