13 billion years ago, the Milky Way was formed. Near the beginning of the Universe, some of our galaxy's oldest stars were created. We know of at least one technological civilization that has been created in all these eons.We know that the galaxy is ancient and can produce life. So why aren't we hearing from anyone else?If another civilization were only 0.1 percent older than ours, they would be millions more advanced than us and likely have a longer lifespan. Shouldn't the Milky Way already be full of alien colonies and ships, if we are on the brink of sending life to other planets?Perhaps. It's possible, however, that we have been searching in the wrong places. Recent computer simulations by Jason T. Wright and others. Recent computer simulations by Jason T. Wright et al. suggest that the core of the galaxy might be the best place to search for ancient spacefaring civilizations. This is a target relatively unknown in the hunt for extra terrestrial intelligence.Above: Animation depicting the settlement of the galaxy. Magenta spheres and unsettled star magenta points represent settled stars. White cubes signify a settlement ship in transit. Galactic shear is responsible for the formation of the spiral structure. The rate of colonization increases dramatically once the Galaxy's center has been reached. (Credit to Wright et. al.The ChurnAn older mathematical model of space colonization attempted to predict the time it would take for a civilization spread across the Milky Way. Due to the large size of the Milky Way galactic colonization may take longer than the galaxy's age.This simulation's accounting for the motions of the stars in the galaxy is a distinctive feature. The Milky Way isn't static as previously assumed. It is a churning, swirling mass. In motion, stars would allow colonization probes or vessels to fly among them. New simulations reveal that stellar motion helps in colonization and contributes to the spreading of civilizations.This simulation is based upon previous research by Jonathan Carroll Nellenback et. al. The simulation was based on previous research by Jonathan Carroll-Nellenback et al., which suggested that a hypothetical civilization could spread at sublight speeds through a moving galaxie. This simulation assumes that a civilization uses ships traveling at speeds comparable to our spacecraft (30 km/s).A ship that arrives on a virtual world can be considered a colony. It can launch another craft every 100,000 year if it is within range.The range of simulated spacecraft is 10 light-years with a maximum travel time of 300,000. Technology from a virtual colony was designed to last 100,000,000 years before it dies. However, there is the possibility to be resettled in case another colony moves into range via galactic motion.These are the dramatic results. The galaxy's rotation creates a wave, or "front", of colonization. The galactic core's density accelerates colonization once the front reaches it. Even with the most conservative speed limits, the majority of the galaxy could still be colonized in less that a billion years. This is a fraction of its total age.Line of sightThe simulation's results confirm past proposals of Vishal Gajjar and co. To search the galactic centre for signs of life. The galaxy's center can be colonized quickly and also scanned efficiently for technology.The galaxy's center is within our direct sight. It covers the area of space that is the most dense relative to us. The galaxy was formed from the inside out. This means that the center is filled by older planets, which gives life more time to develop.The center can also be used to "talk" with a central point in the galaxy. To send a signal to the rest, you can use the center to cover the Milky Way. You might also look at that center if you want to find a signal.Gajjar and al. Gajjar et al. also suggest that an advanced civilization might be able to tap into the energy from the Milky Way’s central supermassive dark hole to power a galaxie-wide signal beacon. This is a powerful way to say "hello!"The Mojave Desert captures a view towards the galaxy's centre from Earth. (Matthew Cimone).Then, why so quiet?However, none of these answers answer the question "Where are they?" We have not heard anything from anyone because of the speed at which the galaxy could colonize.Caroll-Nellenback and colleagues. Caroll-Nellenback et al. also noted that colonization might have been accelerated by the development of new propulsion technologies, which could reduce spread time. However, radio scans of the galactic center have not yet revealed any signals.Maybe the silence is the answer. Because the galaxy is so vast and there is so much time for life to spread, some people believe that silence will endanger any chance of ever meeting anyone.There is still hope.Simulation shows that it is possible for some parts of the galaxy to never be settled, despite having existed for eons. It is a matter efficiency. You want to colonize within the shortest ranges.Some colonies become extinct over time, possibly due to resource exhaustion or a cataclysmic incident. Instead of reaching further into space, colonies decide to rehabilitate a dying colony closer to home.There are uninhabited planets which never get colonized, and clusters of inhabited colonies. The Milky Way's uninhabited worlds that are too inefficient to colonize can be considered a "steady state".Other explanations for the silence could exist. Long-lived civilizations may be governed by sustainability, which means they grow slower than expected. Multiple colonizing civilizations may be competing for resources, or keeping a distance.Perhaps civilizations are careful not to interfere with inhabited worlds like ours (similarly to Star Trek's Prime Directive) or are aware of possible biological incompatibilities on other worlds. These possibilities could explain why we have not met anyone, unless we are already able to.The Buried PastCarroll-Nellenback and al. Carroll-Nellenback et al. Consider, for instance, that a galactic alien civilization has