Boyajian’s Star (aka Tabby’s Star) – Contextualizing the findings so far
Since time immemorial the human race has always been fascinated by stars and space. We have looked at them and made segregated them into shapes of the zodiac, amongst other things. But our desire to know more about them has never been satiated. Our eternal question – are we alone or are there others – both equally scary as per Fermi – has not been answered nor do we see any answers to that on the horizon.
It can be argued that we’ve been late entrants if looked at from the view of the Universe. According to science, the Big Bang happened close to 14 billion years ago and our own Sun got formed about 4.6 billion years ago. Life started on Earth about 4 billion years ago; humans – Homo sapiens – about 100,000 years ago. And we started with modern technology a mere 100 years ago.
According to Panspermia Theory, life “could have” started when the Big Bang was just 10-20 million years old. If we were to even assume that life originated on a remote planet maybe twice earlier than on Earth, which puts a civilization at current point in time with such an advanced technology we cannot even fathom.
In 1964, a Soviet astronomer Nikolai Kardashev proposed a hypothesis to determine advancement of a civilization based on their energy consumption.
- Type 0 – Currently we are a Type 0 civilization. We are dependent on dead plants and animals to sustain our civilization.
- Type I – A species that is able to harness all the energy available to it from a neighboring star. In effect, it means harnessing all the solar power that falls on the Earth and also harness energy generated by earthquakes etc.
- Type II – A species that can harness the power of their entire star. Most popular hypothesis is building of a Dyson Sphere which would then absorb all the energy from a star like Sun.
- Type III – A civilization that can harness and consume the entire energy produced in its own galaxy.
Though Kardashev thought Type IV and above was too advanced, this scale has been extended to Type IV and beyond. Professor Michio Kaku suggests that humans may attain Type I status in 100-200 years, Type II in a few thousand years and Type III in 100,000 to a million years . So for a Type I or Type II civilization to cater to its enormous energy needs a Dyson Sphere could be a way out.
In 1960, Freeman Dyson speculated that a megastructure of some sort that completely encompasses a star to capture all or most of its power output could possibly be built. In his paper “Search for Artificial Stellar Sources of Infra-Red Radiation ”, he proposed a system of orbiting structures designed to intercept and collect all the energy produced by a Sun . If such a structure were to be built around a star, then, to an observer far off from that system, there could potentially be some “dips” in the emission spectrum when compared to a normal star.
For example, if we were to observe a set of far off stars then we would have a track for their emissions over period of time. A star which was blocked even a little bit would have these “dips”. The block could be a planet or asteroid belt or something else entirely. But the key hypothesis of Dyson is that if we could observe the dips in emissions from a star especially when compared to other nearby stars, and for which we do not have any organic reason, it could indicate an advanced alien civilization.
If one were to observe our Solar System from outside of it, then one would see dips in the Sun’s emissions every year when planets like Earth, Venus, and Jupiter etc. pass in between the observer and the Sun. A planet the size of Jupiter the dip would be about 1%. Whereas when a planet size of Earth passes the dip would be considerably less given the Earth is 318 time smaller than Jupiter.
The Kepler spacecraft was launched in 2009 with one mission objective to find other Earth size planets in the habitable zones orbiting stars. The spacecraft has just one instrument and it is ultra-sensitive to light. It captures the brightness of distant stars and transmits the data to mission control. The Kepler’s light sensors detect the drop in a star’s brightness whenever a plant passes in front of that star. When such periodic and predictable dips are observed, a new planet is confirmed outside our solar system.
The KIC, or Kepler Input Catalog, is the primary source of information about objects observed as part of the ground-based Kepler Spectral Classification Program (SCP) . The catalog includes "mass, radius, effective temperature, log (g), metallicity, and reddening extinction". It is a publicly searchable database and is widely used by Planet Hunters [7}.
Kepler has data on about 150,000 stars and it is not possible for scientists to look at the data generated for all of these. A group of citizen scientists – Planet Hunters – try to look at the enormous data from Kelper to find and report any dips that they observe in the stars. While at it, they spotted a huge anomaly in the data. They detected transits of something(s) in front of this star which last for a few days and are irregularly shaped, aperiodic, and massive which rules out planets. A team lead by Astronomer Tabetha Boyajian wrote a paper where they tried to generate some plausible scenarios for this behavior but call for more observation of this star to formulate a workable theory. Since then the star’s been called as Tabby’s Star or Boyajian’s Star or WTF Star [on the title of the paper Boyajian submitted “Where’s The Flux? ”].
The dips in the emissions as observed by Tabby et al over a period of four years is shown here:
As can be seen from the image above, two of these dips (numbered 5 and 8) are around 20%, which is only achievable by an object that is more about star sized than planet sized. Dips 9 and 10 are also considerably larger than any planetary transit . Another important thing to note is that the events took place on a time scale of days, and some of them about 10 days. This is a big part of the puzzle.
