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.Continue reading “Finding Alien Megastructures Around Nearby Pulsars”
Do Stars Move? Tracking Their Movements Across the Sky
The night sky, is the night sky, is the night sky. The constellations you learned as a child are the same constellations that you see today. Ancient people recognized these same constellations. Oh sure, they might not have had the same name for it, but essentially, we see what they saw.
But when you see animations of galaxies, especially as they come together and collide, you see the stars buzzing around like angry bees. We know that the stars can have motions, and yet, we don’t see them moving?
How fast are they moving, and will we ever be able to tell?
Stars, of course, do move. It’s just that the distances are so great that it’s very difficult to tell. But astronomers have been studying their position for thousands of years. Tracking the position and movements of the stars is known as astrometry.
We trace the history of astrometry back to 190 BC, when the ancient Greek astronomer Hipparchus first created a catalog of the 850 brightest stars in the sky and their position. His student Ptolemy followed up with his own observations of the night sky, creating his important document: the Almagest.
In the Almagest, Ptolemy laid out his theory for an Earth-centric Universe, with the Moon, Sun, planets and stars in concentric crystal spheres that rotated around the planet. He was wrong about the Universe, of course, but his charts and tables were incredibly accurate, measuring the brightness and location of more than 1,000 stars.
A thousand years later, the Arabic astronomer Abd al-Rahman al-Sufi completed an even more detailed measurement of the sky using an astrolabe.
One of the most famous astronomers in history was the Danish Tycho Brahe. He was renowned for his ability to measure the position of stars, and built incredibly precise instruments for the time to do the job. He measured the positions of stars to within 15 to 35 arcseconds of accuracy. Just for comparison, a human hair, held 10 meters away is an arcsecond wide.
Also, I’m required to inform you that Brahe had a fake nose. He lost his in a duel, but had a brass replacement made.
In 1807, Friedrich Bessel was the first astronomer to measure the distance to a nearby star 61 Cygni. He used the technique of parallax, by measuring the angle to the star when the Earth was on one side of the Sun, and then measuring it again 6 months later when the Earth was on the other side.
Over the course of this period, this relatively closer star moves slightly back and forth against the more distant background of the galaxy.
And over the next two centuries, other astronomers further refined this technique, getting better and better at figuring out the distance and motions of stars.
But to really track the positions and motions of stars, we needed to go to space. In 1989, the European Space Agency launched their Hipparcos mission, named after the Greek astronomer we talked about earlier. Its job was to measure the position and motion of the nearby stars in the Milky Way. Over the course of its mission, Hipparcos accurately measured 118,000 stars, and provided rough calculations for another 2 million stars.
That was useful, and astronomers have relied on it ever since, but something better has arrived, and its name is Gaia.
Launched in December 2013, the European Space Agency’s Gaia in is in the process of mapping out a billion stars in the Milky Way. That’s billion, with a B, and accounts for about 1% of the stars in the galaxy. The spacecraft will track the motion of 150 million stars, telling us where everything is going over time. It will be a mind bending accomplishment. Hipparchus would be proud.
With the most precise measurements, taken year after year, the motions of the stars can indeed be calculated. Although they’re not enough to see with the unaided eye, over thousands and tens of thousands of years, the positions of the stars change dramatically in the sky.
The familiar stars in the Big Dipper, for example, look how they do today. But if you go forward or backward in time, the positions of the stars look very different, and eventually completely unrecognizable.
When a star is moving sideways across the sky, astronomers call this “proper motion”. The speed a star moves is typically about 0.1 arc second per year. This is almost imperceptible, but over the course of 2000 years, for example, a typical star would have moved across the sky by about half a degree, or the width of the Moon in the sky.
The star with the fastest proper motion that we know of is Barnard’s star, zipping through the sky at 10.25 arcseconds a year. In that same 2000 year period, it would have moved 5.5 degrees, or about 11 times the width of your hand. Very fast.
When a star is moving toward or away from us, astronomers call that radial velocity. They measure this by calculating the doppler shift. The light from stars moving towards us is shifted towards the blue side of the spectrum, while stars moving away from us are red-shifted.
Between the proper motion and redshift, you can get a precise calculation for the exact path a star is moving in the sky.
We know, for example, that the dwarf star Hipparcos 85605 is moving rapidly towards us. It’s 16 light-years away right now, but in the next few hundred thousand years, it’s going to get as close as .13 light-years away, or about 8,200 times the distance from the Earth to the Sun. This won’t cause us any direct effect, but the gravitational interaction from the star could kick a bunch of comets out of the Oort cloud and send them down towards the inner Solar System.
The motions of the stars is fairly gentle, jostling through gravitational interactions as they orbit around the center of the Milky Way. But there are other, more catastrophic events that can make stars move much more quickly through space.
When a binary pair of stars gets too close to the supermassive black hole at the center of the Milky Way, one can be consumed by the black hole. The other now has the velocity, without the added mass of its companion. This gives it a high-velocity kick. About once every 100,000 years, a star is kicked right out of the Milky Way from the galactic center.
Another situation can happen where a smaller star is orbiting around a supermassive companion. Over time, the massive star bloats up as supergiant and then detonates as a supernova. Like a stone released from a sling, the smaller star is no longer held in place by gravity, and it hurtles out into space at incredible speeds.
Astronomers have detected these hypervelocity stars moving at 1.1 million kilometers per hour relative to the center of the Milky Way.
All of the methods of stellar motion that I talked about so far are natural. But can you imagine a future civilization that becomes so powerful it could move the stars themselves?
In 1987, the Russian astrophysicist Leonid Shkadov presented a technique that could move a star over vast lengths of time. By building a huge mirror and positioning it on one side of a star, the star itself could act like a thruster.
Photons from the star would reflect off the mirror, imparting momentum like a solar sail. The mirror itself would be massive enough that its gravity would attract the star, but the light pressure from the star would keep it from falling in. This would create a slow but steady pressure on the other side of the star, accelerating it in whatever direction the civilization wanted.
Over the course of a few billion years, a star could be relocated pretty much anywhere a civilization wanted within its host galaxy.
This would be a true Type III Civilization. A vast empire with such power and capability that they can rearrange the stars in their entire galaxy into a configuration that they find more useful. Maybe they arrange all the stars into a vast sphere, or some kind of geometric object, to minimize transit and communication times. Or maybe it makes more sense to push them all into a clean flat disk.
Amazingly, astronomers have actually gone looking for galaxies like this. In theory, a galaxy under control by a Type III Civilization should be obvious by the wavelength of light they give off. But so far, none have turned up. It’s all normal, natural galaxies as far as we can see in all directions.
For our short lifetimes, it appears as if the sky is frozen. The stars remain in their exact positions forever, but if you could speed up time, you’d see that everything is in motion, all the time, with stars moving back and forth, like airplanes across the sky. You just need to be patient to see it.
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When Will Humanity Become a Type III Civilization?
Now, I’m no futurist, but I think I can predict one thing. Humans love to use energy, and in the future, we’re going to use even more of the stuff.
Let’s hope it’s clean energy, like that handy source of photons in the sky: the Sun. Not dirty forms of energy, like screams, unobtainium, liquid Shwartz, or using humans as batteries.
Once we really get our hands on a clean, unlimited source of energy, you can expect our usage to grow and grow until every human on Earth is using as much energy as a small country.Continue reading “When Will Humanity Become a Type III Civilization?”
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100,000 Galaxies, and No Obvious Signs of Life
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.
Further Reading: Astrophysical Journal via EurekAlert, JPL-NASA