The world nearest to our Earth is a barren, uninhabited Moon. But you can imagine how close to us there would be another inhabited world - perhaps even in the solar system. And how close could he be to us?On our Earth, orbiting around the Sun, we represent the only intelligent life. It is possible that somewhere in the solar system there used to be life, or there are still microbes - but with regard to intelligent, complex, diverse, and multicellular life, our world has overtaken everything we can hope to find here. Intelligent aliens, if they live somewhere in another world, are located at least in light years away from us. But does this necessarily have to be throughout the galaxy? This is what our reader wants to know:
How close can two independent intelligent civilizations exist, without taking into account interstellar travel, and if they developed in different star systems, approximately following the path that we call “life”? In globular clusters, the density of stars can be very large - but does too high density exclude the possibility of habitability of worlds? An astrophysicist living in a dense cluster would have a completely different idea of the Universe and the search for exoplanets.
For the emergence of life, you must go through several stages, but the ingredients for it are
literally everywhere . Even if we confine ourselves to a life that is chemically close to ours, there will be plenty of opportunities in the Universe.
Atoms are able to bind into molecules, including organic ones, both on the planets and in space. Is it possible that life appeared not just before the appearance of the Earth, but also not on the planet at all?For the emergence of rocky planets, organic molecules and the building blocks of life, you need to collect a lot of heavy elements. The universe was not born with them! After the Big Bang, the 99.999999% Universe consisted of hydrogen and helium, and there was no carbon in it. Oxygen, nitrogen, phosphorus, calcium, iron and any other complex elements necessary for life. To reach this stage, it is necessary that several generations of stars live, burn all their fuel, die in a supernova explosion, and re-use the newly formed heavy elements to create the next generation of stars. Neutron star mergers are needed, in which the heaviest elements are born, many of which are in abundance required for life processes on Earth and in our bodies. All this requires a lot of astrophysics.
The Omega Nebula or Messier 17 is an intense, active region of star formation visible to us from the edge — which explains its dusty and ray-shaped appearance. The stars that have been formed at different stages of the Universe development have different proportions of heavy elements.Although the Earth was formed more than 9 billion years ago after the Big Bang, the universe did not have to wait that long. We divide stars into
three types of population :
- Population I: stars like the Sun, in which 1-2% of their constituent elements are heavier than hydrogen and helium. They consist of already recycled material, and in their planetary systems there are gas giants and rocky planets suitable for life.
- Population II: usually older and older stars. The percentage of heavy elements in them is only 0.001-0.1% of what is in the sun, and most of their worlds are rarefied gas. They are too primitive and there are too few heavy elements in them for the appearance of life.
- Population III: the first stars of the universe must be completely unpolluted with heavy elements. They have not yet discovered, but theoretically, these are the first stars.
When studying the earliest galaxies, it can be seen that they are almost entirely composed of stellar population II. But closer to us there is a mixture of young and old, rich and
metal- poor stars.
The distances between the Sun and many nearby stars are shown correctly, but if the drawing were to scale, even the largest of the stars would have been smaller in size than one millionth of a pixel.One of the most important lessons was learned through the Kepler mission when considering the Kepler-444 system. This is the star of population I (with the planets), but they are much, much older than the Earth. Our world is only 4.5 billion years old, and the Kepler-444 system is 11.2 billion years old — that is, the Universe could form worlds similar to the Earth very early — at least 7 billion years earlier than Earth appeared. Given this opportunity, and the fact that areas such as the center of our galaxy have been enriched with metals faster and stronger than ours, it is possible that there are places in the Universe (and perhaps even the Milky Way) that are even more favorable for the emergence of intelligent life, than the Sun-Earth system.
The sugar molecules contained in the gas surrounding the young sun-like star. The basic ingredients of life can exist everywhere, but not every planet containing them can produce life.Given all that we know about the location of the stars, well suited for the origin of life - how close two alien civilizations can be from each other? Where could they be found? How would the answer change depending on the conditions? Let's take a look at five key features.
