The idea of one day traveling to another star system and seeing what is there has been the fevered dream of people long before the first rockets and astronauts were sent to space. But despite all the progress we have made since the beginning of the Space Age, interstellar travel remains just that – a fevered dream. While theoretical concepts have been proposed, the issues of cost, travel time and fuel remain highly problematic.
A lot of hopes currently hinge on the use of directed energy and lightsails to push tiny spacecrafts to relativistic speeds. But what if there was a way to make larger spacecraft fast enough to conduct interstellar voyages? According to Prof. David Kipping – the leader of Columbia University’s Cool Worlds lab – future spacecraft could rely on a Halo Drive, which uses the gravitational force of a black hole to reach incredible speeds.
During the 1960s, Freeman Dyson and Nikolai Kardashev captured the imaginations of people everywhere by making some radical proposals. Whereas Dyson proposed that intelligent species could eventually create megastructures to harness the energy of their stars, Kardashev offered a three-tiered classification system for intelligent species based on their ability to harness the energy of their planet, solar system and galaxy, respectively.
With missions that are now capable of locating extra-solar planets (i.e. the Kepler Space Observatory) scientists have been on the lookout for signs of possible alien megastructures. Unfortunately, aside from some very arguable results, no concrete evidence has yet come to light. Lucky for us, in a study from the Free University of Tbilisi, Professor Zaza Osmanov offers some new insight on why megastructures may have eluded us so far.
While fascinating, the idea of alien megastructures invariably suffers from the same problem as all other attempts to find signs of intelligent life in our Universe. Basically, if intelligent life exists, why have we consistently failed to find any evidence of it? This conundrum, which was summed up by Enrico Fermi in the 1950s (thereafter known as the Fermi Paradox), has hung like a shadow over all our efforts.
For example, in the summer of 2015, a team of astronomers announced that they found what might be an indication of an alien megastructure around Tabby’s Star (KIC 8462852). However, they were quick to point out that any number of possibilities could explain the strange dimming pattern coming from the star, and subsequent studies offered even more plausible explanations – such as the star having consumed a planet at some point in its past.
To this, Osmanov has argued that the problem is that we are looking in the wrong places. Last year, he wrote a research paper in which he ventured that an alien super civilization – i.e. one that was consistent with a Level II Kardashev civilization – would likely use ring-like megastructures to harness the power of their stars. This is in contrast to the traditional concept of a “Dyson’s Sphere”, which would consist of a spherical shell.
Furthermore, he argued that these Dyson Rings would likely be built around pulsars rather than stars, and offered estimates on their dimensions which were dependent on the rotational speed of the pulsar. According to Osmanov’s latest study, titled “Are the Dyson rings around pulsars detectable?“, Osmanov extends the problem of spotting alien megastructures to the observational realm.
Specifically, he addressed how alien megastructures could be spotted by identifying their infrared energy signatures, and at what kinds of distances. By examining how such structures would vary in terms of the amount of IR radiation they would emit, he believes that they could be spotted within our local Universe using existing instruments.
Once again, it comes down to the diameter of the structures, which would in turn depend on the type of pulsar they orbit. As he states in the paper:
“A couple of years earlier before publishing the paper of Kardashev, the prominent physicist Freeman Dyson has suggested that if such superadvanced (in the terminology of Kardashev, Level-II) extraterrestrials exist, for increasing efficiency of energy consumption they can construct a thin spherical shell with radius ?1AU surrounding a host star (Dyson 1960).It has been argued that for such distances the sphere will be in the so-called habitable zone (HZ) and therefore the sphere will have the temperature of the order of (200 – 300 K), making this object visible in the infrared spectrum.”
Extending this to pulsars, Osmanov estimates that the habitable zone around a relatively slowly-rotating pulsar (with a period of about half a second) would be on the order of 0.1 AU. According to his calculations, a ring-like megastructure that orbited a pulsar at this distance would emit temperatures on the order of 390 K (116.85 °C; 242.33 °F), which means that the megastructure would be visible in the IR band.
