Friday, November 24, 2017

Rich Clouds, Poor Clouds

It seems that normal stars do not produce the amounts of heavier elements, those higher in atomic number than iron, that are observed in the galaxy. Some other source is indicated. One theory involves a collision between two neutron stars. This might be effected by starting with a binary with two neutron stars. In a binary with only one neutron star, it eats up the atmosphere of the other star. But a neutron star has no atmosphere similar to a normal sequence star, so one cannot strip mass from another. They have little to do but radiate energy and eventually collide, leading to another type of explosion.

This makes sense, as higher elements are formed by neutrons being added to lower elements’ nuclei, and a neutron star is nothing but neutrons. An explosion would lead to the rapid formation of elements, but the spectrum would be quite different from that of a stellar interior, where elements are kept in equilibrium by a very different set of processes.

One question this theory raises is how well a binary can survive a supernova explosion of one of the two stars involved. Perhaps a well-separated binary could survive it, with only a orbital change, perhaps from near circular to an orbit with large eccentricity. Would the first supernova strip off part of the atmosphere of its binary companion, reducing the amount of fuel for it to burn, and thereby hastening the second supernova? This theory of binary neutron stars raises many intriguing questions.

Binary stars do form fairly frequently, so it would make sense that some of them would have two stars which could both evolve into neutron stars. It’s not exactly clear what would happen if one of the stars became a black hole, just barely. Perhaps the same type of collision would also add to the heavier elements.

A fairly obvious question arising from this is: Are clouds uniform in the production of double neutron star binaries? Are clouds which are larger or smaller, more or less dense, more or less turbulent,more or less spherical, hotter or colder, dustier or more gaseous, more likely to produce these special binaries? There are many parameters by which clouds can be described, and it would seem some of these would affect the production of predecessor stars to neutron stars, and binaries to boot. If these factors do play a role in the relative density of these binaries, then around the galaxy there would be, sometime into the lifetime of the galaxy, clouds which are rich in heavier elements and clouds which are poor in heavier elements.

If the technology development of an intelligent species requires the presence, on the planet, of a certain amount of heavier elements, this means that some clouds in the Milky Way are more prone to civilizations which can eventually travel to other stars, and other clouds are too deficient to allow any intelligent species to climb high enough in technology to do this.

Clouds are much larger than solar systems or intersolar distances, so this means the galaxy might be like a large continent, part of which was habitable with rain and rivers and vegetation, while other large areas were barren deserts. Similarly, it would mean that travel within one’s original cloud might be much easier than from one heavy-element-rich cloud to another. Huge distances would have to be traveled, in comparison to the typical interstellar ones. Just to provide some food for thought, suppose the distance between good planets was 100 light years in a rich cloud, and the distance to another rich cloud might be 10,000 light years. While it might be reasonable to travel the first, the second might be simply too far. Thus, the galaxy would be necessarily divided into pieces which cannot communicate between one another.

The heavier element distribution is an additional galactic distribution factor on top of the diversity that already is known to exist, with different major components such as the bulge and the disk, and the variations known to exist in the disk with the rotating spiral density waves and the gulfs between them. Cloud density variations are huge to begin with, and with this latest theory on the peculiar ways in which heavier elements are formed, there is yet another factor contributing to the geography of the galaxy.

It should be possible for an advanced alien civilization to map out the distribution of heavier elements in the galaxy, using large wide spectrum photon collectors. They would therefore know, before they made any decision as to seeding other planets or doing anything else interstellar, just how much territory they could operate in. They might find out that they are in an extreme situation themselves.

If the density distribution of heavier elements is very peaked, in other words, the processes that make heavier elements, such as the proposed neutron star collisions, are quite rare, and there are only a few pockets within the galaxy where there are higher densities of these elements, then they might find that there is no hope to seed the galaxy. Basically they might find they were in one pocket, that there were no other similar solar systems within that pocket, and the nearest other pocket was on the opposite side of the galaxy, much too far to travel to under any circumstances at all.

This distribution may be yet another surprise awaiting Earth scientists as they explore the galaxy. Right now in our history we are just beginning to understand the galactic environment that we live in, and the question that has caught our fancy is the possibility of life originating on other planets. For this we search for some attributes which might be signatures of life. But it could very well turn out in a few years or decades that we realize that we are indeed located in a very unique corner of the galaxy and are the only ones alive and civilized at this time. The galaxy is too harsh a place for life to evolve and develop a technological civilization except in only a tiny fraction of the existing solar systems.

Another implication of this is that heavier elements might take billions of years to accumulate, so that if we had come into existence five billion years later, the galaxy might have many more alien civilizations, traveling from one star system to another or at least communicating between one another. It is too bad we can’t wait around for all the excitement to begin.

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