Astronomy is the oldest of the natural sciences. When
mankind decided that lifting their eyes up to the hills wasn’t enough, and
aimed higher for truth, there they were – the stars. Our quest for knowledge
about that which we could see, and that which we could not, has driven human
civilizations to heights not dreamed of. But, as JBS Haldane noted, the
universe is not only stranger than we imagine, it is stranger than we can
imagine. We are still just scratching at the surface of what’s out there.
In 2009, the Kepler space
observatory was launched, and one of the stars it observed was KIC 8462852,
approximately 1480 light years from us. It’s a rather unwieldy name, but now,
after a paper published on 17 October, it is colloquially known as Tabby’s star
(after Tabetha S Boyajian) or the WTF star (Where’s the flux – Boyajian’s paper
about the star.) Boyajian is part of the Planet Hunters project, a group of
people analysing the fluctuation in the brightness of stars to detect
extrasolar planets.
Tabby’s star was different though. A planet the size of
Jupiter would obscure the brightness of a star by about 1%, but on 5 March
2011, Tabby’s star had its luminosity drop by 15%, and by 22% on 28 February
2013. This was unprecedented, and some of the theories surrounding what caused
it requires some background.
In 1964, Nikolai Kardashev, a Soviet astronomer, proposed a
method of measuring a civilization’s level of technological advancement based
on the energy it is able to tap into. He proposed three categories – Type I,
where a civilization uses all resources available on its home planet, Type II,
where it harnesses the energy of its star, and Type III, where an entire galaxy
is utilized.
The American astronomer Carl Sagan expanded on his idea,
suggesting intermediate values based on a logarithmic scale between these types
based on the expected power outputs for the civilizations mentioned above. Type
I would harness approximate 10^16 watts (10 to the power 16, or a 1 followed by
16 zeros), with Type II consuming 10^26 watts, and Type III 10^36 watts. Based
on the total world energy consumption in 2012 (17.54 terawatts, or 17.54 x
10^12 watts) human civilization is currently a Type 0.724 civilization on the
Kardashev scale. It is estimated that humanity will reach Type I in about 100
to 200 years.
Yet it was a few years earlier than Kardashev that Freeman J
Dyson postulated about the hypothetical megastructure that would make a Type II
civilization possible. In his 1960 paper, “Search for Artificial Stellar
Sources of Infrared Radiation,” Dyson speculated about the increased energy
needs of civilizations as they grow, and proposed a system of orbiting
structures designed to collect all energy produced by a star, and how such a
structure could be identified by its unusual emissions spectrum compared to the
star.
His concept was popularized as a Dyson Sphere - a shell
around the sun. Such a sphere would intercept the full 3.84 x 10^26 watts of
solar power output (about 21 trillion times humanity’s current power output) with
a surface area about 550 million times the surface of the earth.
Such a construct is beyond our current capabilities, but Dyson’s
original concept was actually what is known as a Dyson swarm – a large number
of independent satellites orbiting in a dense formation around a star. A large
cloud of such emitters could alter the light emitted by a star, and disrupt its
luminance when observed from outside. And thus we are back to Tabby’s star,
which experiences a significant drop in luminosity every 750 days.
Boyajian’s paper examined several hypothesis for this
strange dimming, from instrument defects to an asteroid belt pileup and even
impacts of a planetary scale. The most likely natural cause, she theorized, would
be a close pass of another star that pulled a sea of comets into orbit around
the star. Enough of them could cause this kind of dimming. But Boyajian only
considered natural sources in her paper.
The SETI Institute has naturally taken an interest. The
Search for Extra Terrestrial Intelligence has long been analysing the sky
searching for radio waves indicating potential life elsewhere, and this has
been one of the very few times they’re been approached by astronomers with data
that is very atypical. On 19 October 2015 they had begun using the Allen Telescope
Array to search for radio waves at frequencies associated with technological
activity, with potential follow ups if something interesting is detected.
Still, SETI’s philosophy is that the alien hypothesis is the last resort.
Latest theories indicate that this phenomenon could merely
be an artefact of the star having an oblate disc, resulting in gravity darkened
regions and creating the non-uniform dips in flux, but so far, none of the
theories have been verified. It remains
human nature to speculate, and, after all, if these are megastructures, they
would have been built already in the 6th century CE. Only time will
reveal what has happened since.
The stars started us on our quest for knowledge. It seems
they still have a few things to teach us yet.
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