Andrew Masterson
Andrew Masterson is a former editor of Cosmos.
Tabby’s star, generally regarded as the weirdest star in the universe, just got even weirder. Or perhaps it didn’t. Perhaps it just became boring. It all depends on which research you read.
Tabby’s star, otherwise known as Boyajian’s star, or plain old KIC 8462852, is 1,280 light-years away in the constellation of Cygnus and has intrigued astronomers ever since a group of citizen scientists investigated data collected by the Kepler space telescope and found that its light fluctuated to a degree never before observed.
The star’s luminosity has been seen to dim temporarily but dramatically – up to 22% in one instance – prompting a slew of possible explanations that include the impact of a planet, a passing swarm of comets and even its enclosure by a hypothetical piece of alien mega-technology known as a Dyson sphere.
It gained its nickname after these variations were formally described in a 2015 paper, the lead author of which was Louisiana State University astronomer Tabetha Boyajian.
Now two new papers by astronomers analysing KIC 8462852 have surfaced, offering startlingly different interpretations. The first adds more data over a longer timeframe and finds the light fluctuations are even more pronounced than previously thought. The second suggests the periodic dimming is nothing more interesting than the product of a large cloud of space dust.
In the first paper, lodged on the preprint site Arxiv, a team led by Joshua Simon and Benjamin Shappee of the Carnegie Institution for Science in California analysed data from the All Sky Automated Survey for Supernova, covering about 800 days, and the related All Star Automated Survey, covering 4000 days.
The team found that between 2015 and mid-2017 Tabby’s star grew 1.5% fainter. However, the researchers also identified two previously unnoticed episodes during the past 11 years where the star actually brightened – an unexpected result.
:Up until this work, we had thought that the star’s changes in brightness were only occurring in one direction – dimming,” says Simon.
“The realisation that the star sometimes gets brighter in addition to periods of dimming is incompatible with most hypotheses to explain its weird behaviour.”
That does not, however, leave only theories involving alien technology in the frame. Indeed, a paper published in The Astrophysical Journal finds a plausible explanation that is a long way from the stuff of science fiction.
Tabby’s star dims, writes a team headed by Huan Meng of the University of Arizona, US, because of dust.
The team used data from NASA’s Swift and Spitzer space missions, along with information from the AstroLAB IRIS observatory in Belgium, and found something very interesting: the dimming of Tabby’s light wasn’t uniform across the spectrum. Instead, it was much more pronounced at the ultraviolet end than at the infrared end.
And that, concluded Meng and his colleagues, meant that if the light was being dimmed because something material was passing in front of it, that something must conform to some pretty definite physical constraints.
“This pretty much rules out the alien megastructure theory, as that could not explain the wavelength-dependent dimming,” says Meng.
“We suspect, instead, there is a cloud of dust orbiting the star with a roughly 700-day orbital period.”
The debris, Meng explained, cannot be the type known as “interstellar dust”, which is found in deep space, because its grains are so small that they would be pushed away by the pressure of Tabby’s starlight and could not remain in orbit. Particles known as “circumstellar dust”, however, are heavy enough to remain in orbit, but not, even when clumped into a cloud, solid enough to block light across the entire spectrum.
Meng acknowledges that other explanations may also fit the data, although not perhaps as elegantly, so it is unlikely that speculations about the strange behaviour of KIC 8462852 will be put to rest (especially with Simon and Shappee’s paper now in the mix).
However, it is now at least possible to suggest that all our dreams of finding evidence of extraterrestrial life have, for the moment at least, turned to dust.