From this, Osmanov concludes that modern IR telescopes – such as the Very Large Telescope Interferometer (VLTI) and the Wide-field Infrared Survey Explorer (WISE) – would have the necessary capacity to monitor nearby pulsars for signs of alien megastructures. He further concludes that for this purpose, these telescopes would have an effective range of up to 200 parsecs (~652 light years).
In addition, he goes on to state that within this volume of space, multiple candidates could be found and examined using these same existing instruments:
“We have considered the sensitivity of VLTI and by taking into account its higher possible angular resolution, 0.001 mas, it has been shown that the maximum distance ~0.2 kpc leads to the IR spectral density of the order of 7.4 mJy, which in turn, can be detected by the VLTI. We have argued that by monitoring the nearby zone of the Solar System approximately 64 pulsars are expected to be located inside it.”
Beyond these distances, up to the kiloparsec range (about 3260 light years), the angular resolution of these telescopes would not be enough to detect the structure of any rings. As such, finding megastructures at this distance would require telescopes that can conduct surveys in the UV band – which corresponds to the surface temperatures of neutron stars (7000 K). However, this would have to wait upon the development of more sensitive instruments.
“As we see, the search of infrared rings is quite promising for distances up to -0.2 kpc, where one will be able to monitor potentially 64 ± 21 pulsars by using the IR instruments,” he concluded. “Observation of distant pulsars (up to -1kpc), although will significantly increase the total number of potential objects – to 1600 ± 530, but at this moment the UV instruments cannot provide such a level of sensitivity.”
So while the range would be limited, the opportunities for testing this hypothesis would not. All told, between 43 and 85 candidates exist within the observable volume of space, according to Osmanov’s estimates. And with existing IR telescopes – and next-generation telescopes like the James Webb Space Telescopes – up to the task, some surveys could be conducted that would yield valuable information either way.
The concept of alien megastructures remains a controversial one, and for good reason. For one, the potential evidence for such structures – i.e. the periodic dimming of a star – can easily be explained by other means. Second, there is an undeniable degree of wishful thinking when it comes to the search for extra-terrestrial intelligence, which means that any findings could be subject to bias.
Nevertheless, the search for intelligent life remains a very fascinating field of study, and a necessary one at that. Not only would finding other examples of life in our Universe put to rest one of the most burning existential questions of all time – are we alone? – it would also allow us to learn a great deal about what other forms life could take. Is all life carbon based, are there other possibilities, etc? We would like to know!
In the end, the Fermi Paradox will only be resolved when we find definitive evidence that there is intelligent life out there other than our own. In the meantime, we can expect that we will keep searching until we find something. And anything that make this easier by telling us where we should (and what specifically to look for) is sure to help.
Beam us up, Scotty. There’s no signs of intelligent life out there. At least, no obvious signs, according to a recent survey performed by researchers at Penn State University. After reviewing data taken by the NASA Wide-field Infrared Survey Explorer (WISE) space telescope of over 100,000 galaxies, there appears to be little evidence that advanced, spacefaring civilizations exist in any of them.
First deployed in 2009, the WISE mission has been able to identify thousands of asteroids in our solar system and previously undiscovered star clusters in our galaxy. However, Jason T. Wright, an assistant professor of astronomy and astrophysics at the Center for Exoplanets and Habitable Worlds at Penn State University, conceived of and initiated a new field of research – using the infrared data to assist in the search for signs of extra-terrestrial civilizations.
And while their first look did not yield much in the way of results, it is an exciting new area of research and provides some very useful information on one of the greatest questions ever asked: are we alone in the universe?
“The idea behind our research is that, if an entire galaxy had been colonized by an advanced spacefaring civilization, the energy produced by that civilization’s technologies would be detectable in mid-infrared wavelengths,” said Wright, “exactly the radiation that the WISE satellite was designed to detect for other astronomical purposes.”
