Back to Back Issues Page
Real World Physics Problems Newsletter - Tabby's Star, Issue #34
August 21, 2016

Tabby's Star

tabbys star

Source: NASA/JPL-Caltech/T. Pyle

The F-type main sequence star, known as Tabby's star (with official name KIC 8462852), is located about 1,500 light years from earth and is slightly larger than the Sun. Of the 150,000 stars observed by the Kepler space telescope over the last several years it has among the most unusual features of any known star. Its brightness is changing in a very unusual way; a way that is not easily explained by any known natural phenomenon. The Kepler space telescope is designed to detect light reduction in light emitted from stars due to the planets orbiting them. A planet, typically much smaller than a star, will block a small portion of its light when orbiting around it. If the path of the planet happens to lie between us (on earth) and the star we are able to detect the resulting reduction in starlight. This reduction in light is very small but is easily detected by the sensitive Kepler space telescope.

So what does this mean?

Normally not much, aside from just providing evidence that a planet, or planets, are orbiting a star, which is almost always true for every star out there. But in the case of Tabby's star, the frequency at which its light dims does not occur in a repeatable manner. You see, when planets orbit a star they do so at a constant rate - a consequence of the physics described by Newtonian mechanics. For example, the planets might orbit their parent star once every 30 days, which means that we would see the light from that star dim once every 30 days if we had a telescope pointed at it. This assumes of course that the orbit of the planet lies within the line of sight of an earth telescope pointed at the star. Most planets' orbits do not, but that's okay, and to be expected since the orientation of celestial bodies, and their motion, is quite random relative to us.

Some scientists have speculated that the unusual light pattern from Tabby's star could be evidence of an advanced alien civilization using the star's energy for their massive energy needs. The idea here is that the more advanced an alien civilization is, the greater its energy needs will likely be, up until it eventually ends up using a significant portion of the energy of its star, such as with an enormous array of solar panels surrounding the entire star (called a dyson sphere or dyson swarm). This could, in theory, explain the unusual pattern of reduction in light as emitted from the star, which follows a non-repeatable pattern, which could be indicative of something irregular and artificial orbiting the star, as observed by an external party such as us.

It turns out that the natural explanations brought forth so far to explain the irregular dimming of Tabby's star have not stood up to scrutiny; explanations such as a large swarm of comets orbiting the star, which could block the starlight in a non-repeatable way. Now, that doesn't mean that no natural explanations exist. It just means that none have been found so far. Most likely there is a natural explanation, but that won't stop people from wondering if it really could be aliens.

Scientists have determined that if aliens are using a significant portion of the star's energy, there will result a significant amount of waste heat which we could detect, which would lie in the mid-infrared portion of the electromagnetic spectrum. This is an inescapable consequence of the laws of thermodynamics. Energy cannot be destroyed, it can only change forms, and the common form of energy after being used is to end up as waste heat. Take a car for example; most of the energy of the fuel is lost as heat, and the remaining energy is used to move the car (i.e. perform useful work). However, to move the car, friction with the road and air must be overcome, along with internal friction of the engine and other moving parts in the car. Ultimately, this ends up as wasted heat as well. So essentially all the energy of the car's fuel ends up as waste heat. You can argue the same principle for energy received from a dyson sphere, or swarm. That energy could be used to "do something". And after that task, or tasks, are performed, and assuming none of the energy is stored anywhere, that energy will end up as waste heat in the mid-infrared. You can go much deeper than this to explain the precise reasons why, but it's a consequence of the laws of thermodynamics.

Unfortunately, scientists have not detected a larger than normal amount of infrared radiation from the vicinity of Tabby's star. This either means that there are no aliens using a big chunk of the star's energy, or the aliens are much more efficient than we could imagine at using the star's energy, in order to minimize the amount of waste heat produced so that other life forms (such as us) would not be able to detect them, or detect them as easily. There are good reasons for wanting to hide your existence from life forms elsewhere in the universe!

Scientists have also not detected any radio transmissions being sent from the vicinity of Tabby's star, which would be good evidence for the presence of aliens.

It's a fascinating topic for discussion. I will certainly be paying close attention to what ends up being discovered with regards to Tabby's star, because aliens or not, we're sure to learn a lot from it.

Till next time.


Back to Back Issues Page