This illustration shows a star behind a shattered comet. Photo / Nasa
This illustration shows a star behind a shattered comet. Photo / Nasa
They're back! Speculation that a strangely pulsing star may have unnatural origins flared in 2015. Now a new survey has revealed it's not alone. And they're all oddly clustered together.
The star is designated KIC 8462852.
It's a yellow-white dwarf star sitting around 1470 light-years away.
It was given thenickname Boyajian's Star (Tabby's Star) or the "WTF Star" after astronomer Tabetha Boyajian discovered its odd behaviour. Its brightness varied by an unprecedented 22 per cent. Even more startling was the speed and randomness of its flickering.
How a star could pulse in such an erratic, dramatic way remains a mystery.
In 1960, astronomer Freeman Dyson published a paper "Search for Artificial Stellar Sources of Infrared Radiation". In it, he proposed the energy needs of advanced civilisations would become so great that it would need to cover its entire star with solar panels.
And the construction of such a "Dyson sphere megastructure" could be observed from Earth.
It's a controversial idea.
Many alternative ideas for the odd behaviour of Tabby's Star have been presented.
But none are without some flaw.
Now, a new astronomical paper published on the prepublication science site Arxiv.org says KIC 8462852 is not alone.
In fact, it may be just one of a tight cluster of some 15 stars that show the same bewildering changes in brightness.
Tabby's Star (Illustration) showing potential interaction between comets and dust clouds to cause the star's weird changes in brightness. Photo / Nasa
And, usually, the more weird somethings one finds, the less strange it becomes.
But not in this case.
More flickering stars have been found. But they're all in the same region of the galaxy.
"Fifteen new candidates with low rates of dipping, referred to as "slow dippers", have been identified," writes astronomer Edward Schmidt. "The dippers occupy a limited region of the HR diagram (star chart) and an apparent clustering in space is found. This latter feature suggests that these stars are attractive targets for Seti searches."
Schmidt says he sought to understand Tabby's Star by finding others displaying the same odd behaviour.
"It is difficult to gain an understanding of an astrophysical phenomenon with only a single example," he writes.
The 15 candidates he found are F and G type stars. Our Sun is a G-type.
Neither is supposed to be unstable.
And to find a clump of such oddly behaving stars is … odd.
"Since no fully satisfactory explanation for the behaviour of Boyajian's star, and by extension the Dipper candidates, has been found, it is premature to try to explain the existence of the clump," Schmidt writes. "However, the possibility that extraterrestrial civilisations might have developed interstellar travel and expanded beyond their original planetary systems has been widely discussed in connection with the search for extraterrestrial intelligence".
From the computer game "Dyson sphere Program". A Dyson sphere is an alien megastructure, built to harness the entire power output of a star.
Tabby's star was recently discovered to have a binary companion – another star in its orbit.
But that's not unusual.
And planets, when they pass between us and a star of this type, usually only cause dimming of about one per cent. Not the 22 per cent seen with KIC 8462852.
Not to mention their orbits, once observed over time, are predictable.
Another oddity is that the star doesn't dim equally across the entire spectrum. Instead, some wavelengths of light and heat are blocked more than others.
So whatever is causing the erratic dimming isn't entirely solid.
That would suggest vast dust clouds from obliterated planets or comets. But this would have to involve several overlapping clouds in eccentric orbits to explain the star's erratic pulsing.
A recent study found that a companion star, such as the red dwarf orbiting Tabby's Star, could help stir up such a dust storm.
"The binary companion may influence the long-term evolution of the system," it reads.
But doubt applies even here.
The red dwarf is unusually distant from KIC 8462852. It may be a binary. Some interstellar cataclysm may have also ejected it. Or both stars may be part of a moving group.
"With these considerations in mind, I suggest that the dippers in the clump and other stars in the same region would be appropriate targets for Seti searches," concludes Schmidt.