This logic is in keeping with the theories of Russian astronomer Nikolai Kardashev and theoretical physicist Freeman Dyson. In 1964, Kardashev proposed that a civilization’s level of technological advancement could be measured based on the amount of energy that civilization is able to utilize.
To characterize the level of extra-terrestrial development, Kardashev developed a three category system – Type I, II, and III civilizations – known as the “Kardashev Scale”. A Type I civilization uses all available resources on its home planet, while a Type II is able to harness all the energy of its star. Type III civilizations are those that are advanced enough to harness the energy of their entire galaxy.
Similarly, Dyson proposed in 1960 that advanced alien civilizations beyond Earth could be detected by the telltale evidence of their mid-infrared emissions. Believing that a sufficiently advanced civilization would be able to enclose their parent star, he believed it would be possible to search for extraterrestrials by looking for large objects radiating in the infrared range of the electromagnetic spectrum.
These thoughts were expressed in a short paper submitted to the journal Science, entitled “Search for Artificial Stellar Sources of Infrared Radiation“. In it, Dyson proposed that an advanced species would use artificial structures – now referred to as “Dyson Spheres” (though he used the term “shell” in his paper) – to intercept electromagnetic radiation with wavelengths from visible light downwards and radiating waste heat outwards as infrared radiation.
“Whether an advanced spacefaring civilization uses the large amounts of energy from its galaxy’s stars to power computers, space flight, communication, or something we can’t yet imagine, fundamental thermodynamics tells us that this energy must be radiated away as heat in the mid-infrared wavelengths,” said Wright. “This same basic physics causes your computer to radiate heat while it is turned on.”
However, it was not until space-based telescopes like WISE were deployed that it became possible to make sensitive measurements of this radiation. WISE is one of three infrared missions currently in space, the other two being NASA’s Spitzer Space Telescope and the Herschel Space Observatory – a European Space Agency mission with important NASA participation.
WISE is different from these missions in that it surveys the entire sky and is designed to cast a net wide enough to catch all sorts of previously unseen cosmic interests. And there are few things more interesting than the prospect of advanced alien civilizations!
To search for them, Roger Griffith – a postbaccalaureate researcher at Penn State and the lead author of the paper – and colleagues scoured the entries in the WISE satellites database looking for evidence of a galaxy that was emitting too much mid-infrared radiation. He and his team then individually examined and categorized 100,000 of the most promising galaxy images.
And while they didn’t find any obvious signs of a Type II civilization or Dyson Spheres in any of them, they did find around 50 candidates that showed unusually high levels of mid-infrared radiation. The next step will be to confirm whether or not these signs are due to natural astronomical processes, or could be an indication of a highly advanced civilization tapping their parent star for energy.
In any case, the team’s findings were quite interesting and broke new ground in what is sure to be an ongoing area of research. The only previous study, according to the G-HAT team, surveyed only about 100 galaxies, and was unable to examine them in the infrared to see how much heat they emitted. What’s more, the research may help shed some light on the burning questions about the very existence of intelligent, extra-terrestrial life in our universe.
“Our results mean that, out of the 100,000 galaxies that WISE could see in sufficient detail, none of them is widely populated by an alien civilization using most of the starlight in its galaxy for its own purposes,” said Wright. “That’s interesting because these galaxies are billions of years old, which should have been plenty of time for them to have been filled with alien civilizations, if they exist. Either they don’t exist, or they don’t yet use enough energy for us to recognize them.”
Alas, it seems we are no closer to resolving the Fermi Paradox. But for the first time, it seems that investigations into the matter are moving beyond theoretical arguments. And given time, and further refinements in our detection methods, who knows what we might find lurking out there? The universe is very, very big place, after all.
The research team’s first research paper about their Glimpsing Heat from Alien Technologies Survey (G-HAT) survey appeared in the Astrophysical Journal Supplement Series on April 15, 2015.