landed on Earth billions years ago and lived thousands of years before dying off.It would be difficult to find any evidence of their existence after all these years. Although "we" have not met an alien civilization yet, it is possible that Earth has.Simulation shows that, given our galaxy's location, it is probable that at most a million years will pass without interstellar visits. This could be enough time to erase any signs of colonization.It is important to note that the simulation shows that the galaxy can either be completely colonized or completely empty. However, there are middle ground valid responses that still allow for technological extraterrestrial existence even without contact.Globular Life?The galaxy's center is a great place to study SETI, but there are other areas of the galaxy that offer similar conditions.Globular clusters are massive, ancient collections of stars that orbit around the center of the galaxy from distances of tens to thousands of light-years. There are approximately 150 GCs within the Milky Way, which date back to a time of intense star formation that was catalyzed through galaxy mergers. They range in age from 10-13 Billion years.The GCs are extremely dense, with stars that are closer together than in the Milky Way disk. Interstellar communication and travel are often referred to in millennia.A civilization located within a GC, however, would have a travel time between stars of the order of a few years and communication times of months to even weeks. The problem is that GCs can negatively impact the formation of planets and their orbital stability.A. Ray and R. Di Stefano calculate what they call a GC habitable zone. The term "habitable" is used to describe how far a planet must orbit a star in order to sustain temperatures for liquid water. The habitable zone of our Sun is where Earth is located (a good thing). A GC habitable area is not a radius of 2 dimensional like an orbit of a planet. It's a 3 dimensional shell orbiting about the center of the cluster.The shell's inner layer is thinner than the GC density. This is the point where solar systems are able to withstand the gravitational interference from nearby stars. A nearby star's gravity might cause planetary dust rings to break apart, thereby preventing the creation of new planets. A star that passes near a system might also be able to eject a satellite from its parent star.The outer edge of a shell's thickness is determined by the point at which the density is so low that the average distance between stars exceeds 10,000 AU. Astrological units are used to represent Earth's distance from Sun at approximately 150,000 km. 10,000 AU equals approximately 2 light months.The benefits of being in the cluster, namely the quick travel time and easy communication with neighboring stars, diminish after this point. Ray and Di Stefano call this the GC "sweet zone" for colonization star system. It is close enough to facilitate quick travel/communication, but not too close to cause them to break apart.We want the GC sweetspot to include mainly low mass stars that live longer. It is not by chance that low mass stars have the smallest radius of solar habitable zones. The less likely a planet is to be sucked away by another star, the closer it orbits its parent star.Globular cluster, M13. (Howard Trottier/SFU Trottier Observatory).Mass segregation is another phenomenon that GCs experience. This occurs when the largest stars, and therefore those least likely to be habitable in the cluster, gravitationally draw toward the center. This segregation naturally sorts the cluster, from core to periphery, from the least to most desirable choice systems.These results are positive. The sweet spot for a hypothetical GC with 100,000 solar masses is 40 percent of G stars (yellow-darks similar to our Sun) and 15% of K and M stars (orange or red dwarfs) within the cluster. This is a lot of stars.Even if the civilization is capable of capturing solar energy, it is possible that planets that have been ejected out of systems could still be home to a civilization. A space alien free-floating world.Ray and Di Stefano suggest that, even though only 10% of GC stars contain habitable planets and 11% support intelligent life, 11% of those host a communication civilization. This means that at most one civilization could exist in every GC of the Milky Way.Similar variables would be assigned to the Milky Way with a lower stellar density. This would lead to one communicating civilization (probably us). The percentages could be adjusted to be less conservative, so more civilizations would exist in the diffuse disc. However, they would be separated by huge distances exceeding 300 light years.You might try to contact the distant Milky Way disk if you are located in a GC. Unfortunately, we have not been able to locate any evidence that planets exist in GCs. The distance from and densities of the GCs has hampered our ability to find exoplanets. However, it doesn't mean that the possibility isn't possible. Ray and Di Stefano believe that if a civilization exists in a GC with easy access to thousands upon thousands of stars, it would essentially be immortal.We have actually sent a message to a GC about the M13 Hercules globular Cluster. The cluster, which is located in the constellation Hercules is approximately 100,000 stars in diameter and 22,000 lightyears away.1974: M13 received a message from Arecibo's radio telescope (RIP). The message contained the numbers 1-10, chemical compounds of DNA, a graphic figure representing a human and a graphic showing the radio telescope. The broadcast lasted 3 minutes. It still has several thousand years to go.It is likely that the low resolution message will not be detectable by M13. Perhaps we will eventually make contact with another galaxy-spanning civilization. Perhaps WE will be a civilization that spans the galaxy. That story is why I eagerly await the screen adaptation of Asimov’s Foundation series.Universe Today originally published this article. You can read the original article.