This paper generated a lot of interest in the star and subsequently another scientist Bradley Schaefer looked at a 100-year long series of photographic plates from a collection at Harvard and concluded the star has actually been dimming for 100 years . For his study, Schaefer choose 12 stars as control stars apart from this particular start. He found out that between 1890 and 1989 there were periods where the star had dims of 20%!!
Schaefer further notes “Ockham’s razor tells us that it is very unlikely that one star will suffer two different mechanisms that are unique to that star and that both are only manifest in dimming the starlight by up to 20%.” This was the second independent confirmation that there is something going on with the star.
Additionally, astronomers Ben Montet and Joshua Simon looked for the long term dimming in Kepler's dataset as it should be detectable if Schaefers’ is correct. What they found was something astonishing: Not only did the star’s light output occasionally dip by up to 20 percent, its total stellar flux diminished continuously by about 3% over the course of four years. The astronomers looked at 500 other stars in the vicinity, and saw nothing else like it . This is independent of the shorter term large dips (as much as 20%) that the Boyajian’s team investigated.
Now for some basic physics. If some solid (or liquid) object absorbs 20% of the energy of the light from a source, it should heat up, and then basic physics says that energy will be emitted in infrared light. So, if one were to plot the energy we're seeing vs. wavelength of light, then we should see the normal light from Boyajian’s star, and then a bump out in the infrared. The "bump" is what is called an "infrared excess", and Boyajian’s team looked for one in the space telescope data available to them, and with a ground based telescope. They did not see any excess .
Boyajian’s team examined all the more obvious explanations:
- the star itself exhibits variability
- big clumps of dust orbiting the star
- catastrophic collisions
- planets in the process of formation, possibly with very large ring systems
- a swarm of large comets
All of these are ruled out by the data, except for the last one. They couldn’t rule out only the last one with the data that we currently have.
Enter Jason Wright an astronomer at Penn State who heads the Glimpsing Heat from Alien Technologies (GHAT) program. Based on the information that Tabby had provided along with all the analysis and data available, Professor Wright opined that Boyajian’s star’s an excellent case for SETI (Search for Extra Territorial Intelligence) . In his blog at AstroWright, Professor Wright has been methodically going over both natural and not-so-natural causes for the dips in this star . He opined that one possible explanation for this phenomenon could be an alien megastructure.
But the perplexing thing is the lack of excess infrared radiation. Prof. Wright writes that “Conservation of energy means that when one is done using energy for some purpose, one must expel it or else store it (though in the long run you can’t keep storing more and more energy). One might object that an arbitrarily advanced alien civilization could overcome this limitation, and it’s true that if alien civilizations inevitably violate conservation of energy, then our search will fail. But conservation of mass-energy is a fundamental a physical law we have, so it is reasonable from a physics perspective to search for the energy in waste heat, which should exist if alien civilizations do. ”
One very interesting thing to note is that the Boyajian’s Star is about 1500 light years away from us. It means that the current data that we are observing is that which has left the star 1500 years ago. To put that in perspective, if the people on that star were to observe India, Gupta dynasty would be ruling over India and Aryabhatta would have been alive!!
So what’s next?
At present, we do not have enough data to propose any reason that can withstand scrutiny. All we have is a bunch of hypothesis. The James Webb Space Telescope is still about 3 years away from on-orbit commissioning, and probably about 4 years from generating any meaningful data about this star. However, skilled amateur astronomers are out in clear nights, keeping a watch on Tabby's star for anomalous dimming events.
Prof Wright mentions that -one way out of the lack of excessive Infrared could be that the alien civilization is doing something with the radiation, that is, it's allowed, with the laws of thermodynamics, to use some fraction of the energy in a low-entropy way and only dump the last bits out of high entropy. It could radiate it away at low entropy as communication. They could use it as Kardashev originally proposed, as radio. So if that's right, then maybe there's something to decode in radio waves .
So that is what is up next. On September 14, 2016 – GAIA Parallax data was released. Initial estimate was 391 parsecs with an error of 0.307 which would place the distance of Boyajian’s Star somewhere between 1139 to 1450 light years away. Prof Wright had earlier opined that if the distance is within 400 parsecs then it would be hard to explain the dimming with Interstellar Medium [i.e. dust, asteroids, comets etc.] And that if the distance were to be less than 400 parsecs then it would give credence to non-ISM non-dust explanation Spherical swarm of megastructures, Polar Spots and, Pulsations. The data released by GAIA is not conclusive enough to make a call on one of these possible explanations.
Then in October, Prof Wright, Prof Boyajian et al are going to point the world's largest fully steerable radio telescope – the Green Bank Telescope towards the Boyajian’s star hoping to find any radio waves. This could give us a much better idea of what it is that is blocking Boyajian’s Star. Whether this will solve or deepen the mystery, no one knows.
Note: This is my attempt to give some background to the enormous chatter around “Tabby’s Star” [now being called Boyajian’s Star]. I say “some” since each of the subheadings have been subject of many, many Doctoral dissertations. Blame for any misrepresentation of facts lies entirely with me.
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