‘Tabby’s Star’ KIC 8462852 just dimmed to its greatest extent yet

USUALLY, the universe works as expected.

Planets and asteroids orbit like clockwork. Stars steadily change over the eons as they burn through their different types of fuels.

So when KIC 8462852 turned up in astronomical observations ‘flashing’ in an unpredictable, erratic way — eyebrows were raised.

It didn’t seem to fit any known stellar behaviour.

But it did fit with a 1960s prediction: that our first observation of an advanced alien species would be erratic light from a star being ‘harvested’ of its energy.

Dubbed ‘Tabby’s Star’ after the amateur astronomer who first brought it to the world’s attention, KIC 8462852 is being carefully watched for new clues.

And something’s just happened.

“This is the deepest dip we have observed since the Kepler Mission in 2013! WOW!!” researchers declared in a recent update on its behaviour.

GOING DARK

KIC 8462852 has darkened once again.

This time a shadow began to fall over its glow on March 16. It’s since dipped to the darkest its’ been since first observed by the Kepler Space Telescope in 2013.

Tabetha Boyajian of Louisiana State University reports this suddenly turned around on March 22, and it’s again increasing in brightness rapidly.

So what could cause a star to change its brightness by up to 25 per cent in just a few days?

The Dyson sphere idea at first seemed one of the most plausible.

It’s the notion that an energy-hungry advanced civilisation would need to encompass their star with solar panels to harvest the energy necessary for interstellar travel.

Naturally, such an enormous engineering pro ject would cast a shadow.

That shadow would likely not look at all natural.

Just like KIC 8462852’s erratic brightness.

But the idea is extraordinary.

It needs extraordinary evidence.

The star — a little bigger than our own — sits some 1500 lights years away.

SETI has scanned the system, and found nothing out of the ordinary.

And a swath of new theories offer plausible naturally occurring alternatives to the ‘megastructure’ hypothesis.

So have the Tabby’s Star aliens been killed off?

Astronomers have been sharpening their pencils, revisiting their calculations — and coming up with some new ideas to test.

STARLIGHT, WITH INTERMITTENT CLOUDS

In January, it was Boyajian and her colleagues that themselves put the final nail in the coffin of the ‘alien megastructure’ idea.

The team is operating through funding from a Kickstarter campaign. With the money, they were able to access observatory time and specialist equipment to sift through Kepler’s observations.

By now they’d observed several sudden shifts in KIC 8462852’s light.

This allowed them to analyse its spectrum — the bands of colour that make up its shine.

These bands offer a natural chemical analysis of the star’s composition — and that of anything the light passes through.

The light was revealing.

They found different types of light were blocked at different intensities.

“Dust is most likely the reason why the star’s light appears to dim and brighten,” Boyajian said in a statement. “The new data shows that different colours of light are being blocked at different intensities. Therefore, whatever is passing between us and the star is not opaque, as would be expected from a planet or alien megastructure.”

This leaves only one known possibility out of the process of elimination: very fine, powdery space dust.

MYSTERY SOUP

So the cause of KIC 8462852 strangely stuttering starlight appears to be dust.

But mystery remains.

Why isn’t it behaving in a predictable manner?

Why isn’t it orbiting in clouds subject to the same clockwork as planets, asteroids and comets?

Why is it so fine?

Where did it come from?

It’s not behaving in the way calculations predict ejecta would from collisions between asteroids or even large planets.

Nor does it match what would be expected from clouds of dust bundling around newly forming worlds.

At the moment the best idea is that the dust comes from a fractured remains of an enormous comet that had been orbiting the star every 700 days on a highly elliptical path. It’s the only idea that seems to fit the observation of KIC 8462852 slowly dimming before rapidly brightening again.

But it’s far from being proved.

“This latest research rules out alien megastructures, but it raises the probability of other phenomena being behind the dimming,” co-researcher Jason Wright wrote.

“There are models involving circumstellar material — like exocomets, which were Boyajian’s team’s original hypothesis — which seem to be consistent with the data we have. (But) some astronomers favour the idea that nothing is blocking the star — that it just gets dimmer on its own — and this also is consistent with (the) data.”