Looney Tunes character Marvin
We really are obsessed with finding life in space. If it’s not Martian invaders á la Orson Welles it’s Marvin the Martian hunting down poor old Bugs Bunny. Tales of visitations from and abductions by aliens abound on the internet. And we have telescopes dedicated to listening for signals or spotting unusual variations in the light from Sun like stars.
There have been two in particular that have fuelled the imagination, especially of copywriters. The first is KIC 8462852 also known as Tabby’s star after one its discoverer Tabetha Boyajian. This star is 1,480 light-years away in Cygnus and is an f-type star, slightly younger than the Sun but otherwise pretty similar. In October 2015 Astronomers at Yale found it displayed some unusual light variations.
The position of Tabby’s star.
A lot of stars vary in brightness and output (even the Sun albeit very little) and are well understood; they may have companion stars crossing in front of them blocking off some light, think Algol (beta Persei) or there may be a dense cloud that passes by doing the same thing as it orbits a star (as is the case with epsilon Aurigae, which has a noticeable 27 year period.)
(Notice how much more regular are the dips for Algol in brightness than for Tabby’s star below.)
The way the light changes for these types of objects is pretty straightforward and smooth. Not so for Tabby’s star; astronomers noticed that it faded at first by about 0.34% over a few years but it then in just 200 days it faded by 2.5%. It then carried on fading in its previous way. No star near-by showed similar patterns.
The Kepler space telescope had been monitoring Tabby’s star for a number of years and showed that in 2011 and 2013 the star dimmed a very dramatic way. It had faded by a whopping 22%. This dimming could last between five and eighty days at a time. Something very big had to be passing in front of it. (Flux refers here to the brightness of the object.)
This led some to suggest a Dyson Sphere. In 1960 theoretical physicist Freeman Dyson suggested that an advanced civilisation might be able to build and sphere or shell to encase a star to harness its power, or that a swarm of satellites or solar panels could surround a star, known as a Dyson swarm, could do the same thing. A Dyson swarm would be easier than an all encompassing sphere to build but still is beyond our ability. Other fanciful suggestions have been gigantic space habitation platforms or even artificially built occulting masks that deliberately dim the star to alert other species that there is life there.
As a result a lot of radio telescopes were turned towards the star to listen for any signal that might suggest life. Sadly nothing has, so far, been heard.
As with the ‘Little Green Men’ signal that ushered in the discovery of the super regular emissions of pulsars people are quick to imagine the fanciful; the reality is likely to be slightly more prosaic but none the less interesting. Current theories suggest the unusual diming may be caused by the break-up of a lot of really large comets orbiting the star (although how this would happen is debatable) or it could even be errors with the data…we still don’t yet know.
But, if you’re hoping for aliens another 234 stars have piqued interest. A paper released on arXiv.org claims that after looking at 2.5 million stars surveyed by the Sloan Digital Sky Survey 234 have a very unusual and puzzling light signature. One of the lead astronomers for this paper EF Borra (who works in Canada) claims these light patterns are similar to those he proposed in an earlier paper that might come from an alien civilisation signalling their existence to others. (Here is the link to the paper; https://arxiv.org/abs/1610.03031 )
Could they be from aliens? This is what the scientists themselves say in their pre-amble to the article; “We find that the detected signals have exactly the shape of an ETI signal predicted in the previous publication and are therefore in agreement with this hypothesis. The fact that they are only found in a very small fraction of stars within a narrow spectral range centred near the spectral type of the sun is also in agreement with the ETI hypothesis. However, at this stage, this hypothesis needs to be confirmed with further work.” They do go on to add a note of caution; “Although unlikely, there is also a possibility that the signals are due to highly peculiar chemical compositions in a small fraction of galactic halo stars.”
(ETI stands for Extra-Terrestrial Intelligence.)
Well a lot more studying of these signals from a lot more institutes with a lot more equipment will be needed before any definite answer can be given. Perhaps the brand new Chinese radio telescope FAST may look at these signals…
FAST stands for Five hundred metre Aperture Spherical Telescope and is one of the largest radio telescopes in the world. In area it is roughly the equivalent to thirty football pitches or 200,000 square meters. Work began on building it in 2011 and it is already built and after undergoing tests before beginning its working life on the 25th September 2016. The web page for FAST is; http://fast.bao.ac.cn/en/
There is a larger radio telescope in Russia called RATAN 600 which is 576m in diameter, but, unlike FAST, is composed of segments that make up the whole dish (895 of them of size 2×7.4 m.) It was involved in the detection of an unusual and regular signal which could have been alien in origin, however after other observatories failed to repeat the observation, and because of the frequency it was observed it was decided that RATAN had picked up signals from a secret military reconnaissance satellite.
RATAN commemorated in a 1987 stamp.
So, you do need to be careful when making assumptions about unusual observations, as it could be alien in origin or more likely something else all together!