As mysterious star that erratically dims by nearly a quarter as a swarm of unknown objects passes in front of it – leading to speculations that artificial objects could be orbiting the star – continues to refuse to give up its secrets after a search for laser pulses from the system turned up empty.
The star, nicknamed Tabby’s Star after Tabetha Boyajian of Yale University who first spotted its bizarre behaviour, hit the headlines in October 2015, sparking a variety of ideas as to what could be causing the odd dimming
Kepler discovers exoplanets by looking for them transiting – passing in front of – their star, but even the largest planets only block one or two percent of a star’s light. On the other hand, up to 22 percent of the light from Tabby’s Star is being blocked. The way the star dims implicates a cloud of objects and Boyajian’s favoured explanation is a cloud of cometary fragments after a large comet broke up.
However, the mysterious nature of the star, which is also referred to as KIC 8462852, has led to more speculative explanations. Jason Wright, a Professor of Astrophysics of Penn State University, has suggested that the swarm could be an extraterrestrial megastructure, somewhat similar to a Dyson sphere. Astronomers participating in SETI, the Search for Extraterrestrial Intelligence, have been looking for stars that look very similar to Tabby’s Star.
The SETI Institute’s Allen Telescope Array in California has attempted to detect deliberate radio signals directed our way from Tabby’s Star but has heard nothing. Now, a follow-up search for laser signals by astronomers using a 0.5-metre Newtonian telescope at the Boquete Optical SETI Observatory in Panama has also found nothing. High-powered lasers in the petawatt class and above are thought to be ideal for transmitting across interstellar distances– their shorter wavelengths and tightly collimated beams mean they do not disperse as much as radio waves, and a message sent be laser would have a much higher bit rate.
The distance of 1,480 light years to Tabby’s Star created some complications for the optical SETI search. Being so far away, any signals would be weak. Ordinarily, optical SETI experiments would split the light into two beams. Only if a laser pulse is detected in both beams would a detection be confirmed (this avoids false positives caused by cosmic ray strikes on the photometer). However at Boquete, the observatory’s director Marlin Schuetz uses a single photometer so as not to split what would already be a weak signal, before analysing the light to look for periodic pulses that could not be replicated by noise in the system.
In September of 2015, the star KIC 8462852 (aka. Tabby’s Star) captured the world’s attention when it was found to be experiencing a mysterious drop in brightness. In the years since then, multiple studies have been conducted that have tried to offer a natural explanation for this behavior – and even an unnatural one (i.e. the “alien megastructure” theory). At the same time, multiple observatories have been tracking the star regularly for further dimming.
Unfortunately, after years of excitement and speculation, the scientific community may have finally driven a nail into this theory’s coffin. According to a new study by a team of over 100 astronomers, and led by Assistant Professor Tabetha Boyajian – who made the original discovery – it now appears likely that KIC 8462852 (aka. “Tabby’s Star”) is being partially obscured by dust and not – I repeat, NOT – an alien megastructure.
What they found was that the dimming pattern was most likely caused by a cloud of obscuring dust around the star, as evidenced by the way light coming from the star being unevenly blocked.
The theory that KIC 8462852 might be surrounded by an obscuring dust cloud is not entirely new. In fact, a circumstellar debris disk was one of several theories offered in the past two years for the star’s mysterious dimming patterns. Other suggestions included shattered comets or asteroids, the presence of a giant planet, a planet with rings, or even a planet that had been consumed in the past.
Meanwhile, the dips that bore the name of lost cities were a reference to the activity (also ancient by human standards) astronomers have been observing from this distant star. “They’re ancient; we are watching things that happened more than 1,000 years ago,” the team wrote. “They’re almost certainly caused by something ordinary, at least on a cosmic scale. And yet that makes them more interesting, not less. But most of all, they’re mysterious. What the heck was going on there, all those centuries ago?”
In addition to providing the first truly solid explanation for Tabby’s Star, this study is also an indication of how the field of astronomical research is changing. Basically, it was conducted by experts in the field who conducted an observation campaign using state-of-the-art instruments. However, it would not have been possible without the engagement and financial support it received from the public.
The original discovery was also possible thanks in large part to citizen scientists and planet hunters, who helped sift through the massive amounts of data obtained by the Kepler mission. As Boyajian herself indicated, the assistance of the public is what made the biggest difference:
If it wasn’t for people with an unbiased look on our universe, this unusual star would have been overlooked. Again, without the public support for this dedicated observing run, we would not have this large amount of data… It’s exciting. I am so appreciative of all of the people who have contributed to this in the past year – the citizen scientists and professional astronomers. It’s quite humbling to have all of these people contributing in various ways to help figure it out.”
Of course, there is much work to be done and many more questions that need to be answered. But in the meantime, it seems that the single-greatest question about Tabby’s Star – a natural cause or possible evidence of alien activity? – has been tentatively resolved. For those who were hoping that it might be the long-awaited resolution to Fermi’s Paradox I think it’s fair to say we all knew this had to happen sooner or later.
And in the end, is it not better to know that strange and mysterious events have a natural explanation, rather than to not know one way or another? Sure, if you don’t know, it leaves you free to speculate and think what you want, but that’s hardly a scientific attitude. And if we ever want to find evidence of extra-terrestrial intelligence, we need to be able to distinguish natural phenomena from something unnatural.
Remember Carl Sagan’s famous words: “The absence of evidence is not the evidence of absence”? Well, that works both ways!
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