Fantasy artist on the theme of the system TRAPPIST-1 and its planets, reflected from the surface. The potential of having water on each of the worlds is transmitted through frost, puddles and steam. However, it is unknown whether there is an atmosphere on any of these worlds, or whether their parent star blew them away. One thing is clear - the potentially inhabited worlds are located close to each other, at a distance of only ≈ 1 million km.1) In one solar system. This is just a dream. In the early days of the solar system, it is likely that Venus, Earth, and Mars (and probably even
Teye , a hypothetical planet that collided with the Earth and gave rise to the Moon) were equally suitable for life. Their bark and atmosphere were filled with the ingredients of life, and on the surface was liquid water. Venus and Mars at a distance closest to Earth pass from it in several tens of millions of km: 38 million for Venus and 54 million for Mars. But around the
stars of class M (red dwarfs) the distances between planets are much smaller: in the
TRAPPIST-1 system, there are only about 1 million km between potentially inhabited worlds. Twin moons in orbit around a giant world or a double planet may be even closer to each other. If life began successfully under certain conditions, why did it not originate twice, almost in the same place?
Terrazan 5 globular cluster - view through a very large telescope. Closer to the center of the cluster density is higher, and stability is comparable with any other area.2) In the globular cluster. Globular clusters are massive collections of hundreds of thousands of stars, having the form of spheres with a diameter of several tens of light years. At the outer edges, the typical distance between stars is of the order of a light year, and in the inner parts of the densest clusters, stars can divide relatively short distances, such as the Sun and the
Kuiper belt . The orbits of the planets in these star systems must be stable even in such dense environments, and given what we know about globular clusters that appeared much earlier than Kepler-444, or 11.2 billion years old, there should be good candidates for life and habitability. The distances of several hundred astronomical units, although changing over time due to the movement of the stars, can be called a surprisingly close encounter between the two civilizations.
High resolution photographs in the near infrared range allowed us to discover three star superclusters in the Galactic center . Because light at wavelengths close to infrared penetrates the dense dust located between the Earth and the Galactic center, we were able to see these superclusters. These are the clusters Central Parsek, Kvintiplet and Arches . But all the stars in these clusters, and generally in the Galactic center, are quite young.3) Near the center of the galaxy. The closer you are to the center of the galaxy, the denser the stars are. In several light years from the center, the density of stars is extremely high, much more than in the center of the globular cluster. In a sense, the center of the galaxy is an even denser environment, with large black holes, extremely massive stars and new clusters where stars are forming - none of this is found in globular clusters. But the problem with the stars that we see in the core of the Milky Way is that they are all relatively young. Perhaps due to the high variability of the local environment, stars rarely live there even to a billion years. Despite the high density, these stars are unlikely to have developed civilizations. They just don't live long enough.
Stars are obtained in various sizes, colors and masses, including many bright blue stars, tens or even hundreds of times more massive than the Sun. This is evident in the open cluster of stars NGC 3766 in the constellation Centaurus .4) In a dense star cluster or spiral arm. Okay, so what about star clusters forming in the galactic plane? The spiral arms are denser than normal regions of the galaxy, and it is there that young stars are more likely to appear. The star clusters left from these epochs often contain thousands of stars located on a site just a few light-years in size. But the stars do not stay in this configuration for very long. A typical open star cluster dispersed in just a few million years, and only a small fraction of them live to billions of years. Stars constantly fall in and out of spiral arms, including the sun. In general, even though typical distances between stars inside a cluster can be from 0.1 to 1 light year, they are unlikely to be suitable candidates for the role of the cradles of life.
Logarithmic distance map showing the Voyager spacecraft, our solar system and the nearest star5) Distributed in interstellar space. In other cases, the stars are in a situation that we observe with you: the distances between them are of the order of several light years. Approaching the center of the galaxy, this distance can be reduced to those found in open clusters - from 0.1 to 1 light year. But if you get too close, we will face the problem that we see in the center of the galaxy: mergers, interactions, other catastrophes, most likely interfering with your stable environment. You can reduce the distance, but a typical interstellar space will not do. If you insist on convergence, then the best option would be to wait until another star passes close to the original one - and with a typical star this happens once in about one million years.
Graph of the probability of passage of a star at a certain distance from the sun. The logarithmic graph in both axes.And although we do not expect that intelligent alien life will turn out to be a frequent phenomenon in the Universe, as frequent as planets and stars — every world satisfying the necessary conditions is a chance. And every time you get a chance, you get a chance of success with a finite probability. Each of these features may be a reality! The probability of such an event may be low, but until we go there and see what is there and what is not there, it is vital to objectively evaluate what alien mind the Universe can provide us. The truth is definitely somewhere there, but it is important to understand that if we were very lucky, it could be much closer than we even dare to imagine today!